IIgs Monitor Repair
Polymorph
I have a couple of questions relating to repairing a monitor for my
daughters IIgs.
For well over a year now, I have had an old Amiga monitor hooked up to
the IIgs via a SCART adapter (courtesy of VintageWare). Unfortunately,
2 days before Christmas something in the monitor died. It was working
fine, then all of a sudden the picture went out and it started making
a loud whirring/whining sound (almost like something rotating). I
thought it might have been the electrolytic capacitors in the power
supply, so I replaced them all; but the situation did not improve.
However, I now believe the noise to possibly be coming from the "fly-
back" transformer. Does this sound likely? If it is, is it worth
repairing as I could not find any details regarding the make/model of
this transformer. Also, I could not find a schematic for the monitor.
I am thinking this might now be a dead-issue, but wanted some experts
opinions before giving up on it.
Also, I have a standard AppleColor RGB (IIgs) monitor that I have now
replaced the above dead Amiga monitor with, however it has issues of
its own (which is why I was using the Amiga monitor in the 1st place).
This monitor starts off clear and sharp but with low contrast/
brightness; so you need to have both turned up high to get a good
picture. The picture gradually gets brighter and brighter and the
image quality deteriorates and loses focus (gets very blurry and hard
to read). After about 30 minutes, the contrast brightness is very high
and the image is very blurry (almost to the point of hurting your
eyes).
Now this problem sounds very much like the problem mentioned in Q.34
of the Apple II Monitors FAQ which I will now quote the question and
answer:
"034- I picked up a IIgs RGB monitor at a garage sale. The focus is
off and it took several minutes until the display got brighter
but it's still not very good. Are there any adjustments that can
be made?
The problem you describe is consistant with low B+ going to the
flyback
transformer which results in low brightness level, poor focus, and
blooming
when the brightness and/or screen level is turned up. More than likely
if this
monitor has been sitting around for awhile, the filter capacitors have
gone to
mush. Sometimes they can be revived by leaving the monitor on for a
long period
of time <over 24hrs> but, usually, they require replacement. "
Now, as this sounds *very* similar to the problem I'm seeing, I'd like
to try and replace the main filter capacitors as described in the
answer. The question I have though is - which are the "filter
capacitors" in the monitor? I cracked the case open the other day, and
there is one big 450V cap near the power supply. Is this the one being
referred to, or is it somewhere else?
Any help would be much appreciated as I'd like to get my daughters
IIgs running perfectly again. Either that or I'll be on the lookout
for a replacement monitor.
thanks,
Mike
Michael J. Mahon
> Hi All,
>
> I have a couple of questions relating to repairing a monitor for my
> daughters IIgs.
>
> For well over a year now, I have had an old Amiga monitor hooked up to
> the IIgs via a SCART adapter (courtesy of VintageWare). Unfortunately,
> 2 days before Christmas something in the monitor died. It was working
> fine, then all of a sudden the picture went out and it started making
> a loud whirring/whining sound (almost like something rotating). I
> thought it might have been the electrolytic capacitors in the power
> supply, so I replaced them all; but the situation did not improve.
> However, I now believe the noise to possibly be coming from the "fly-
> back" transformer. Does this sound likely?
Very likely.
> If it is, is it worth
> repairing as I could not find any details regarding the make/model of
> this transformer. Also, I could not find a schematic for the monitor.
> I am thinking this might now be a dead-issue, but wanted some experts
> opinions before giving up on it.
Audio frequency sounds coming from a flyback transformer can easily
result from "squegging" of the horizontal oscillator and/or horizontal
output stage.
These circuits can be difficult to diagnose because of the various
feedback loops involved--like switching power supplies. A schematic
is very useful.
It is probably worth replacing the electrolytic capacitors in the
horizontal output stage, since a radically changed value or an
open or leaking capacitor can cause symptoms similar to what you
describe.
Odds are good that the hard-to-replace flyback transformer and
horizontal output transistor are still OK, and that replacing
capacitors (or any other dubious passive components) will fix
the monitor.
That certainly is one. Any relatively high voltage electrolytics are
likely "filter capacitors" and are also among the lowest reliability
components in a monitor.
Sometimes a non-electrolytic capacitor used as a coupling capacitor
will get "leaky" (meaning that it begins to have a DC resistance
considerably less than infinite ;-), causing slow drift in DC bias--
for example, in the CRT grid, cathode, or focus electrode circuits--
which will also lead to a shift in brightness and focus.
> Any help would be much appreciated as I'd like to get my daughters
> IIgs running perfectly again. Either that or I'll be on the lookout
> for a replacement monitor.
I suspect that in the years ahead, we will have to get good at
repairing these monitors...
-michael
NadaPong: Network game demo for Apple II computers!
Home page: http://members.aol.com/MJMahon/
"The wastebasket is our most important design
tool--and it's seriously underused."
Polymorph
Thanks Michael, your experience with such matters always proves very
handy when these obstacles present themselves. :-)
I'll crack open the AppleColor RGB monitor tomorrow, take an inventory
of the electrolytic capacitors it has; and head to the local
electronics dealer (Jaycar). Hopefully with a few replaced capacitors,
the monitor will look nice and sharp permanently. I will take
photographs during the procedure, and if it solves my problem then I
will post details/photos online to help out others who may experience
this same problem (as it is mentioned in the FAQ I expect it has
happened more than a few times before). If it doesn't work, I'll be
too busy bashing my head against the wall to post anything. ;-)
Its just a shame that the capacitors that I installed into the
recently deceased Amiga monitor were of different voltages and
capacitances, otherwise I could have re-used them.
Also, upon inspection of the old Amiga monitor circuit board, I
noticed something that looks kinda weird and maybe possible damage. It
looks like an inductor, has come away from 2 of its support posts. See
the following images:
http://www.cirruscomms.com.au/~mike_stephens/Inductor01.jpg
http://www.cirruscomms.com.au/~mike_stephens/Inductor02.jpg
I don't know whether this is normal, but it sure looked suspicious,
especially since it is very close to the flyback transformer. Could
this be a possible cause for the problems I'm having? I may try
desoldering it and taking a closer look. I know very little about
inductors, but it didn't look "normal" to me. I could be barking up
the wrong tree here though.
Thanks,
Mike
fer...@gmx.de
> Its just a shame that the capacitors that I installed into the
> recently deceased Amiga monitor were of different voltages and
> capacitances, otherwise I could have re-used them.
>
> Also, upon inspection of the old Amiga monitor circuit board, I
> noticed something that looks kinda weird and maybe possible damage. It
> looks like an inductor, has come away from 2 of its support posts. See
> the following images:
>
>
> I don't know whether this is normal, but it sure looked suspicious,
> especially since it is very close to the flyback transformer. Could
> this be a possible cause for the problems I'm having? I may try
> desoldering it and taking a closer look. I know very little about
> inductors, but it didn't look "normal" to me. I could be barking up
> the wrong tree here though.
>
This is NOT normal at all. But according to the silkscreen on the
board the two pins which are pulled out don't seem to be connected.
you can check this from the bottom of the board.
If the other two pins are ok, the coil might still be fine. A good
coil will always measure a very low resistance. For this coil I'd
expect <5Ω.
With a horizontal deflection problem I first check the Horizontal
Output Transistor for shorts. The Collector (middle pin) should not be
shorted to either Emitter or Base. If it is, there are 4
possibilities:
1) Blown HOT. Note that this may be caused by a blown flyback, snubber
cap or damper diode. If you can't obtain an exact replacement, a
BU2725D should do. It also has an integrated damper diode so it won't
blow if the damper is blown.
2) Blown damper diode. It is connected over the HOT from collector to
emitter (there may be some small resistors/indutors though). Note that
it may be integrated into the HOT. A datasheet will tell.
3) Blown power supply recitifier. This only applies when a switching
power supply is used (which I expect in a monitor).
4) Blown B+ filter caps. These will be rated at >22µF/100V. I'd expect
47µF/200V.
Always unsolder them and check for shorts.
If there is no short, then check for voltage on the HOT collector (use
an analog meter if possible, use the 1000V scale, if available and
fix the probes. Do not tap into there!) The voltage should be between
60 and 200V. If there is not, this is either a flyback or a power
supply problem (may be just a blown fuse or resistor. If you'd make a
photo of the whole horizontal section I could tell you which are
suspect).
If there is voltage, it get difficult. #
The first thing I would do is to resolder all big solder joints (and
all that look suspect). This might be a good idea anyway.
If the HOT was blown, you should check if the damper diode is ok
(measure resistance in both directions with the diode unsoldered-
should be infinite in one and something like 1000 Ω in the other
direction.)
Checking the snubber cap is difficult. It is connected from HOT
collector to ground somewhere. If there's a pincushion adjustment it
might be split into two caps in series. There will also be two damper
diodes then. If in doubt, just replace it a blown snubber will cause
the HOT to blow instantly and testing small caps is a really tough
job.
For mor information, read the RepairFAQ:
http://www.repairfaq.org/sam/monfaq.htm
Ferdinand Meyer-Hermann
heuser...@freenet.de
>
> Also, upon inspection of the old Amiga monitor circuit board, I
> noticed something that looks kinda weird and maybe possible damage. It
> looks like an inductor, has come away from 2 of its support posts. See
> the following images:
>
> http://www.cirruscomms.com.au/~mike_stephens/Inductor01.jpg
> http://www.cirruscomms.com.au/~mike_stephens/Inductor02.jpg
>
> I don't know whether this is normal, but it sure looked suspicious,
> especially since it is very close to the flyback transformer. Could
> this be a possible cause for the problems I'm having? I may try
> desoldering it and taking a closer look. I know very little about
> inductors, but it didn't look "normal" to me. I could be barking up
> the wrong tree here though.
They look like indivual testing points of some kind.
What model is the monitor? I may have a schematic.
bye
Marcus
Polymorph
The monitor is a Philips CM17029/75G. Any info about this monitor
would be great.
Thanks,
Mike
Michael J. Mahon
If I've encouraged you to try repairing it, I'm glad!
> I'll crack open the AppleColor RGB monitor tomorrow, take an inventory
> of the electrolytic capacitors it has; and head to the local
> electronics dealer (Jaycar). Hopefully with a few replaced capacitors,
> the monitor will look nice and sharp permanently. I will take
> photographs during the procedure, and if it solves my problem then I
> will post details/photos online to help out others who may experience
> this same problem (as it is mentioned in the FAQ I expect it has
> happened more than a few times before). If it doesn't work, I'll be
> too busy bashing my head against the wall to post anything. ;-)
;-)
> Its just a shame that the capacitors that I installed into the
> recently deceased Amiga monitor were of different voltages and
> capacitances, otherwise I could have re-used them.
If the physical size is compatible, capacitors with higher
voltage ratings are no problem, and often electrolytics with
up to twice the capacitance are OK too. (Electrolytic caps
have pretty wide tolerances on capacitance, so exact values
are usually irrelevant as long as the minimum requirement is met.)
> Also, upon inspection of the old Amiga monitor circuit board, I
> noticed something that looks kinda weird and maybe possible damage. It
> looks like an inductor, has come away from 2 of its support posts. See
> the following images:
>
> http://www.cirruscomms.com.au/~mike_stephens/Inductor01.jpg
> http://www.cirruscomms.com.au/~mike_stephens/Inductor02.jpg
>
> I don't know whether this is normal, but it sure looked suspicious,
> especially since it is very close to the flyback transformer. Could
> this be a possible cause for the problems I'm having? I may try
> desoldering it and taking a closer look. I know very little about
> inductors, but it didn't look "normal" to me. I could be barking up
> the wrong tree here though.
It may have four "legs" but only two connections--that is, it may
be just a simple inductor, not a transformer or tapped inductor.
In that case, the problem is just mechanical, and a good indication
that either someone was poking around in there or the monitor received
a pretty good physical shock at some time.
If there are wires from the inductor soldered to either of those
two (relatively) disconnected posts, they should be carefully re-
soldered. If not, then just gently re-positioning the inductor
will improve the esthetics (but probably won't change the behavior
of the circuit).
Polymorph
<snip>
> If the physical size is compatible, capacitors with higher
> voltage ratings are no problem, and often electrolytics with
> up to twice the capacitance are OK too. (Electrolytic caps
> have pretty wide tolerances on capacitance, so exact values
> are usually irrelevant as long as the minimum requirement is met.)
OK, I knew you could use a higher voltage capacitor, but I didn't know
you could use one with a higher capacitance. Thanks for the tip! The
problem is, I went to Jaycar today (our local electronics supplier)
and found that they do not stock a 150uF 450V electrolytic cap - the
highest they stock is 100uF 400V, so I didn't bother buying anything
yet until I can source the right caps.
I had another idea anyhow, as I have another IIgs monitor that is
working OK, I thought I might try removing caps from it and use them
in the problematic monitor - trying one at a time until (*hopefully*)
the problem goes away. That way I should be able to isolate the
problem cap and replace only it. It will involve more work, but might
be the best way of debugging the problem? Again, experts thoughts are
welcome - I'm most definitely out of my comfort zone (please remember,
I'm a software guy, cutting his teeth in hardware) and I'm mostly
winging it with educated guesses. :-)
<snip>
> It may have four "legs" but only two connections--that is, it may
> be just a simple inductor, not a transformer or tapped inductor.
>
> In that case, the problem is just mechanical, and a good indication
> that either someone was poking around in there or the monitor received
> a pretty good physical shock at some time.
>
> If there are wires from the inductor soldered to either of those
> two (relatively) disconnected posts, they should be carefully re-
> soldered. If not, then just gently re-positioning the inductor
> will improve the esthetics (but probably won't change the behavior
> of the circuit).
My "research" into inductors hinted that this may be the case because
all examples I came across only had two live connections (as I
mentioned previously, I know virtually nothing about inductors).
Thanks,
Mike
Polymorph
> On Dec 26, 7:23 am, Polymorph <polymorp...@hotmail.com> wrote:
>
>
>
> > Its just a shame that the capacitors that I installed into the
> > recently deceased Amiga monitor were of different voltages and
> > capacitances, otherwise I could have re-used them.
>
> > Also, upon inspection of the old Amiga monitor circuit board, I
> > noticed something that looks kinda weird and maybe possible damage. It
> > looks like an inductor, has come away from 2 of its support posts. See
> > the following images:
>
Ferdinand,
Thanks for the reply, you certainly sound like you know what you're
talking about. Unfortunately for me, I'm still trying to learn my way,
and I didn't understand a lot of what you were talking about. Maybe
when I read the monitor repair FAQ in detail (I did scan over it
briefly) I might have a better understanding of what you were on
about.
I will be initially concentrating on getting the AppleColor monitor
working properly (mostly due to my study being filled up with semi-
deconstructed monitors), then I will return to the old Amiga monitor
once that is done. I'll post as much detail as is needed, because it
was a good monitor and I'm sorry to see it out of action - one thing I
definitely miss is the monitors inbuilt speaker with volume control.
Because I was using a SCART interface, audio information was also
being sent to the monitor and the volume control on the monitor was
*much* easier to use than having to go into the IIgs control panel.
thanks,
Mike
fer...@gmx.de
> I had another idea anyhow, as I have another IIgs monitor that is
> working OK, I thought I might try removing caps from it and use them
> in the problematic monitor - trying one at a time until (*hopefully*)
> the problem goes away. That way I should be able to isolate the
> problem cap and replace only it. It will involve more work, but might
> be the best way of debugging the problem? Again, experts thoughts are
> welcome - I'm most definitely out of my comfort zone (please remember,
> I'm a software guy, cutting his teeth in hardware) and I'm mostly
> winging it with educated guesses. :-)
>
There is a simpler trick: get a tool that allows to heat or cool the
caps. This could be:
- a hair dryer or heat gun
- your soldering iron
- a candle or a lighter/matches if used with care
- cold spray
try to heat/cool any suspect cap and see if the problem changes.
If it does, you found a bad cap.
Ferdinand
Michael J. Mahon
Unfortunately, this only works when the monitor is working well
enough to be able to observe changes. Temperature changes will
hardly ever restore function to a dried-out electrolytic.
It can be quite effective for potentially (electrically) leaky
non-electrolytic capacitors, and for any thermal intermittent.
Bridging electrolytics with a suitable test capacitor is very
effective at isolating failing capacitors.
Michael J. Mahon
> On Dec 27, 8:41 pm, "Michael J. Mahon" <mjma...@aol.com> wrote:
>
> <snip>
>
>>If the physical size is compatible, capacitors with higher
>>voltage ratings are no problem, and often electrolytics with
>>up to twice the capacitance are OK too. (Electrolytic caps
>>have pretty wide tolerances on capacitance, so exact values
>>are usually irrelevant as long as the minimum requirement is met.)
>
>
> OK, I knew you could use a higher voltage capacitor, but I didn't know
> you could use one with a higher capacitance. Thanks for the tip! The
> problem is, I went to Jaycar today (our local electronics supplier)
> and found that they do not stock a 150uF 450V electrolytic cap - the
> highest they stock is 100uF 400V, so I didn't bother buying anything
> yet until I can source the right caps.
You may need to go mail order for a larger selection.
> I had another idea anyhow, as I have another IIgs monitor that is
> working OK, I thought I might try removing caps from it and use them
> in the problematic monitor - trying one at a time until (*hopefully*)
> the problem goes away. That way I should be able to isolate the
> problem cap and replace only it. It will involve more work, but might
> be the best way of debugging the problem? Again, experts thoughts are
> welcome - I'm most definitely out of my comfort zone (please remember,
> I'm a software guy, cutting his teeth in hardware) and I'm mostly
> winging it with educated guesses. :-)
Actually, substitution is a time-honored and excellent method of
isolating a failing component.
A couple of notes:
1. Sometimes a component has failed as a consequence of stress
induced by *another* failure--for example, a resistor may have
"smoked" because of a shorted capacitor. In cases like this,
substitution of a good component can result in damage to the
good component, if the source of the problem is not fixed
earlier.
2. Many components have a predominant failure mode that makes the
substitution much simpler. For example, electrolytics tend to
fail "open" (or low-capacitance), which means that substitution
can be easily tried by "bridging" (connecting in parallel) the
possibly failed capacitor with a known-good capacitor of an
appropriate voltage and capacitance (in this case, from 1/2 to
2x the substituted capacitor).
If the circuit then works better, the bridged capacitor is likely
faulty. (Watch polarity, of course!)
heuser...@freenet.de
>
> The monitor is a Philips CM17029/75G. Any info about
> this monitor would be great.
Philips built the Amiga monitors which sometimes are only
simply renamed. Most of these have very similar features
and probably mostly similar board layouts / components.
I have a schematic of an Amiga 1081 monitor and it may
help but I need the part number that is silk screened on
you board - the photos are not usable.
bye
Marcus
Polymorph
Apologies for the delay in reply (I was on holidays!).
I have spent some time today trying to repair the problematic
AppleColor IIgs monitor. As I mentioned in a previous post, I have
been taking caps from a working monitor to replace the high voltage
caps in the defective monitor one at a time, but I have still not
found the cause of the problem.
The caps I've replaced are:
* 150uF / 450V Schematic reference: C906
* 22uF / 200V Schematic reference: C613
* 330uF / 180V Schematic reference: C951
* 100uF / 100V Schematic reference: C409
I will continue to keep replacing the high voltage caps >= 100V. Is
this a reasonable value to use as "high voltage"?
If the problem is still present after replacing all the high voltage
caps, is it worthwhile continuing replacing the lower voltage
electrolytics, or should I start suspecting something else as the
failure? Michael, you mentioned some non-electrolytic capacitors as
possibly being responsible. How would I find the ones you described?
Bear in mind the schematics for the IIgs monitor are available (I have
downloaded them) from Tony Diaz's info site - http://apple2.info/. So
hopefully you (or someone else) can describe what I should be looking
for, or better yet, point out on the schematic the likely ones. ;-)
Any help would be appreciated.
Thanks,
Mike
Polymorph
Marcus,
Sorry for not getting back sooner, but I've been on holidays and had
no access to a PC. Thanks for the info regarding Amiga monitors being
built by Philips - it was something I suspected, but I wasn't sure.
I currently have two AppleColour IIgs monitors pulled apart in my
study and I don't have the room to re-open the Philips monitor just
yet. Hopefully I'll get the faulty AppleColor monitor working again,
at which time I can start looking at the Philips once more. Once I
have the details that are silk screened onto the board, I'll post them
here - hopefully they'll match one of the schematics that you have.
Thanks again,
Mike
heuser...@freenet.de
>
> Hopefully I'll get the faulty AppleColor monitor working again,
> at which time I can start looking at the Philips once more.
> Once I have the details that are silk screened onto the board,
> I'll post them here - hopefully they'll match one of the
> schematics that you have.
Anytime, Mike.
The schematics don't fade ;-)
bye
Marcus
Michael J. Mahon
Likewise! ;-)
> I have spent some time today trying to repair the problematic
> AppleColor IIgs monitor. As I mentioned in a previous post, I have
> been taking caps from a working monitor to replace the high voltage
> caps in the defective monitor one at a time, but I have still not
> found the cause of the problem.
>
> The caps I've replaced are:
>
> * 150uF / 450V Schematic reference: C906
> * 22uF / 200V Schematic reference: C613
> * 330uF / 180V Schematic reference: C951
> * 100uF / 100V Schematic reference: C409
>
> I will continue to keep replacing the high voltage caps >= 100V. Is
> this a reasonable value to use as "high voltage"?
As I noted earlier, you may find it much easier to simply use one
or two known-good electrolytics to "bridge" across the terminals
of each suspected capacitor until you find the one that makes a
(positive ;-) difference.
A 100uF 450v capacitor is a good "high range" test capacitor, and
a 22uF 450v capacitor would be a good "low range" one.
This saves a lot of unsoldering and soldering and works well in
the vast majority of cases.
I should point out that it is a good idea to discharge the test
capacitor after each "bridging" operation, since residual charge
could disrupt or damage another circuit. Of course, discharging
is good after you're done, too! ;-)
> If the problem is still present after replacing all the high voltage
> caps, is it worthwhile continuing replacing the lower voltage
> electrolytics, or should I start suspecting something else as the
> failure?
Using the bridging technique really lowers the penalty for checking
out most of the other capacitors, and electrolytics are still the
most likely failure candidates.
> Michael, you mentioned some non-electrolytic capacitors as
> possibly being responsible. How would I find the ones you described?
> Bear in mind the schematics for the IIgs monitor are available (I have
> downloaded them) from Tony Diaz's info site - http://apple2.info/. So
> hopefully you (or someone else) can describe what I should be looking
> for, or better yet, point out on the schematic the likely ones. ;-)
I'll take a look and see.
What exactly is the symptom, again?
Polymorph
<snip>
> As I noted earlier, you may find it much easier to simply use one
> or two known-good electrolytics to "bridge" across the terminals
> of each suspected capacitor until you find the one that makes a
> (positive ;-) difference.
>
> A 100uF 450v capacitor is a good "high range" test capacitor, and
> a 22uF 450v capacitor would be a good "low range" one.
>
> This saves a lot of unsoldering and soldering and works well in
> the vast majority of cases.
I do have a 100uF 450V cap, but I do not have a 22uF 450V to attempt
testing in parallel. I do have a 47uF 200V cap; would that be
suitable? By the way, what is the best way to discharge a capacitor?
(Told you I'm still learning :-) ).
I must admit, apart from the two largest caps (one of which required
the removal of metal shielding), the other caps have been relatively
simple to desolder, so I'm happy enough to keep going that way for
now.
>
> > If the problem is still present after replacing all the high voltage
> > caps, is it worthwhile continuing replacing the lower voltage
> > electrolytics, or should I start suspecting something else as the
> > failure?
>
> Using the bridging technique really lowers the penalty for checking
> out most of the other capacitors, and electrolytics are still the
> most likely failure candidates.
>
> > Michael, you mentioned some non-electrolytic capacitors as
> > possibly being responsible. How would I find the ones you described?
> > Bear in mind the schematics for the IIgs monitor are available (I have
> > downloaded them) from Tony Diaz's info site -http://apple2.info/. So
> > hopefully you (or someone else) can describe what I should be looking
> > for, or better yet, point out on the schematic the likely ones. ;-)
>
> I'll take a look and see.
>
> What exactly is the symptom, again?
The symtoms are as follows: when the monitor is first switched on, the
contrast / brightness is quite low but the picture is nice and sharp.
By turning the up brightness / contrast a little, you get quite a good
image. However, after about 10 minutes the monitors picture starts
getting noticeably brighter and continues to do so. After about 30
minutes, the image has become really bright and the focus has degraded
to a point that hurts your eyes. Lowering the brightness / contrast
doesn't help as the image is all blurry and very hard on the eyes. If
you look back through the history of this thread, I posted one of the
Apple II FAQ questions and answers which sounds remarkably like what
I'm seeing - this is what started me replacing "filter" capacitors.
Thanks for your help.
Cheers,
Mike
Michael J. Mahon
> On Jan 6, 11:48 am, "Michael J. Mahon" <mjma...@aol.com> wrote:
>
> <snip>
>
>>As I noted earlier, you may find it much easier to simply use one
>>or two known-good electrolytics to "bridge" across the terminals
>>of each suspected capacitor until you find the one that makes a
>>(positive ;-) difference.
>>
>>A 100uF 450v capacitor is a good "high range" test capacitor, and
>>a 22uF 450v capacitor would be a good "low range" one.
>>
>>This saves a lot of unsoldering and soldering and works well in
>>the vast majority of cases.
>
>
> I do have a 100uF 450V cap, but I do not have a 22uF 450V to attempt
> testing in parallel. I do have a 47uF 200V cap; would that be
> suitable? By the way, what is the best way to discharge a capacitor?
> (Told you I'm still learning :-) ).
The 47uF cap is fine for bridging capacitors rated up to 200v.
For typical (not super-low ESR) electrolytics, the easiest way
is to short the terminals for at least a second.
Don't use a metal tool you care about for a 100uF 450v cap that
is charged over 300v, since the spark is quite energetic. ;-)
Just from the description (haven't checked the schematic yet), it sounds
like it could be an unstable high voltage resistor or capacitor in the
CRT focus anode circuit.
I'll check the schematic... ;-)
fer...@gmx.de
> On Jan 6, 11:48 am, "Michael J. Mahon" <mjma...@aol.com> wrote:
>
> <snip>
>
> > As I noted earlier, you may find it much easier to simply use one
> > or two known-good electrolytics to "bridge" across the terminals
> > of each suspected capacitor until you find the one that makes a
> > (positive ;-) difference.
>
> > A 100uF 450v capacitor is a good "high range" test capacitor, and
> > a 22uF 450v capacitor would be a good "low range" one.
>
> > This saves a lot of unsoldering and soldering and works well in
> > the vast majority of cases.
>
> I do have a 100uF 450V cap, but I do not have a 22uF 450V to attempt
> testing in parallel. I do have a 47uF 200V cap; would that be
> suitable? By the way, what is the best way to discharge a capacitor?
> (Told you I'm still learning :-) ).
>
connect a ~5kΩ across it. Don't use a small 1/4Watt resistor, you will
just set it on fire! I use 5W ceramic resistors, but a 1W resistor is
ok too. Don't hold it with you fingers, because there may voltages you
don't want touch.
Screwdriver discharge is NOT a good idea at all. It can damage the cap
and it can blow other devices (I used a screwdriver some time ago and
blew a TV set's control logic beyond repair).
> I must admit, apart from the two largest caps (one of which required
> the removal of metal shielding), the other caps have been relatively
> simple to desolder, so I'm happy enough to keep going that way for
> now.
>
>
(electrically speaking...)
> > > If the problem is still present after replacing all the high voltage
> > > caps, is it worthwhile continuing replacing the lower voltage
> > > electrolytics, or should I start suspecting something else as the
> > > failure?
>
> > Using the bridging technique really lowers the penalty for checking
> > out most of the other capacitors, and electrolytics are still the
> > most likely failure candidates.
>
But you'll have for a warm-up every time.
> > > Michael, you mentioned some non-electrolytic capacitors as
> > > possibly being responsible. How would I find the ones you described?
> > > Bear in mind the schematics for the IIgs monitor are available (I have
> > > downloaded them) from Tony Diaz's info site -http://apple2.info/. So
> > > hopefully you (or someone else) can describe what I should be looking
> > > for, or better yet, point out on the schematic the likely ones. ;-)
>
> > I'll take a look and see.
>
> > What exactly is the symptom, again?
>
> The symtoms are as follows: when the monitor is first switched on, the
> contrast / brightness is quite low but the picture is nice and sharp.
> By turning the up brightness / contrast a little, you get quite a good
> image. However, after about 10 minutes the monitors picture starts
> getting noticeably brighter and continues to do so. After about 30
> minutes, the image has become really bright and the focus has degraded
> to a point that hurts your eyes. Lowering the brightness / contrast
> doesn't help as the image is all blurry and very hard on the eyes. If
> you look back through the history of this thread, I posted one of the
> Apple II FAQ questions and answers which sounds remarkably like what
> I'm seeing - this is what started me replacing "filter" capacitors.
>
I don't really believe this is a filter capacitor problem.
It sounds more like a problem in the HV divider section. This can be
verified with a simple test. You should see the fat wire coming from
the top of the picture tube. This wire leads to the Flyback
transformer, which also has the HV divider in it (the part with the
two or three trim pots). The lowest pot (usually labeled SCREEN) is
sort of a master brightness control. With it, the brightness can be
varied from a completely black screen to an extremely bright white
screen. The other controls are focus controls.
Fire up the monitor with a picture and first find out what the pots do
by turning them until something happens. If you know how they work,
leave the monitor on and try to correct the picture while the monitor
warms up. If it is possible to get a good picture or if they don't
have enough range to correct (might happen to the focus, unlikely with
screen) then the divider is propably bad.
Another idea would be to measure the voltage on the G2 terminals on
the CRT socket. It shouldn't change at all. But note that there might
be no picture as long as the meter is connected.
If the picture can't be improved using these controls you might either
have
a) a fault in the G1 supply (test voltage on G1. It shouldn't change
from cold to warm)
b) a fault in the video amplifier or supply (measure voltage on the
CRT cathodes (usually labeled R,G,B). This should not change as long
as the Picture is the same.)
Because all three colors are affected I'd expect a supply problem.
BTW: Many monitors have voltages printed next to some points
(especially connectors). Check these!
If you know where to look for the fault then you can trace the wires
and replace the caps you find on the way.
If the divider is bad, you're in trouble. These are not easily
obtainable and very expensive. The only sensible repair would be to
get another flyback transformer and transplant the HV divider.
This procedure is decribed in the Repairfaq as "Focus/Screen divider
bypass surgery".
---
Ferdinand Meyer-Hermann
Polymorph
<snip excellent advice>
Thanks Ferdinand!
I will try your suggestions and see if I can either fix the problem,
or at least figure out what might be wrong.
Cheers,
Mike
Michael J. Mahon
--
Michael J. Mahon
fer...@gmx.de wrote:
> On 6 Jan., 02:42, Polymorph <polymorp...@hotmail.com> wrote:
>
>>On Jan 6, 11:48 am, "Michael J. Mahon" <mjma...@aol.com> wrote:
>>
>><snip>
>>
>>>As I noted earlier, you may find it much easier to simply use one
>>>or two known-good electrolytics to "bridge" across the terminals
>>>of each suspected capacitor until you find the one that makes a
>>>(positive ;-) difference.
>>
>>>A 100uF 450v capacitor is a good "high range" test capacitor, and
>>>a 22uF 450v capacitor would be a good "low range" one.
>>
>>>This saves a lot of unsoldering and soldering and works well in
>>>the vast majority of cases.
>>
>>I do have a 100uF 450V cap, but I do not have a 22uF 450V to attempt
>>testing in parallel. I do have a 47uF 200V cap; would that be
>>suitable? By the way, what is the best way to discharge a capacitor?
>>(Told you I'm still learning :-) ).
>>
>
> a 47µF cap should be ok.
But his 47uF 200v cap should not be used to bridge any capacitor
rated over 200v!
> The best way to discharge a HV cap is to
> connect a ~5kΩ across it. Don't use a small 1/4Watt resistor, you will
> just set it on fire! I use 5W ceramic resistors, but a 1W resistor is
> ok too. Don't hold it with you fingers, because there may voltages you
> don't want touch.
> Screwdriver discharge is NOT a good idea at all. It can damage the cap
> and it can blow other devices (I used a screwdriver some time ago and
> blew a TV set's control logic beyond repair).
While a resistor discharge is gentler, for the vast majority of
electrolytics (not photoflash, and not *coupling* capacitors),
discharge by shorting is fine, particularly when discharging a
bridging capacitor that is no longer connected to a circuit.
The biggest issue with a bridging capacitor is that it is being
bridged across various capacitors (I usually do it using test
leads without removing power), and you don't want to carry a
higher voltage charge to a capacitor operating at a lower voltage,
in general--so it's good to discharge it by shorting between
bridging operations. I will usually bridge a half-dozen capacitors
in minute or so while watching the display for change!
(My first for-pay job was working in a TV repair shop, and speed
was of the essence. If I spent more than 40 minutes fixing a set,
including disassembly and reassembly, I was regarded as slow! ;-)
Most electrolytics are serving as filter or bypass capacitors, and
one side is generally at circuit-ground. It's hard to damage a
circuit by discharging one of these by shorting.
A few electrolytic capacitors are used to block DC in a coupling
role, and shorting one of these while still in the circuit can
apply the blocked voltage to an input unable to handle it.
I agree that if a capacitor is to be discharged *in circuit*, and
its role is unknown, a softer, gentler discharge is preferable.
>>I must admit, apart from the two largest caps (one of which required
>>the removal of metal shielding), the other caps have been relatively
>>simple to desolder, so I'm happy enough to keep going that way for
>>now.
>>
>>
>
> This is better anyway. I've had many electrolytics which became leaky
> (electrically speaking...)
An electrically "leaky" capacitor in a coupling role is a problem,
but in a bypass or filter role, it may go unnoticed unless it becomes
progressive and results in an overheating or shorted cap.
>>>>If the problem is still present after replacing all the high voltage
>>>>caps, is it worthwhile continuing replacing the lower voltage
>>>>electrolytics, or should I start suspecting something else as the
>>>>failure?
>>
> I'd suspect C514, C601 and C607 (which could be left out for testing).
>
>
>>>Using the bridging technique really lowers the penalty for checking
>>>out most of the other capacitors, and electrolytics are still the
>>>most likely failure candidates.
>>
> But you'll have for a warm-up every time.
In fact, using a hair dryer can provide some localization for the
problem--particularly if used in alternation with a cooling spray.
(Careful about high voltages, of course.)
>>The symtoms are as follows: when the monitor is first switched on, the
>>contrast / brightness is quite low but the picture is nice and sharp.
>>By turning the up brightness / contrast a little, you get quite a good
>>image. However, after about 10 minutes the monitors picture starts
>>getting noticeably brighter and continues to do so. After about 30
>>minutes, the image has become really bright and the focus has degraded
>>to a point that hurts your eyes. Lowering the brightness / contrast
>>doesn't help as the image is all blurry and very hard on the eyes. If
>>you look back through the history of this thread, I posted one of the
>>Apple II FAQ questions and answers which sounds remarkably like what
>>I'm seeing - this is what started me replacing "filter" capacitors.
>>
>
> I don't really believe this is a filter capacitor problem.
I agree. The temperature-dependency argues for either a leaky
non-electrolytic in the HV/focus area, or a faulty resistor in
the same area.
I agree. The fault will be something common to all three guns.
> BTW: Many monitors have voltages printed next to some points
> (especially connectors). Check these!
> If you know where to look for the fault then you can trace the wires
> and replace the caps you find on the way.
>
> If the divider is bad, you're in trouble. These are not easily
> obtainable and very expensive. The only sensible repair would be to
> get another flyback transformer and transplant the HV divider.
> This procedure is decribed in the Repairfaq as "Focus/Screen divider
> bypass surgery".
Exact replacements for older gear are always a problem. I haven't
looked at the physical arrangement, but it may be possible to use
discrete high-voltage resistors/pots to bypass part of the divider
or re-create it. If space is tight, this may require potting. ;-(
Polymorph
> In fact, using a hair dryer can provide some localization for the
> problem--particularly if used in alternation with a cooling spray.
> (Careful about high voltages, of course.)
>
>
> I agree. The temperature-dependency argues for either a leaky
> non-electrolytic in the HV/focus area, or a faulty resistor in
> the same area.
I have two expert opinions pretty much agreeing with each another.
Does this mean I should abandon the electrolytic capacitor replacement
and concentrate on the area's you guys have mentioned? Is the HV/focus
area where the 240V (I'm in Australia) power supply is, or is it
around the flyback transformer? I'm still not up with all of the
terminology being used. I hope its something simple as a non-
electrolytic cap or dodgy resistor. What is the best method for
determining which one is faulty? Replacing the components with those
from the known good monitor? Some more info on where to start looking
would be great.
The problem with my monitor is starting to sound more serious than I
had hoped. I don't want to have to fork out a lot of money trying to
get this operational again - particularly considering that I'm so
green at doing this kind of work and probably more than a little out
of my comfort zone. I'll keep trying your suggestions for now, but i
If things can not be resolved after doing this, I may have to give up
and start looking for an alternative monitor. :-(
But I really appreciate all of the effort made in assisting me. :-)
Thanks,
Mike
Michael J. Mahon
> On Jan 7, 7:15 am, "Michael J. Mahon" <mjma...@aol.com> wrote:
>
>>In fact, using a hair dryer can provide some localization for the
>>problem--particularly if used in alternation with a cooling spray.
>>(Careful about high voltages, of course.)
>>
>>
>>>I don't really believe this is a filter capacitor problem.
>>
>>I agree. The temperature-dependency argues for either a leaky
>>non-electrolytic in the HV/focus area, or a faulty resistor in
>>the same area.
>
>
> I have two expert opinions pretty much agreeing with each another.
> Does this mean I should abandon the electrolytic capacitor replacement
> and concentrate on the area's you guys have mentioned? Is the HV/focus
> area where the 240V (I'm in Australia) power supply is, or is it
> around the flyback transformer? I'm still not up with all of the
> terminology being used. I hope its something simple as a non-
> electrolytic cap or dodgy resistor. What is the best method for
> determining which one is faulty? Replacing the components with those
> from the known good monitor? Some more info on where to start looking
> would be great.
It's in the area of the flyback transformer. The focus and screen
controls and the associated voltage divider are there, in the same
plastic assembly, I presume.
It may still turn out not to be too hard to fix--just different from
what was expected. ;-)
Polymorph
> It may still turn out not to be too hard to fix--just different from
> what was expected. ;-)
Well, I'm glad I didn't give up so soon as I am rather happy and (a
little embarassed to find that the solution was so easy) to say that
the problem did appear to be the HV divider. After allowing the
monitor to warm up (approx. 20 - 30 mins), I then adjusted the pots as
Ferdinand described and was able to get a good picture (both focus and
brightness). I left the monitor running for quite a while and it
seemed to keep the brightness and focus settings.
I switched off and unplugged the monitor overnight and retested this
morning. After a brief warm up period (say 30 seconds) the image
became visable with good contrast and focus.
I will do some more testing tonight to determine if this has fully
fixed the problem. I have only been running the monitor with the
textual IIgs startup screen (the one with the Apple flying backwards
and forwards) as I removed all of my prized expansion cards from the
IIgs before testing. When I fire up GS/OS it will give a better
indication of the clarity due to the higher resolution, but from what
I'm seeing, I'm pretty confident it will be OK.
Now if only I had the knowledge to have tried this sooner, I could
have avoided inhaling all of the solder fumes (yes I am aware they are
not good for you and I do avoid them as much as possible!). You live
and you learn.
So it would seem that the components in my monitor are not faulty,
just the technician. ;-)
I'll post back tonight when I get around to doing further testing...
Thanks guys, my daughter will be pleased to get her computer
operational again.
Cheers,
Mike
Michael J. Mahon
> On Jan 7, 1:24 pm, "Michael J. Mahon" <mjma...@aol.com> wrote:
>
>>It may still turn out not to be too hard to fix--just different from
>>what was expected. ;-)
>
>
>
> Well, I'm glad I didn't give up so soon as I am rather happy and (a
> little embarassed to find that the solution was so easy) to say that
> the problem did appear to be the HV divider. After allowing the
> monitor to warm up (approx. 20 - 30 mins), I then adjusted the pots as
> Ferdinand described and was able to get a good picture (both focus and
> brightness). I left the monitor running for quite a while and it
> seemed to keep the brightness and focus settings.
>
> I switched off and unplugged the monitor overnight and retested this
> morning. After a brief warm up period (say 30 seconds) the image
> became visable with good contrast and focus.
This sounds like a case of what would be called "pot noise" if it
were an audio application. When a pot is seldom changed, the sliding
contact with the carbon element can become dirty/imperfect, and, in
some cases, temperature- or stress-sensitive.
In most of these cases, simply turning the pot several times back and
forth over the normal set point will clean the contact and element and
restore normal function. In extreme cases, use of a specialized cleaner
is called for.
I'm glad that you got it working!
> I will do some more testing tonight to determine if this has fully
> fixed the problem. I have only been running the monitor with the
> textual IIgs startup screen (the one with the Apple flying backwards
> and forwards) as I removed all of my prized expansion cards from the
> IIgs before testing. When I fire up GS/OS it will give a better
> indication of the clarity due to the higher resolution, but from what
> I'm seeing, I'm pretty confident it will be OK.
>
> Now if only I had the knowledge to have tried this sooner, I could
> have avoided inhaling all of the solder fumes (yes I am aware they are
> not good for you and I do avoid them as much as possible!). You live
> and you learn.
They can't be too bad for you--I've breathed them (just incidentally)
for years and I'm not dead yet. ;-)
Seriously, lead vapor is a potential issue, but the vapor pressure
of lead is quite low at the melting point of solder. A fume hood
is not justified.
> So it would seem that the components in my monitor are not faulty,
> just the technician. ;-)
;-) Many times I have made the same observation about myself! ;-)
> I'll post back tonight when I get around to doing further testing...
>
> Thanks guys, my daughter will be pleased to get her computer
> operational again.
Good for you, for sticking with it and being willing to experiment.
Polymorph
OK, my daughter has been playing on her IIgs for about an hour now. The
monitor still does have a problem, but it is much easier to live with
now. It still does get gradually brighter, but due to the adjustments I
made last night, you can get a reasonable picture by just adjusting the
side controls (i.e. you don't need to open the case). It has only lost a
little focus and is still readable at this stage.
It would seem if I wanted this monitor to be 100% I would need to spend
more time on it - and I aim to do that when I can get a replacement
monitor (I have a replacement monitor in my sights courtesy of eBay).
But it seems fairly obvious the problem is in the HV/flyback transformer
area.
The problem does appear to be heat related, as it is now running with
the case on, whereas last night it was running with the case off and
probably heated slower because of this.
If you were to keep investigating, how would you order, in likelihood of
success, the following potential fixes:
* replace electrolytic capacitors in the HV area?
* replace non-electrolytic capacitors in the HV area?
* replace resistors in the HV area?
* something else?
Thanks,
Mike
--- Synchronet 3.14a-Win32 NewsLink 1.85
A2Central.com - Your total source for Apple II computing.
gr...@comcast.net
Hi,
The fumes might have been mostly rosin, not that is good for you or
any better.
I would have tried to cool down compents before I replaced them. That
is I would run the monitor for hours to heat it up for the problem to
come up. Then shut it down then spray a component with one of the
cooling agents. Just enough to bring it down. Not enough to cause
frost, if there is enough moisture in the air.
Then I might have tried replacing whole boards if I was not sure,
rather the components. Which takes a longer time. Once a board
replacement fixes the problem. Then component replacement would start.
Take Care
fer...@gmx.de
this> wrote:
> To: Michael J. Mahon
>
>
>
> Michael J. Mahon wrote:
> > Polymorph wrote:
> >> On Jan 7, 1:24 pm, "Michael J. Mahon" <mjma...@aol.com> wrote:
>
> >>> It may still turn out not to be too hard to fix--just different from
> >>> what was expected. ;-)
>
> >> Well, I'm glad I didn't give up so soon as I am rather happy and (a
> >> little embarassed to find that the solution was so easy) to say that
> >> the problem did appear to be the HV divider. After allowing the
> >> monitor to warm up (approx. 20 - 30 mins), I then adjusted the pots as
> >> Ferdinand described and was able to get a good picture (both focus and
> >> brightness). I left the monitor running for quite a while and it
> >> seemed to keep the brightness and focus settings.
>
>
> It would seem if I wanted this monitor to be 100% I would need to spend
> more time on it - and I aim to do that when I can get a replacement
> monitor (I have a replacement monitor in my sights courtesy of eBay).
> But it seems fairly obvious the problem is in the HV/flyback transformer
> area.
>
> The problem does appear to be heat related, as it is now running with
> the case on, whereas last night it was running with the case off and
> probably heated slower because of this.
>
> If you were to keep investigating, how would you order, in likelihood of
> success, the following potential fixes:
> * replace electrolytic capacitors in the HV area?
> * replace non-electrolytic capacitors in the HV area?
> * replace resistors in the HV area?
> * something else?
>
it. The problem is extremely likely to be with the focus/screen pots.
You should concentrate on this. There is only one cap which could
affect brightness, bot it would not affect focus and it would only be
able to REDUCE the brightness. The HV divider can usually not be
replaced, you'd have to replace the whole flyback assembly, which
can't be done at reasonable cost, if at all.
But there are other possible fixes:
- turn the pots back and forth very rapidly (10 times or so) . After
that, turn the monitor on with SCREEN at minimum and readjust.
- live with it (perhaps set up the focus with a warm monitor)
- leave the case off (not a good idea for your daughter...)
- install a cooling fan
- drill two holes into the case to allow adjustment from the outside
- attach an external divider.
Ferdinand
Polymorph
> Something else: It looks like you have found the problem so stick to
> it. The problem is extremely likely to be with the focus/screen pots.
> You should concentrate on this. There is only one cap which could
> affect brightness, bot it would not affect focus and it would only be
> able to REDUCE the brightness. The HV divider can usually not be
> replaced, you'd have to replace the whole flyback assembly, which
> can't be done at reasonable cost, if at all.
> But there are other possible fixes:
> - turn the pots back and forth very rapidly (10 times or so) . After
> that, turn the monitor on with SCREEN at minimum and readjust.
> - live with it (perhaps set up the focus with a warm monitor)
> - leave the case off (not a good idea for your daughter...)
> - install a cooling fan
> - drill two holes into the case to allow adjustment from the outside
> - attach an external divider.
Thanks for your tips Ferdinand, I'll most definately give them a try.
It looks likely that I will be able to source another Amiga monitor in
the next few days, so if I do I will decomission the AppleColor and
spend some more time trying to get it working 100%.
I think I may send the old Amiga monitor (the one that died
originally) to the monitor home in the sky, as I don't think its worth
the effort/cost in fixing, especially if I can get a cheap
replacement. I may spend a little more time on it looking for anything
obviously wrong, but other than that, I think it will go.
By the way, it has become pretty obvious during the course of
performing this repair that the Apple II Monitor FAQ may require some
revising. As I stated in an earlier post, one of the suggested
solutions to a problem sounding very much like mine was to replace the
filter capacitors. Now, it would seem that performing this action
would do very little to fixing this problem (as I found out the hard
way). Does this sound like a fair comment, or is it just that my
problem was a little different from the "normal" problems associated
with this monitor?
Maybe with some agreement from you experts, we could have it revised
to include some alternative solutions. This will probably be more and
more relevant as time goes on, as more and more monitors will begin to
fail.
What do you think?
Thanks,
Mike
Michael J. Mahon
> On Jan 9, 1:10 am, ferd...@gmx.de wrote:
>
>>Something else: It looks like you have found the problem so stick to
>>it. The problem is extremely likely to be with the focus/screen pots.
>>You should concentrate on this. There is only one cap which could
>>affect brightness, bot it would not affect focus and it would only be
>>able to REDUCE the brightness. The HV divider can usually not be
>>replaced, you'd have to replace the whole flyback assembly, which
>>can't be done at reasonable cost, if at all.
>>But there are other possible fixes:
>> - turn the pots back and forth very rapidly (10 times or so) . After
>>that, turn the monitor on with SCREEN at minimum and readjust.
>> - live with it (perhaps set up the focus with a warm monitor)
>> - leave the case off (not a good idea for your daughter...)
>> - install a cooling fan
>> - drill two holes into the case to allow adjustment from the outside
>> - attach an external divider.
>
>
> Thanks for your tips Ferdinand, I'll most definately give them a try.
I agree with his suggestions.
> It looks likely that I will be able to source another Amiga monitor in
> the next few days, so if I do I will decomission the AppleColor and
> spend some more time trying to get it working 100%.
>
> I think I may send the old Amiga monitor (the one that died
> originally) to the monitor home in the sky, as I don't think its worth
> the effort/cost in fixing, especially if I can get a cheap
> replacement. I may spend a little more time on it looking for anything
> obviously wrong, but other than that, I think it will go.
Don't overlook the advantage of having an identical working version
of a device. You can measure various points in the circuit on the
good one and compare them with the bad one to localize the problem.
This method does require knowing what circuits can cause other
circuits to behave abnormally, however. (That is what is complicated
so much by feedback--it couples the whole loop together so a failure
anywhere in it affects the whole thing.)
> By the way, it has become pretty obvious during the course of
> performing this repair that the Apple II Monitor FAQ may require some
> revising. As I stated in an earlier post, one of the suggested
> solutions to a problem sounding very much like mine was to replace the
> filter capacitors. Now, it would seem that performing this action
> would do very little to fixing this problem (as I found out the hard
> way). Does this sound like a fair comment, or is it just that my
> problem was a little different from the "normal" problems associated
> with this monitor?
Many repair FAQs have the problem of being created from sparse anecdotal
evidence, so the true range of causes and their probabilities are not
well described.
In this situation, simply collecting the anecdotes may be the right
way to go.
> Maybe with some agreement from you experts, we could have it revised
> to include some alternative solutions. This will probably be more and
> more relevant as time goes on, as more and more monitors will begin to
> fail.
>
> What do you think?
Good point. So far, I haven't had any AppleColor RGBs fail, but I don't
use them much, so I'm not a good example. All of my suggestions come
from general monitor and TV repair experience, which is not nearly as
useful as deep experience with a particular monitor design. ;-)
fer...@gmx.de
> By the way, it has become pretty obvious during the course of
> performing this repair that the Apple II Monitor FAQ may require some
> revising. As I stated in an earlier post, one of the suggested
> solutions to a problem sounding very much like mine was to replace the
> filter capacitors. Now, it would seem that performing this action
> would do very little to fixing this problem (as I found out the hard
> way). Does this sound like a fair comment, or is it just that my
> problem was a little different from the "normal" problems associated
> with this monitor?
>
brightness and bad focus which gets better. This indeed can be caused
by bad caps.
But you problem is not normal. HV divider problems are usually more
erratic, and this is also said in the FAQ.
> Maybe with some agreement from you experts, we could have it revised
> to include some alternative solutions. This will probably be more and
> more relevant as time goes on, as more and more monitors will begin to
> fail.
>
> What do you think?
There will be another problem coming up: Even if we are able to keep
the electronics running we can't stop the picture tube's aging
process.
Sooner or later the picture will be dim and blurry.
We really need to watch out for alternatives. Maybe transplants are
possible, but we should watch out for replacement monitors.
If you live in Europe, you can use your TV-set because they're fitted
with SCART connectors here. And most picture tubes used in PAL TV sets
are even sharp enough for the 80-column-mode.
One could add RGB inputs to a TV-set, or one could try to convert RGB
to YUV and connect it to a TV-set.
I'm working on a VGA adapter board for the //e, but I don't think this
can be adapted for a GS. It would be possible if there's digital RGB
video available.
Sooner or later we'll have to use LCD monitors on our good old Apple ]
[ gear.
Ferdinand (who hopes that his 23'' CRT monitor will last forever)
Jerry
> There will be another problem coming up: Even if we are able to keep
> the electronics running we can't stop the picture tube's aging
> process.
> Sooner or later the picture will be dim and blurry.
>
> We really need to watch out for alternatives. Maybe transplants are
> possible, but we should watch out for replacement monitors.
> If you live in Europe, you can use your TV-set because they're fitted
> with SCART connectors here. And most picture tubes used in PAL TV sets
> are even sharp enough for the 80-column-mode.
> One could add RGB inputs to a TV-set, or one could try to convert RGB
> to YUV and connect it to a TV-set.
> I'm working on a VGA adapter board for the //e, but I don't think this
> can be adapted for a GS. It would be possible if there's digital RGB
> video available.
> Sooner or later we'll have to use LCD monitors on our good old Apple ]
> [ gear.
I recently bought a Benq FP241W LCD monitor since my old Dell 19" CRT was
dying. This new monitor has all sorts of inputs, including an NTSC RCA
jack, plus individual R, G, and B RCA inputs. I haven't tried my IIgs on
it yet, but an Apple IIc works quite well. There is a very slow roll to
the image, but it's quite usable even in 80-column mode. So, this is
certainly an option for today and a few years into the future, and it
requires no additional hardware if you use the NTSC output on your Apple
II. I will have to try a cable from the IIgs to the RGB inputs on the LCD
panel sometime.
--
-- Jerry
Polymorph
> I recently bought a Benq FP241W LCD monitor since my old Dell 19" CRT was
> dying. This new monitor has all sorts of inputs, including an NTSC RCA
> jack, plus individual R, G, and B RCA inputs. I haven't tried my IIgs on
> it yet, but an Apple IIc works quite well. There is a very slow roll to
> the image, but it's quite usable even in 80-column mode. So, this is
> certainly an option for today and a few years into the future, and it
> requires no additional hardware if you use the NTSC output on your Apple
> II. I will have to try a cable from the IIgs to the RGB inputs on the LCD
> panel sometime.
Great Jerry! Let us know how it goes with the IIgs RGB signal. I for
one will be interested in hearing your results.
I know mid-way through last year, an announcement was made that work
was being done in conjunction with GSE-Reactive to come up with a
means of converting the IIgs RGB signal into something usable by
modern day monitors. I haven't heard anything recently, but I presume
this work is still being carried out?
I agree that this will have to be done sometime soon. Even if we can
keep our monitors running for a few more years, I'm guessing that most
will not be as sharp as they once were. So for our eyes sake alone,
the benefits would be great. Not to mention the reduced power
consumption, smaller footprints on our desktop, maybe allowing the
sharing of a monitor, etc, etc...
I think this will prove to be one of the biggest advancements in
recent times for the Apple II if/when it eventuates. I know it might
not be a truly retro solution, but IMHO the advantages outweigh the
negatives.
Cheers,
Mike
Michael J. Mahon
> I recently bought a Benq FP241W LCD monitor since my old Dell 19" CRT was
> dying. This new monitor has all sorts of inputs, including an NTSC RCA
> jack, plus individual R, G, and B RCA inputs. I haven't tried my IIgs on
> it yet, but an Apple IIc works quite well. There is a very slow roll to
> the image, but it's quite usable even in 80-column mode.
What, exactly, is a "very slow roll to the image."
Does the image position change on the monitor? Does a small "ripple"
move through it? I'd like to know more.
fer...@gmx.de
> Jerry wrote:
> > I recently bought a Benq FP241W LCD monitor since my old Dell 19" CRT was
> > dying. This new monitor has all sorts of inputs, including an NTSC RCA
> > jack, plus individual R, G, and B RCA inputs. I haven't tried my IIgs on
> > it yet, but an Apple IIc works quite well. There is a very slow roll to
> > the image, but it's quite usable even in 80-column mode.
>
> What, exactly, is a "very slow roll to the image."
>
> Does the image position change on the monitor? Does a small "ripple"
> move through it? I'd like to know more.
>
1) The whole picture rolls very slowly as if it was out-of-sync.
2) The picture rolls 1/4 to 3/4 over the screen, then jumps to the
original position where it starts to roll again
3) The picture jumps up and down very rapidly.
I've seen all of these on different digital displays.
1 happens on my TV capture card with a bt878 chipset.
2 happened on a video projector.
3 is seen very often. Had it on a 100Hz Doublescan-TV, many video
projectors and TV capture cards.
All these are very often caused by the lack of interlacing in the
Apple ][s video output causing the decoder which actually counts the
lines not to sync properly.
This can sometimes be remedied by using a setting like "Old game" or
"Still display".
The only real fix would be to reprogram the video DSP...
Ferdinand
Michael J. Mahon
> On 10 Jan., 21:29, "Michael J. Mahon" <mjma...@aol.com> wrote:
>
>>Jerry wrote:
>>
>>>I recently bought a Benq FP241W LCD monitor since my old Dell 19" CRT was
>>>dying. This new monitor has all sorts of inputs, including an NTSC RCA
>>>jack, plus individual R, G, and B RCA inputs. I haven't tried my IIgs on
>>>it yet, but an Apple IIc works quite well. There is a very slow roll to
>>>the image, but it's quite usable even in 80-column mode.
>>
>>What, exactly, is a "very slow roll to the image."
>>
>>Does the image position change on the monitor? Does a small "ripple"
>>move through it? I'd like to know more.
>>
>
> I think it is one of these:
> 1) The whole picture rolls very slowly as if it was out-of-sync.
> 2) The picture rolls 1/4 to 3/4 over the screen, then jumps to the
> original position where it starts to roll again
> 3) The picture jumps up and down very rapidly.
> I've seen all of these on different digital displays.
Yes, those are all possibly described as "roll" (though 1 and 2 are
the most likely)--but I would find that any of these behaviors would
render the display completely unusable.
> 1 happens on my TV capture card with a bt878 chipset.
> 2 happened on a video projector.
> 3 is seen very often. Had it on a 100Hz Doublescan-TV, many video
> projectors and TV capture cards.
>
> All these are very often caused by the lack of interlacing in the
> Apple ][s video output causing the decoder which actually counts the
> lines not to sync properly.
> This can sometimes be remedied by using a setting like "Old game" or
> "Still display".
> The only real fix would be to reprogram the video DSP...
Right. It's a shame that digital TVs have become so intolerant
of distorted or non-standard signals. It's not really that hard
to make the sync algorithm adaptive...
I still remember the original RCA 630TS color receiver--it would
sync solidly to a signal with such low signal-to-noise ratio that
you could barely make it out in the "snow"! Of course, it had 30
tubes, too. ;-)
"Analog emulation" would be a nice mode for digital TVs. ;-)
fer...@gmx.de
>
> Right. It's a shame that digital TVs have become so intolerant
> of distorted or non-standard signals. It's not really that hard
> to make the sync algorithm adaptive...
>
> I still remember the original RCA 630TS color receiver--it would
> sync solidly to a signal with such low signal-to-noise ratio that
> you could barely make it out in the "snow"! Of course, it had 30
> tubes, too. ;-)
>
> "Analog emulation" would be a nice mode for digital TVs. ;-)
>
sync problems.
BTW, Grundig used analog sync and color decoders before a digital
double-scan is performed...
This yields a picture quality I've never seen on a double-scan TV.
I don't think an analog sync decoder is very expensive.
BTW, why do many color TVs choose the color system based on the
vertical refresh rate?! I have seen that many times with a multisystem
TV on a 50Hz Apple. If it is forced to NTSC it will work. Otherwise it
won't.
Another think is the extreme sensivity of today's color TVs. Why did
they turn it up that far?! The TV I use on the Apple ][ syncs to 10mV
color burst. The problem is, that such a low level is always present,
even in text mode. This will cause VERY annoying color patterns in
text mode, much worse than the little green/violet shadows. I solved
it by detuning the Apples oscillator so that the TV won't lock to it
anymore.
-------
Ferdinand
Michael J. Mahon
> On 10 Jan., 22:43, "Michael J. Mahon" <mjma...@aol.com> wrote:
>
>>Right. It's a shame that digital TVs have become so intolerant
>>of distorted or non-standard signals. It's not really that hard
>>to make the sync algorithm adaptive...
>>
>>I still remember the original RCA 630TS color receiver--it would
>>sync solidly to a signal with such low signal-to-noise ratio that
>>you could barely make it out in the "snow"! Of course, it had 30
>>tubes, too. ;-)
>>
>>"Analog emulation" would be a nice mode for digital TVs. ;-)
>>
>
> Not a good idea... They would blur the picture and wouldn't fix their
> sync problems.
Sync emulation is part of the emulation--it would work fine if
there were any DSP engineers today who understood how TV sets
used to work. ;-)
> BTW, Grundig used analog sync and color decoders before a digital
> double-scan is performed...
> This yields a picture quality I've never seen on a double-scan TV.
> I don't think an analog sync decoder is very expensive.
It's easy in one chip, but that's an *extra* chip for a digital TV.
The DSP code is pretty straightforward, but it's extra code. It's just
cascaded RC filters and thresholding.
> BTW, why do many color TVs choose the color system based on the
> vertical refresh rate?! I have seen that many times with a multisystem
> TV on a 50Hz Apple. If it is forced to NTSC it will work. Otherwise it
> won't.
Because it's simple and the first idea that comes to mind. ;-(
> Another think is the extreme sensivity of today's color TVs. Why did
> they turn it up that far?! The TV I use on the Apple ][ syncs to 10mV
> color burst. The problem is, that such a low level is always present,
> even in text mode. This will cause VERY annoying color patterns in
> text mode, much worse than the little green/violet shadows. I solved
> it by detuning the Apples oscillator so that the TV won't lock to it
> anymore.
I think there is a spec for the level of burst required to switch to
color, but it would be easily ignored...
Michael Kent
> It's easy in one chip, but that's an *extra* chip for a digital TV.
Who are you and what have you done with Michael J. Mahon? The *real*
Michael Mahon wouldn't be so cavalier about adding an extra chip. ;-)
Mike
fer...@gmx.de
>
> Sync emulation is part of the emulation--it would work fine if
> there were any DSP engineers today who understood how TV sets
> used to work. ;-)
>
> > BTW, Grundig used analog sync and color decoders before a digital
> > double-scan is performed...
> > This yields a picture quality I've never seen on a double-scan TV.
> > I don't think an analog sync decoder is very expensive.
>
> It's easy in one chip, but that's an *extra* chip for a digital TV.
>
> The DSP code is pretty straightforward, but it's extra code. It's just
> cascaded RC filters and thresholding.
You need to convert it to an image of fixed size. That means the DSP
SHOULD
- sample the signal at a rate to get the right width (perhaps use a
PLL to get the clock from the Hsync, this could be integrated into the
HPLL)
- store it line by line, start a new field after either Vertical sync
or after a certain number of lines has passed (350 or so).
- check the position of the Vsync to find out whether this is an even
or odd field.
- if there is interlacing, deinterlace and scale by the factor needed
to fill the screen
- if not, scale every field to fill the screen.
This is not done too.
The algorithms I saw did something like the following:
- sample at an arbitrarily chosen frequency.
- scale it to the minimum needed to achieve the desired video
bandwith
- store it in memory with the expected number of lines. Go crazy if
it is wrong.
- Always interlace the fields. If there is no interlacing, interlace
anyway.
- Blur - eh denoise the picture
- Apply nonlinear scaling to allow certain special display modes.
- Scale it to the size needed.
This is from the data sheet of a Micronas video processing chipset I
wanted to use to get high-quality video display on a VGA monitor. I've
given up...
Ferdinand
Michael J. Mahon
;-)
That's why I punched *extra*--that's the kiss of death for a
consumer electronics designer. ;-)
It's *nice* if a CE device works, but it's *essential* that its
bill of materials is minimized. ;-)
Michael J. Mahon
Well, there are other ways of organizing the processing, but any
particular design will optimize for one or two expected modes of
processing and then "everything else" will be kludged in.
It would not be difficult to take an analog-based approach to sensing
sync, but I'd be very surprised if any monitor actually did it.
Of course, you should also make the determination about whether the
signal is interlaced or not--but since all "legitimate" NTSC signals
are interlaced, you can bet that the usual logic doesn't even consider
that to be a variable. (If the detected vertical sync occurs
alternately near the start of a line and near mid-line, then the signal
is interlaced--if always near the start of a line, then not interlaced.)
What you do with video processing after sync is determined is pretty
standard, and not very well suited to handling digitally generated
video with a "non-standard" pixel density--like Apple II video.
What would be needed to do a *good* job with digitally generated video
would be to (somehow) recover the dot clock from the video stream and
use that (or a multiple of it) to sample the video. I think at this
point, the liklihood of any commercial design taking this approach is
miniscule.
Jerry
> Jerry wrote:
>
>> I recently bought a Benq FP241W LCD monitor since my old Dell 19" CRT was
>> dying. This new monitor has all sorts of inputs, including an NTSC RCA
>> jack, plus individual R, G, and B RCA inputs. I haven't tried my IIgs on
>> it yet, but an Apple IIc works quite well. There is a very slow roll to
>> the image, but it's quite usable even in 80-column mode.
>
> What, exactly, is a "very slow roll to the image."
>
> Does the image position change on the monitor? Does a small "ripple"
> move through it? I'd like to know more.
I didn't describe it well. It's a very slow ripple in which the picture is
every so slightly shifted to the left or the right, I cannot remember which
direction. It's borderline noticeable; I was looking for such things.
I'll try to take a picture of it soon. When I do, I will let the group
know.
--
-- Jerry
Michael J. Mahon
I presume that the "ripple" is horizontal and moves slowly from top to
bottom or bottom to top.
This is most likely a beat between the power line frequency and the
vertical sync frequency of the Apple II. This would not be an issue
unless there is 60Hz power line noise getting into the signal or the
sync circuits of the monitor, causing a slight disruption of the phase
of detected horizontal sync.
You might try plugging both the monitor and the Apple into the same
electrical circuit (for example, on a power strip). You may also
want to check the tightness of the RCA plug outer connector on both
ends of the video cable, or try another cable.
If this does not fix the problem, it may result from power supply ripple
in either the Apple II or the monitor. If the line side rectifier is
half-wave, the ripple frequency would be 60Hz, causing a single area
of distortion per frame. If a full-wave rectifier, then there should
be two areas of distortion per frame, moving together up or down the
raster.
Ironically, the reason that 60Hz was picked for the vertical scan rate
of NTSC (and 50Hz for most PAL systems) was to allow the TV sync to be
locked to the local AC power frequency, causing distortions of the type
you observe to be immobile, and therefore less noticeable. Of course,
this became less useful as nationwide networks became prevalent, while
there is still no nationwide synchronization of several power grids in
the US.
With CRT displays, the biggest likely source of line frequency
interference was the stray magnetic field of the TV's power transformer
or other nearby appliances, but that cause is irrelevant today. ;-)