1084s monitor that needs fixing
Scott McCormack
that the picture is "dark" like the brightness was turned way down (of
course it isn't) anyone think this is something that is fixable? The picture
is fine other than that and the sound is perfect. I got this monitor with
my Colt PC-20 years ago and am in the process of trying to get my old
commodore stuff back in working shape and would love to use the monitor with
a 128 for 80col mode.
thanks
Scott
Professor Dredd
http://landru.myhome.net/rcarlsen/
Email: rcar...@myhome.net or rr...@u.washington.edu
"Scott McCormack" <pega...@attbi.com> wrote in message news:<PLap8.167829$q2.16392@sccrnsc01>...
Geoff Emery
electrical safety hooked it up to soak test and it ran beautifully for about
6hrs then the psu developed severe hiccoughing. Is there a list of common
faults available? I suspect faulty caps around the horizontal drive and have
downloaded copies of the schems to the hard drive but the piggy bank doesn't
run to shotgunning all the electros. Also have one running and another for
parts so would be interested in feedback like Scott.
Many thanks,
Geoff Emery
Scott McCormack <pega...@attbi.com> wrote in message
news:PLap8.167829$q2.16392@sccrnsc01...
mykrowyre
I think a dark screen is usually due to a leaking picture tube... I dont
know for sure but this is a symptom of old dying monitors from what I've
heard...
-tom
mike
writes:
>
>Just another query about 1084S. I picked one up and after checking
>electrical safety hooked it up to soak test and it ran beautifully for about
>6hrs then the psu developed severe hiccoughing. Is there a list of common
>faults available? I suspect faulty caps around the horizontal drive and have
>downloaded copies of the schems to the hard drive but the piggy bank doesn't
>run to shotgunning all the electros. Also have one running and another for
>parts so would be interested in feedback like Scott.
> Many thanks,
>
>Geoff Emery
>
As was mentioned already, Ray Carlson is the expert, but I would suspect bad
solder joints around the flyback xformer. They have a tendacy (sp) to go bad
due to heat.
Mike
University Place Commodore User Group (UPCHUG)
Raymond Carlsen
> except that the picture is "dark" like the brightness was turned way down
> (of course it isn't) anyone think this is something that is fixable? The
> picture is fine other than that and the sound is perfect.
Scott,
I don't normally recommend adjusting things to fix a problem, but in
this case, see what effect turning up the master screen control has. It's
the lower control on the flyback (line output transformer), the upper one
being focus. What does the picture look like with increased brightness?
Does the user brightness control work normally? See if bumping the monitor
has any effect on the screen image. Get back to me with the results and
we'll go from there.
Ray
Raymond Carlsen
> electrical safety hooked it up to soak test and it ran beautifully for about
> 6hrs then the psu developed severe hiccoughing.
Geoff,
You'll need to describe it better. Does the monitor work, but produce
strange noises, or does it not work at all but just "tick" repeatedly?
> Is there a list of common faults available?
Only in my head. :-) Gotta get a handle on what it's doing first.
> I suspect faulty caps around the horizontal drive and have downloaded
> copies of the schems to the hard drive but the piggy bank doesn't run to
> shotgunning all the electros.
No need, usually. Most problems with Commodore monitors are mechanical
intermittants caused by bad solder on the boards. When I get one on the
bench, the first thing I do (no matter the problem) is to rework all the
bad solder joints. If left too long with intermittants, parts start
failing. Start with the flyback (LOPT), H driver transformer, all power
transistors and diodes, any resistor of 1 Watt or more... anything that
generates heat in normal operation. If the PS is ticking, that usually
means it's overloaded and going into failsafe mode. Check the horizontal
output transistor for C to E shorts. Intermittant solder could have taken
it out... but so could a bad yoke or flyback. Gotta start somewhere. Go for
the soldering, and get back to me with symptoms.
Ray
Scott McCormack
I tried a few things and was able to restore the picture, but not
perminantly. The user brightness controls are working just fine, in fact the
monitor was turned up all the way so that the black background of the screen
looked grey. However at the same time normal color tones looked dark; flesh
tones looked dark orange etc. I tried turning contrast and brightness knobs
and the monitor responded so I smacked it lightly on the right side about
half way down the case. A bright flash came up on the screen then it went
back to it's dark state so I tapped the monitor again and POOF the picture
came up normally! It stayed that way untill I turned the monitor off. When I
turned it back on I had to whack it again before I got a normal picture. I
am going to hook it up to a cable box later and see if it'll really stay
working until I turn it off. One wierd thing about this monitor that it has
always done since the day I bought it. It never warmed up like other
displays it would always have a black screen then all of the sudden the
picture would instantly fade in fully bright. I always thought it was an odd
way to warm up for a monitor but it always worked, and interestingly enough
when it is working the picture is perfect. It's actually much sharper than
my 25 inch tv set. :)
Any ideas on how to fix the problem I assume that it is fixable since it
just takes a tap to make it work. I really can't do the work myself since I
am a mechanical idiot (i'm laible to break it trying to fix it. :)) Is there
anyone who knows of a shop in the San Francisco bay area that is able and
willing to work on these things? I've asked around but most places just look
at the monitor, roll their eyes and say "it's old, get a new one"
Thanks
Scott
"Raymond Carlsen" <rr...@u.washington.edu> wrote in message
news:Pine.A41.4.44.020331...@homer05.u.washington.edu...
Raymond Carlsen
> just takes a tap to make it work.
Scott,
Because it did that ever since it was new, it sounds more like a crack
in the PC board or perhaps a connection never soldered and/or just barely
making contact. If the tube is nice and bright when it is working, it's
certainly worth fixing. If it had been used a lot and the tube was tired, I
would say forget it. Whoever works on it is looking for an intermittant
that can be located by tapping on the board, so they will not need a
schematic. Just pull it apart and examine the board under strong light.
You'd be surprised how many times just a good physical exam will spot a
problem. If that doesn't show an obvious fault, they will have to run it
while apart and tap or flex the board to narrow the search to a specific
area, then to the intermittant itself. A board crack can be repaired with
super glue and the broken foil traces repaired with bare wire jumpers
soldered across the breaks. One last possibility is an intermittant picture
tube, but those usually progress to being unuseable rather quickly.
Ray
Professor Dredd
the same symptom ... when you tap the left side the picture comes
back. Be VERY CAREFUL about tapping the monitor though. I hit the side
of my 1902 a little too hard so the spring (clip thing) which holds
the speaker in place flew off and shorted out the PCB! :(
As always, working on CRTs is dangerous business. There's enough
residual charge in that monitor to kill you. The charge can linger for
a long time, even with the monitor unplugged (or so I was taught).
Raymond Carlsen <rr...@u.washington.edu> wrote in message news:<Pine.A41.4.44.020331...@homer08.u.washington.edu>...
Overdoc
Scott McCormack schrieb in Nachricht ...
>I have a 1084s monitor that I would love to get fixed
Well, I got 2 1084 monitors that I too would like to get fixed.
The first one suddenly went black with a blopping sound, while the power-led
went dark and the psu produced a whistling noise.
When it is turned on now there is no picture but just that whistling noise
:( Also the led doesn't come up any more.
I have already inspected the flyback for bad solder joints, but they appear
to be good.
I was told such symptoms could come from a overloaded psu due to a shorted
flyback. But how can I test the flyback ? The one in my 1084S seems a little
bit different than the one from the schematics.
Any help on this one, perhaps ?
The other 1084 ( no 's' ) doesn't do anything ( no picture, no sound ), but
the power led come up. I once swapped the psu from the other 1084 into this
one, but that didn't change anything :(
I hope there is nothing wrong with the flybacks of both monitors, because my
1084 have slightly different flybacks in them. So I could swap parts from
one to the other, except for the flybacks....
If anyone could give me a hint on where to start repairing these I would be
very grateful !
Reini
Raymond Carlsen
> one suddenly went black with a blopping sound, while the power-led went
> dark and the psu produced a whistling noise. When it is turned on now
> there is no picture but just that whistling noise :( Also the led doesn't
> come up any more. I have already inspected the flyback for bad solder
> joints, but they appear to be good. I was told such symptoms could come
> from a overloaded psu due to a shorted flyback. But how can I test the
> flyback?
Reini,
Although it could be a bad flyback, more than likely something else
failed. When a fly fails, you usually see the picture pull in from the
sides and fade out... sometimes with a burning smell from inside. In this
case, I would still check the H output transistor. It's on a heat sink near
the flyback. They normally fail collector to emitter, so an ohm meter
reading is a good enough test for that. It should measure like a diode one
way and nearly open (the charging of the input filter cap) the other way.
Zero ohms is shorted. Remove it and check again for transistor or circuit
short. Like a fuse, a transistor doesn't normally fail on its own but from
an overload. I would go over all the typical solder points, even though
they look OK, to ensure reliability. That includes the flyback, H driver
transformer, power transistors and diodes, and all resistors of 1 Watt or
more. Inspect the board under bright lights and magnification, then move
the light and look again from a different angle. Some flaky solder joints
are hard to see. Look for components on the board that may have overheated
(resistors burned or discolored, cracked diodes, etc). Follow up anything
unusual you find. Shorted diodes on the secondary side of the fly will burn
their fuse-resistors open as will any other short on a supply line.
> The flyback in my 1084S seems a little bit different than
> the one from the schematics. Any help on this one, perhaps ?
Try the 1902A (same as a 1084) and the other versions of the 1084 on my
site. You'll want an close schematic to use for troubleshooting.
> The other 1084 ( no 's' ) doesn't do anything ( no picture, no sound ),
> but the power led come up. I once swapped the psu from the other 1084
> into this one, but that didn't change anything :(
The power LED is driven off the power supply, not the fly, so as long
as it's not in overload shutdown, all outputs should be up. Sniff around
for any burned components. Does the picture tube "crackle" with high
voltage when you power it up? Put the back of your hand against the tube
face to feel for static electricity as you power on. That tells you whether
the HV is coming up at least. Look for the orange glow of the picture tube
filaments (driven off the flyback). If you have no high voltage (and no
filament voltage) and there are no burned components or blown fuses, look
for an -open- circuit rather than a short... (bad solder connections, crack
in the board). Check for B+ on the collector of the horizontal output
transistor. If there is +120VDC there but no high voltage, the H driver
circuit is not working. Look for B+ on the driver collector... and go from
there. If you feel the HV come up and die out quickly, the problem may be
excessive HV and the monitor is going into shutdown. That's a different
problem and harder to tackle. Let me know what you find with these checks.
Ray