need help with odd CRT monitor image

[mhoo...@gmail.com]

ive got a tovis mtg-1901cn cga color monitor. in use, or with a test pattern, the image starts out perfectly at the top. as you move down toward the middle , it gradually starts to compress the image, with more compression the closed you get to center. and when it gets to mid screen, its a full vertical collapse. bright while line across the center, with no image whatsoever in the lower 50% of the screen. also sold as a vision pro .

battery voltage is good at 123, 12v and 24 v are good. 123 volts at the flyback.
the vertical output ic is a LA7833. pin 6 has good 24 volt supply, and pin 2 ( output) is a nice 24 v square wave. i recapped the monitor, and the image is exactly the same. now im stuck.

thanks

[John-Del]

Sounds like a shorted turn in the deflection yoke, but not sure what you mean by a square wave on the output.

[John Robertson]

Your vertical circuit is missing the bottom deflection half of the
vertical circuit. If the vertical driver is an IC, replace it, if it is
a pair of transistors then I would suspect the transistor pulling to
ground (typically the lower of the two on schematics) is the one at fault.

The vertical drive is just a very slow audio amp, apply audio amp
service methods.

John :-#)#

--
(Please post followups or tech inquiries to the USENET newsgroup)
John's Jukes Ltd.
MOVED to #7 - 3979 Marine Way, Burnaby, BC, Canada V5J 5E3
(604)872-5757 (Pinballs, Jukes, Video Games)
www.flippers.com
"Old pinballers never die, they just flip out."

[stra...@yahoo.com]

And if it has a large value (1000-4700uF) cap inside the feedback loop that is failing, that can cause severe linearity issues.

G²

[John Robertson]

On 2017/07/05 12:35 AM, stra...@yahoo.com wrote:
> And if it has a large value (1000-4700uF) cap inside the feedback loop that is failing, that can cause severe linearity issues.
>
> G²
>

Granted, however the OP did say he recapped the monitor and I didn't
want to doubt his statement.

[mhoo...@gmail.com]

its an IC, an LA7833( nte1773) . i'll change it out and see what happens. i did change out every cap, and it was exactly the same. no better, no worse.

thanks much

[mhoo...@gmail.com]

just got done replacing the vertical IC, la7833. no change in the image. no better, no worse.

[John Robertson]

Any schematic you can provide a link to? Someone suggested a bad yoke,
which is possible if the bottom half of the vertical deflection shorted
out. Maybe. However a schematic would help.

[rickman]

Looks like the 24 volt supply is generated by doubling the 12 volt supply.
Measure the 24 volt supply at pin 6. I bet something is wrong that this is
only 12 volts, maybe the diode?

--

Rick C

[mhoo...@gmail.com]

https://na.suzohapp.com/pdf/service_pdfs/support/visionpro/49-1329-vp2_manual.pdf

https://na.suzohapp.com/pdf/service_pdfs/support/visionpro/49-1329-vp2_schematic.pdf

B+ is 12v3, 12V and 24V good. i was thinking yoke, but they ohm out good, and look like brand new. no physical damage. looks like a few transistors are after the vertical ic, i'm looking at them now. not real good at following this schematic, so any help is appreciated.

thanks

[rickman]

I'm not so good at following this schematic myself. It looks like W402 is
the connector to the yoke. If so, I would say Q404 sets the vertical
position. Q360 and D307 link the vertical drive signal to I201, the color
gun controller. Perhaps this is creating too large a load from a bad part,
so the drive is clipped?

Did you say I302 pin 2 has a square wave on it? Shouldn't that be a sawtooth?

--

Rick C

[Jeroni Paul]

mhoo...@gmail.com wrote:
> https://na.suzohapp.com/pdf/service_pdfs/support/visionpro/49-1329-vp2_manual.pdf
>
> https://na.suzohapp.com/pdf/service_pdfs/support/visionpro/49-1329-vp2_schematic.pdf
>
> B+ is 12v3, 12V and 24V good. i was thinking yoke, but they ohm out good, and look like brand new. no physical damage. looks like a few transistors are after the vertical ic, i'm looking at them now. not real good at following this schematic, so any help is appreciated.
>
> thanks

In the yoke there are two coils for vertical and two for horizontal connected in series or parallel depending on the design, if in parallel one coil connection could be broken. The coils are connected together in the solder posts on the yoke, you may check there if some wire looks loose.

[mhoo...@gmail.com]

thats a great idea, i didnt know the coils were doubled up. i will check that for sure tonite. i was thinking of inverting the image, there are solder pads for an inverted header on the chassis board, and see what the image does. that would tell me if its the yoke or a chassis issue. does that make sense?

thanks much

[John-Del]

Not saying the yoke is the problem, but a single turn shorted to an adjacent turn will not change the resistance reading on your dmm, but a single shorted turn will totally collapse the magnetic field of the coil.

A ringer is the best instrument to check for shorted turns.

[mhoo...@gmail.com]

not sure what a ringer is, but im pretty sure i dont have one. you mean like a tone generator, and you move it around the yoke ?

[Ian Field]

"John Robertson" <sp...@flippers.com> wrote in message
news:9vOdneJtZoCTHsHE...@giganews.com...

> On 2017/07/04 5:44 PM, mhoo...@gmail.com wrote:
>> ive got a tovis mtg-1901cn cga color monitor. in use, or with a test
>> pattern, the image starts out perfectly at the top. as you move down
>> toward the middle , it gradually starts to compress the image, with more
>> compression the closed you get to center. and when it gets to mid
>> screen, its a full vertical collapse. bright while line across the
>> center, with no image whatsoever in the lower 50% of the screen. also
>> sold as a vision pro .
>>
>> battery voltage is good at 123, 12v and 24 v are good. 123 volts at the
>> flyback.
>> the vertical output ic is a LA7833. pin 6 has good 24 volt supply, and
>> pin 2 ( output) is a nice 24 v square wave. i recapped the monitor,
>> and the image is exactly the same. now im stuck.
>>
>> thanks
>>
>
> Your vertical circuit is missing the bottom deflection half of the
> vertical circuit. If the vertical driver is an IC, replace it, if it is a
> pair of transistors then I would suspect the transistor pulling to ground
> (typically the lower of the two on schematics) is the one at fault.
>
> The vertical drive is just a very slow audio amp, apply audio amp service
> methods.

Not quite - it has flyback boost and tailored feedback for linearity.

Either of those can cause similar symptoms.

[Ian Field]

<mhoo...@gmail.com> wrote in message
news:c5b3309f-f414-4936...@googlegroups.com...

There might be a flyback diode lurking nearby - it could've gone leaky.

[Ian Field]

"John-Del" <ohg...@gmail.com> wrote in message
news:514af99a-2f1b-41a7...@googlegroups.com...

DSE did one, but I don't think the kit is available anymore.

The schematic is floating about and there's no unobtanium in the parts list.

[John-Del]

A dedicated instrument that checks inductors for shorted turns by injecting a waveform and counting the "rings" (like echos). A shorted coil won't ring or will ring very low. In the old days, several companies made "flyback" testers that would check flybacks and yokes for shorted turns. I have a Sencore LC75 that has a ringing feature and it works well.

Another way of checking the yoke out of the circuit can be done with a scope. If you can identify and electrically separate the two halves of the vertical yoke, you can connect each section to the calibration output jack of your scope and monitor the resulting waveform of each. Unless the top section shorted to the bottom, you can be pretty confident you have one good section and one bad. If the waveform on one of the sections is severely distorted compared to the other, it's a yoke issue. If both waveforms look the same, the yoke is most likely good.

[John Robertson]

The old DS ringer was designed by Bob Parker and was best for checking
flybacks (LOPTs), not much use on yokes I'm afraid. The kit is now made
by Anatek (we carry it on Flippers), but you would be better off with an
inductance meter - split the vertical windings and each side should be
identical.

[John Robertson]

On 2017/07/06 2:22 PM, Ian Field wrote:
>
>
> <mhoo...@gmail.com> wrote in message
> news:c5b3309f-f414-4936...@googlegroups.com...
>> On Wednesday, July 5, 2017 at 9:34:41 AM UTC-4, mhoo...@gmail.com wrote:
>>> On Wednesday, July 5, 2017 at 3:39:44 AM UTC-4, John Robertson wrote:
>>> > On 2017/07/05 12:35 AM, stra...@yahoo.com wrote:
>>> > > And if it has a large value (1000-4700uF) cap inside the feedback
>>> > > loop that is failing, that can cause severe linearity issues.
>>> > >
>>> > > G²
>>> > >
>>> >
>>> > Granted, however the OP did say he recapped the monitor and I didn't
>>> > want to doubt his statement.
>>> >
>>> > John ;-#)#
>>>

>>> its an IC, an LA7833( nte1773) . i'll change it out and see what
>>> happens. i did change out every cap, and it was exactly the same. no
>>> better, no worse.
>>>
>>> thanks much
>>
>> just got done replacing the vertical IC, la7833. no change in the
>> image. no better, no worse.
>
> There might be a flyback diode lurking nearby - it could've gone leaky.

Flyback diode won't affect the vertical deflection. You will lose the
HOT though if that diode is open. Nowadays they are part of the HOT though.

[rickman]

I don't get why your idea is not good. If you can flip the drive signal
polarity the image will invert. If the problem is in the drive circuitry
the half that is working will swap with the half that loses drive. If the
problem is in the yoke the image will invert, but the problem won't. No
need for fancy testers or widgets. Or maybe there is something I don't
understand about this?

--

Rick C

[John Robertson]

Great point Rick, that would indeed be a good test to see if the yoke is
linear or not.

[mhoo...@gmail.com]

i soldered a header into the reverse position on the chassis, and gave it a try. it did the same thing as before, just inverted. now the bottom half of the screen has an image that compresses toward the center, a total collapse on the center, and no image in the upper half of the screen. does that rule out a yoke problem?

thanks

[John Robertson]

> i soldered a header into the reverse position on the chassis, and gave it a try. it did the same thing as before, just inverted. now the bottom half of the screen has an image that compresses toward the center, a total collapse on the center, and no image in the upper half of the screen. does that rule out a yoke problem?
>
> thanks
>

Based on Rick's points above I think we can rule out the yoke. Nice work
Rick and yourself for that test!

If you have a 'scope then now is a good time to check the outputs of the
LA7851's sawtooth wave generator. Also 'scope the output of the vertical
drive IC to is if it too is still a saw tooth or not. Should swing
pretty much the entire source voltage (24VDC?) if I am not mistaken...

[John-Del]

On Tuesday, July 4, 2017 at 8:44:59 PM UTC-4, mhoo...@gmail.com wrote:

I didn't read back through all the posts, but if you haven't, check the pump up diode. The anode will be connected to the Vcc and the cathode to the pump up pin of the vert IC. A weak diode here will cause all sorts of havoc (don't check it with a dmm - they often sag under load). Also, I know you said you recapped the monitor, but make sure the yoke coupling capacitor was included. This is typically a high value capacitor (around 1000uf or more).

[mhoo...@gmail.com]

i may have hit the wall here. pin 14 of the LA7851 is a nice 5v sawtooth. pin 15 is a 12v volts square wave. pin 16 is kind of an ugly bowl shape waveform. pin 17 has nothing. on the la7833 pin 4, which i believe is the input, has the same ugly bowl shape wave, where i think it ought to have a saw tooth? pin two, the output has a very nice 24V square, which i dont think it should have. should be a 24v sawtooth? odd that it puts out a very defined square, instead of just some ugly shape, if something is wrong. i think the pump up is ok, as the output is 24v, but maybe im wrong. im thinking of just replacing the 7851 as a hail mary, and then bailing if that doesnt work.

[rickman]

This would be a lot easier if you had a working unit to compare waveforms.
It doesn't make sense to me that pin 15 if the LA7851 would be a square
wave. I think I'd try to find something wrong with the parts between pins
15 and 16. Or maybe the components from the LA7833 pin 2 to pin 17 on the
LA7851. I'm guessing this latter circuit is for linearization of the ramp
and might cause the problem you see if a part is bad. It's a bit hard to
figure out what all this does. Looks like the whole thing is pretty highly
optimized.

Are the signals on pin 2 and pin 15 of the two parts the same polarity or
opposite? I can't see how you would get a bowl shape signal on pin 16 if
they are the same. Have you played with the vertical size and linearity
controls to see how they affect the problem?

The charge pump circuit was bothering me as the diode seemed to be
backwards. Then I realized it isn't making 24 volts from 12 volts, it's
pumping up the 24 volts to something higher! What is the voltage on pin 3
of the LA7833? The cap is only rated for 35 volts, so it isn't making 48
volts. But clearly pin 3 should have something on it higher than 24 volts.
What does the pump drive signal on pin 7 look like?

--

Rick C

[mhoo...@gmail.com]

pin 3 of 7833 is 25.65 v. pins 2 and 15 are opposite polarity. pump drive signal is a .5 volts upside down sawtooth.

i appreciate the time taken here. i could just send this out, but i think i am close, just not there.

[jurb...@gmail.com]

Ramp generator, probably at whatever that unit's equivalent of a jungle IC is. An IC is only as good as what is fed into it. Yoke problems are rare and thus unlikely.

You need a proper sawtooth wave driving that IC or it will not put out what you want. It is that simple. So go backwards and find that ramp generator. If you cannot find it, put up a link to the print and I will. If you do, please use something that an older PC can use.

[rickman]

If pin 7 pump drive signal is only half a volt, I would say your problem is
there. Pin 3 should clearly be more than 25 volts and it is this signal
that drives that voltage. Is pin 3 at all steady or is it also a waveform?
You should measure the voltage with the scope, not the meter. They don't
use a smoothing cap so I guess the voltage will pulse with the drive.
During retrace you don't need a high voltage on pin 3. Retrace is when the
voltage goes below 24 volts and the diode is forward biased to charge up the
cap again.

I think you said you already replaced the LA7833, so there are only two
other parts. When you say pin 7 is "upside down", do you mean it is
normally high and drops low or it is going negative? I would expect it to
be near 24 volts during the picture time and drops low during retrace as the
cap charges. I guess the question is how does the waveform on pin 3 look?
I would expect it mostly near 48 volts dropping slightly below 24 volts
during retrace. Pin 7 should definitely have a significant pulse voltage on
it.

--

Rick C

[John Robertson]

On 2017/07/07 10:01 AM, mhoo...@gmail.com wrote:
> On Friday, July 7, 2017 at 12:09:33 PM UTC-4, rickman wrote:
>> mhoo...@gmail.com wrote on 7/7/2017 10:55 AM:
>>> On Friday, July 7, 2017 at 9:52:26 AM UTC-4, John-Del wrote:
>>>> On Tuesday, July 4, 2017 at 8:44:59 PM UTC-4, mhoo...@gmail.com wrote:
>>>>> ive got a tovis mtg-1901cn cga color monitor. in use, or with a test pattern, the image starts out perfectly at the top. as you move down toward the middle , it gradually starts to compress the image, with more compression the closed you get to center. and when it gets to mid screen, its a full vertical collapse. bright while line across the center, with no image whatsoever in the lower 50% of the screen. also sold as a vision pro .
>>>>>
>>>>> battery voltage is good at 123, 12v and 24 v are good. 123 volts at the flyback.
>>>>> the vertical output ic is a LA7833. pin 6 has good 24 volt supply, and pin 2 ( output) is a nice 24 v square wave. i recapped the monitor, and the image is exactly the same. now im stuck.
>>>>>
>>>>> thanks
>>>>
>>>> I didn't read back through all the posts, but if you haven't, check the pump up diode. The anode will be connected to the Vcc and the cathode to the pump up pin of the vert IC. A weak diode here will cause all sorts of havoc (don't check it with a dmm - they often sag under load). Also, I know you said you recapped the monitor, but make sure the yoke coupling capacitor was included. This is typically a high value capacitor (around 1000uf or more).
>>>
>>> i may have hit the wall here. pin 14 of the LA7851 is a nice 5v sawtooth. pin 15 is a 12v volts square wave. pin 16 is kind of an ugly bowl shape waveform. pin 17 has nothing. on the la7833 pin 4, which i believe is the input, has the same ugly bowl shape wave, where i think it ought to have a saw tooth? pin two, the output has a very nice 24V square, which i dont think it should have. should be a 24v sawtooth? odd that it puts out a very defined square, instead of just some ugly shape, if something is wrong. i think the pump up is ok, as the output is 24v, but maybe im wrong. im thinking of just replacing the 7851 as a hail mary, and then bailing if that doesnt work.
>>

>> This would be a lot easier if you had a working unit to compare waveforms..

>> It doesn't make sense to me that pin 15 if the LA7851 would be a square
>> wave. I think I'd try to find something wrong with the parts between pins
>> 15 and 16. Or maybe the components from the LA7833 pin 2 to pin 17 on the
>> LA7851. I'm guessing this latter circuit is for linearization of the ramp
>> and might cause the problem you see if a part is bad. It's a bit hard to
>> figure out what all this does. Looks like the whole thing is pretty highly
>> optimized.
>>
>> Are the signals on pin 2 and pin 15 of the two parts the same polarity or
>> opposite? I can't see how you would get a bowl shape signal on pin 16 if
>> they are the same. Have you played with the vertical size and linearity
>> controls to see how they affect the problem?
>>
>> The charge pump circuit was bothering me as the diode seemed to be
>> backwards. Then I realized it isn't making 24 volts from 12 volts, it's
>> pumping up the 24 volts to something higher! What is the voltage on pin 3
>> of the LA7833? The cap is only rated for 35 volts, so it isn't making 48
>> volts. But clearly pin 3 should have something on it higher than 24 volts.
>> What does the pump drive signal on pin 7 look like?
>>
>> --
>>
>> Rick C
>
> pin 3 of 7833 is 25.65 v. pins 2 and 15 are opposite polarity. pump drive signal is a .5 volts upside down sawtooth.
>
> i appreciate the time taken here. i could just send this out, but i think i am close, just not there.
>

Afraid we don't have one on the service bench otherwise I would be happy
to send you waveform images. One of those monitors is in my storage area
I'm pretty sure, but...


John :-#(#

[Ian Field]

"John Robertson" <sp...@flippers.com> wrote in message

news:3rudnUQ-koXXLMPE...@giganews.com...

I tried the DSE ringer on pretty much anything laying around - it doesn't
like very low inductances.

Scan yokes should be fine.

[Ian Field]

"John Robertson" <sp...@flippers.com> wrote in message

news:3rudnUc-koUQLMPE...@giganews.com...

> On 2017/07/06 2:22 PM, Ian Field wrote:
>>
>>
>> <mhoo...@gmail.com> wrote in message
>> news:c5b3309f-f414-4936...@googlegroups.com...
>>> On Wednesday, July 5, 2017 at 9:34:41 AM UTC-4, mhoo...@gmail.com wrote:
>>>> On Wednesday, July 5, 2017 at 3:39:44 AM UTC-4, John Robertson wrote:
>>>> > On 2017/07/05 12:35 AM, stra...@yahoo.com wrote:
>>>> > > And if it has a large value (1000-4700uF) cap inside the feedback
>>>> > > loop that is failing, that can cause severe linearity issues.
>>>> > >
>>>> > > G²
>>>> > >
>>>> >
>>>> > Granted, however the OP did say he recapped the monitor and I didn't
>>>> > want to doubt his statement.
>>>> >
>>>> > John ;-#)#
>>>>
>>>> its an IC, an LA7833( nte1773) . i'll change it out and see what
>>>> happens. i did change out every cap, and it was exactly the same. no
>>>> better, no worse.
>>>>
>>>> thanks much
>>>
>>> just got done replacing the vertical IC, la7833. no change in the image.
>>> no better, no worse.
>>
>> There might be a flyback diode lurking nearby - it could've gone leaky.
>
> Flyback diode won't affect the vertical deflection. You will lose the HOT
> though if that diode is open. Nowadays they are part of the HOT though.

The one in the vertical output section can and does.

[Ian Field]

"John Robertson" <sp...@flippers.com> wrote in message

news:ComdnW2tcfL-SMLE...@giganews.com...

Pretty sure you can wire up an adaptor to run VGA off a CGA output - for
some strange reason, many VGA monitors aren't backward compatible with EGA.

[John Robertson]

There are CGA -> VGA adapters on eBay all the time. Cheap. Most work,
some don't so do some research first.

John :-#)#

[mhoo...@gmail.com]

On Friday, July 7, 2017 at 1:24:17 PM UTC-4, jurb...@gmail.com wrote:
> Ramp generator, probably at whatever that unit's equivalent of a jungle IC is. An IC is only as good as what is fed into it. Yoke problems are rare and thus unlikely.
>
> You need a proper sawtooth wave driving that IC or it will not put out what you want. It is that simple. So go backwards and find that ramp generator. If you cannot find it, put up a link to the print and I will. If you do, please use something that an older PC can use.

https://na.suzohapp.com/pdf/service_pdfs/support/visionpro/49-1329-vp2_schematic.pdf

[Dimitrij Klingbeil]

Did you check D360 (the "bootstrap" diode from 24V in the pump circuit)?

It may be shorted and pulling the "pumped" supply "down" to 24V. The IC
will most likely need the pumped supply for one half of the screen only.

[Dimitrij Klingbeil]

Look up "impulse winding tester", that's the high voltage version.
Ring testers work the same way, with V rather than kV scale drive.

[mhoo...@gmail.com]

i did pull up one leg of D360 and checked it, it checked good. pin 7 never goes anywhere near 24 volt. there is a .5 volts poorly defined waveform, almost looks like ripple. im thinking it should be a 24v sawtooth? i am thinking something on the board may be pulling down pin 7?

thanks

[mhoo...@gmail.com]

just to be clear, the pin 7 is 1/2 volt(.5) ripple like form

thanks

[John-Del]

On Saturday, July 8, 2017 at 9:58:10 PM UTC-4, mhoo...@gmail.com wrote:

You can't check this diode with a dmm... I posted above:

[Ian Field]

<mhoo...@gmail.com> wrote in message
news:ce6b58ea-d6d6-4fa0...@googlegroups.com...

> On Thursday, July 6, 2017 at 3:58:22 PM UTC-4, John-Del wrote:

>> On Thursday, July 6, 2017 at 11:18:38 AM UTC-4, mhoo...@gmail.com wrote:

>> > On Thursday, July 6, 2017 at 7:17:12 AM UTC-4, rickman wrote:

>> > > mhoo...@gmail.com wrote on 7/6/2017 1:00 AM:
>> > > > On Wednesday, July 5, 2017 at 9:34:41 AM UTC-4, mhoo...@gmail.com
>> > > > wrote:
>> > > >> On Wednesday, July 5, 2017 at 3:39:44 AM UTC-4, John Robertson
>> > > >> wrote:
>> > > >>> On 2017/07/05 12:35 AM, stra...@yahoo.com wrote:
>> > > >>>> And if it has a large value (1000-4700uF) cap inside the
>> > > >>>> feedback loop that is failing, that can cause severe linearity
>> > > >>>> issues.
>> > > >>>>
>> > > >>>> G²
>> > > >>>>
>> > > >>>
>> > > >>> Granted, however the OP did say he recapped the monitor and I
>> > > >>> didn't
>> > > >>> want to doubt his statement.
>> > > >>>

>> > > >>> John ;-#)#
>> > > >>>
>> > > >>> --
>> > > >>> (Please post followups or tech inquiries to the USENET newsgroup)
>> > > >>> John's Jukes Ltd.
>> > > >>> MOVED to #7 - 3979 Marine Way, Burnaby, BC, Canada V5J 5E3
>> > > >>> (604)872-5757 (Pinballs, Jukes, Video Games)
>> > > >>> www.flippers.com
>> > > >>> "Old pinballers never die, they just flip out."
>> > > >>

>> > > >> its an IC, an LA7833( nte1773) . i'll change it out and see what
>> > > >> happens. i did change out every cap, and it was exactly the same.
>> > > >> no better, no worse.
>> > > >>
>> > > >> thanks much
>> > > >
>> > > > just got done replacing the vertical IC, la7833. no change in the
>> > > > image. no better, no worse.
>> > >

>> > > Looks like the 24 volt supply is generated by doubling the 12 volt
>> > > supply.
>> > > Measure the 24 volt supply at pin 6. I bet something is wrong that
>> > > this is
>> > > only 12 volts, maybe the diode?
>> > >
>> > > --
>> > >
>> > > Rick C
>> >
>> >
>> > https://na.suzohapp.com/pdf/service_pdfs/support/visionpro/49-1329-vp2_manual.pdf
>> >
>> > https://na.suzohapp.com/pdf/service_pdfs/support/visionpro/49-1329-vp2_schematic.pdf
>> >
>> > B+ is 12v3, 12V and 24V good. i was thinking yoke, but they ohm out
>> > good, and look like brand new. no physical damage.
>>
>> Not saying the yoke is the problem, but a single turn shorted to an
>> adjacent turn will not change the resistance reading on your dmm, but a
>> single shorted turn will totally collapse the magnetic field of the coil.
>>

>> A ringer is the best instrument to check for shorted turns.
>
> not sure what a ringer is, but im pretty sure i dont have one. you mean
> like a tone generator, and you move it around the yoke ?

The DSE one has a comparator rigged to generate spike pulses - the ringing
pulses clock a logic 1 along a shift register and basically counts how many
times the inductor rings.

The schematic is floating about the web, and there's nothing hard to find in
the parts list.

[Foxs Mercantile]

On 7/9/2017 1:13 PM, Ian Field wrote:
> The DSE one has a comparator rigged to generate spike pulses -
> the ringing pulses clock a logic 1 along a shift register and
> basically counts how many times the inductor rings.
>
> The schematic is floating about the web, and there's nothing
> hard to find in the parts list.

<https://www.flippers.com/fbt-main.html>



--
Jeff-1.0
wa6fwi
http://www.foxsmercantile.com

---
This email has been checked for viruses by AVG.
http://www.avg.com

[mhoo...@gmail.com]

i swapped the D360 diode with another from the board, no difference. i dont really understand from the schematic what the pump up circuit is. it has 24V thru a electrolytic cap in series to pin7 . is that an input or an output? the same circuit( before the cap) goes to pin 3. there is only about 1/2 volt on pin 7. is it supposed to pulse, pin 7 pulling down the 24 v?

[John Robertson]

>>> will most likely need the pumped supply for one half of the screen only..

>>
>> i did pull up one leg of D360 and checked it, it checked good. pin 7 never goes anywhere near 24 volt. there is a .5 volts poorly defined waveform, almost looks like ripple. im thinking it should be a 24v sawtooth? i am thinking something on the board may be pulling down pin 7?
>>
>> thanks
>
> You can't check this diode with a dmm... I posted above:
>
>
> "I didn't read back through all the posts, but if you haven't, check the pump up diode. The anode will be connected to the Vcc and the cathode to the pump up pin of the vert IC. A weak diode here will cause all sorts of havoc (don't check it with a dmm - they often sag under load)."
>

That is a most interesting point, the 1N4937 diode is indeed a fast
switching diode and it certainly appears to be critical for building the
vertical deflection. Your point about sagging under load could indeed be
correct for this problem as described by the OP.

Learn something every day, thanks!

John :-#)#

[Ian Field]

<mhoo...@gmail.com> wrote in message
news:5dc0ef0f-2541-446c...@googlegroups.com...

There's sometimes an electro with ambiguous purpose (also on audio amps). It
bootstraps the output to the bias network for the output transistor bases.
Its almost positive feedback that reduces drive current requirement for the
output pair and improves linearity.

[mhoo...@gmail.com]

just replaced the vertical deflection IC LA7851. same image, no better. regarding d360 possibly sagging, i did swap it with another on the board, and it was the same. i'll have to keep digging, but any help is appreciated.

thanks

[John-Del]

On Monday, July 10, 2017 at 7:22:44 PM UTC-4, mhoo...@gmail.com wrote:

> just replaced the vertical deflection IC LA7851. same image, no better. regarding d360 possibly sagging, i did swap it with another on the board, and it was the same. i'll have to keep digging, but any help is appreciated.
>
> thanks

Not much left...

Try warming up the board with a hair dryer on high or a heat gun on low and watch the picture as you do. I'd bet dollars to donuts at this point that the picture stretches out. You said you recapped the monitor but was this all the larger electros that are known to cause issues (like a kit) or *everything*. There are often low value electrolytics back at the signal generator side used for signal coupling that get juicy on the bottom and cause issue either from low esr (they can be juicy and still check OK) or from conductive contamination from the leaked electrolyte.

If the heat doesn't expose a lazy high esr coupling cap, then try washing the board with a suitable cleaner and acid brush, removing the "jungle" IC if need be but otherwise clean between all the leads.

[mhoo...@gmail.com]

well, im starting to think that its going into HV shutdown, and rather than shutting down, the half scan is how it was made to shutdown. still, doesnt shutdown usually not shut down the vertical scan ? i dont think anything on this unit is the usual. the manual for it is near useless, very little info. another thing, the schematic shows two pairs of jumpers, for 13 or 19 inch use. both pairs are jumped on this board, and the same board on ebay has both pairs jumped. its a hair puller. pin 13 on the 7851 is the x ray protection pin, and it needs to be a specific voltage or the chip shuts down. the manual says that, but doesnt say the voltage. im going to end up buying a chasssi, but i'd still like to know what the heck is wrong with mine.

thanks

[John-Del]

When projection TVs started hitting the market, manufacturers soon learned that a scan loss in either direction would immediately destroy the CRTs. In response, manufacturers learned to not start the HV until both deflections were established, and shut down same if one was lost or even diminished by a fixed percent. The point is that a vertical collapse would not be the result of a shutdown, but a cause.

Read my previous post again. One of the last CRT TVs I worked on was a Zenith 35" console with a stubborn vert (slow to fill, weird linearity issues). It turned out that the board became conductive from leaked electrolyte and dust. Heating and cooling the board affected the deflection, but no components were themselves temperature sensitive. I ended up pulling the flyback, smps transformer, and any inductor that looked like it could hold water and immersed the whole board in a parts cleaner. Once assembled, the vertical was perfect and didn't drift.

[mhoo...@gmail.com]

this board is so clean you could eat off of it. im also looking into that it may be lacking the pulse feed from the flyback to the vert ic.

[rickman]

If the high voltage section shuts down you would lose the brightness of the
electron beam, no? Sounds from your description the electron beam is
clearly visible when the deflection collapses.

--

Rick C

[mhoo...@gmail.com]

i put a probe on pin 4 of LA7851, the vertical deflector ic chip. its a pulse from the AFC terminal on the flyback. there is virtually no pulse, just a half volt . from the flyback afc terminal, i get a 90 volt shape that looks like a half rectified sine wave, just the top of the sine wave. 90 volt seems low. i think there has to be a pulse at pin 4 for the IC to operate. i bought a working chassis on ebay, and will check some pins outputs, i dont want to give up now.

[Ian Field]

<mhoo...@gmail.com> wrote in message
news:623898bb-74ce-45f0...@googlegroups.com...

The number sounds familiar - but its been a while.

some vertical chips were just the power stage while others included the ramp
generator etc. If it does and you've tried replacement, you might need to
consider what was said about shorted turns on the yoke.

Some of the passives can cause trouble, but they're easier to test than
shorted turns.

[Ian Field]

"John Robertson" <sp...@flippers.com> wrote in message

news:K8SdnaFrHtPRKv7E...@giganews.com...

Its a fairly common type number - I've certainly encountered *MUCH* less
reliable diodes along the way.

Not that I've never had to replace one, but they're not prominent in the
stock faults list.

[John Robertson]

It that is a working chassis for that board it would be great if you can
photograph the 'scope images and post them somewhere. I can capture them
and add to flippers library of tech tips for folks to use in the future...

[John Robertson]

Oddly enough I've had to replace every 1N4002 diode used in one home
pinball game from the 1970s (Fischer's Sky Hawk) because they fail at
random. They appeared to be the world's cheapest diode - early Chinese?
- the body isn't a smooth cylinder rather it is lumpy.

I have to agree that diodes in monitors rarely fail, I can't recall the
last time we traced a problem to a faulty diode.

Now pinball power supplies? Those we replace diodes from time to time...

[Ralph Mowery]

In article <1ridnZ11qfjO4fvE...@giganews.com>,
sp...@flippers.com says...

>
>

> Oddly enough I've had to replace every 1N4002 diode used in one home
> pinball game from the 1970s (Fischer's Sky Hawk) because they fail at
> random. They appeared to be the world's cheapest diode - early Chinese?
> - the body isn't a smooth cylinder rather it is lumpy.
>
> I have to agree that diodes in monitors rarely fail, I can't recall the
> last time we traced a problem to a faulty diode.
>
>

I never did understand why they make a series of diodes like the 1n4001
to 1n4007, each with a higher voltage rating. My only thought is they
make a batch like the microprocessors and test each one to see its
maximum rating and mark the lesser ones at a slightly lower price. I do
think the 1n4007 may be a slightly different kind of makeup than the
others. Another thing is odd voltage cpacitors like a 63 volt unit.
Why not just 60 or 70 or even 65 due to the large tollorance of them.

[Ian Field]

"John Robertson" <sp...@flippers.com> wrote in message

news:1ridnZ11qfjO4fvE...@giganews.com...

There was a European BA prefix family of diodes that I can't remember the
numerical bit that were seriously dodgy.

There was a block package E/W diode that could be single or double and had
an SK prefix (IIRC) that I routinely replaced whether they'd failed or not.

Not many in monitors - nearly all in TVs.

[Ian Field]

"Ralph Mowery" <rmower...@earthlink.net> wrote in message
news:MPG.33d059d02...@news.east.earthlink.net...

Last time I ordered diodes - all the PIV grades were the same price, I just
ordered the highest grade in a larger quantity.

I have absolutely no idea how they grade production and marketing.

[mhoo...@gmail.com]

well, i got the new chassis and its working correctly. turns out my chassis i recapped and went all sorts of nuts on is most likely good. it was the control board with size, horz, vertical, contrast and the other adjustments. it plugs in via a ribbon cable. if i use my old control board with the new chassis, i get the same half image. i never thought control board, as i got the half image with the board connected and unconnected, and mvoing the pots made no difference. i have both boards and will go over the pots, resistors, 1 diode and 1 cap. see whats bad on the affected board, maybe the cable itself. its soldered, not crimped. i cant really test my old chassis, i had to use my old neck board, it was for a 13, not 19 inch monitor. not going to swap neck boards back and forth, im just glad its working. i will let all know if i find the control board issue

[John Robertson]

Thanks for the update! I had forgotten about the sub-board controller
too, and we have run into that with other monitors.

I suspect now that one of the vertical potentiometers is damaged.....

[mhoo...@gmail.com]

the vert pot is open. schematic shows a 500ohm B pot. what is the b for. two of the pots have the b suffix. google had conflicting info that its a log pot, but testing the good one with a dvm, it looks linear( i need a battery for my analog meter) . thanks

[John Robertson]

On 2017/07/15 9:25 AM, mhoo...@gmail.com wrote:
> On Friday, July 14, 2017 at 7:19:32 PM UTC-4, John Robertson wrote:
>> On 2017/07/14 4:03 PM, mhoo...@gmail.com wrote:
>>> On Thursday, July 13, 2017 at 4:03:55 PM UTC-4, Ian Field wrote:
>>>> "Ralph Mowery" <rmower...@earthlink.net> wrote in message
>>>> news:MPG.33d059d02...@news.east.earthlink.net...
>>>>> In article <1ridnZ11qfjO4fvE...@giganews.com>,
>>>>> sp...@flippers.com says...
>>>>>>
>>>>>>
>>>>>
>>>>>> Oddly enough I've had to replace every 1N4002 diode used in one home
>>>>>> pinball game from the 1970s (Fischer's Sky Hawk) because they fail at
>>>>>> random. They appeared to be the world's cheapest diode - early Chinese?
>>>>>> - the body isn't a smooth cylinder rather it is lumpy.
>>>>>>
>>>>>> I have to agree that diodes in monitors rarely fail, I can't recall the
>>>>>> last time we traced a problem to a faulty diode.
>>>>>>
>>>>>>
>>>>> I never did understand why they make a series of diodes like the 1n4001
>>>>> to 1n4007, each with a higher voltage rating. My only thought is they
>>>>> make a batch like the microprocessors and test each one to see its
>>>>> maximum rating and mark the lesser ones at a slightly lower price. I do
>>>>> think the 1n4007 may be a slightly different kind of makeup than the
>>>>> others. Another thing is odd voltage cpacitors like a 63 volt unit.
>>>>> Why not just 60 or 70 or even 65 due to the large tollorance of them.
>>>>
>>>> Last time I ordered diodes - all the PIV grades were the same price, I just
>>>> ordered the highest grade in a larger quantity.
>>>>
>>>> I have absolutely no idea how they grade production and marketing.
>>>

>>> well, i got the new chassis and its working correctly. turns out my chassis i recapped and went all sorts of nuts on is most likely good. it was the control board with size, horz, vertical, contrast and the other adjustments. it plugs in via a ribbon cable. if i use my old control board with the new chassis, i get the same half image. i never thought control board, as i got the half image with the board connected and unconnected, and mvoing the pots made no difference. i have both boards and will go over the pots, resistors, 1 diode and 1 cap. see whats bad on the affected board, maybe the cable itself. its soldered, not crimped. i cant really test my old chassis, i had to use my old neck board, it was for a 13, not 19 inch monitor.. not going to swap neck boards back and forth, im just glad its working. i will let all know if i find the control board issue

>>>
>>
>> Thanks for the update! I had forgotten about the sub-board controller
>> too, and we have run into that with other monitors.
>>
>> I suspect now that one of the vertical potentiometers is damaged.....
>>
>> John :-#)#
>>

> the vert pot is open. schematic shows a 500ohm B pot. what is the b for. two of the pots have the b suffix. google had conflicting info that its a log pot, but testing the good one with a dvm, it looks linear( i need a battery for my analog meter) . thanks
>

Cute, will try to remember damaged pots for the future. Always look for
the simple stuff first - usually my rule, but hey, who expects broken pots?

And, of course, I should.

John :-#(#

[Ian Field]

"John Robertson" <sp...@flippers.com> wrote in message

news:1sSdnRg-g4_B0vfE...@giganews.com...

Pots became extinct just before CRTs. Now all the settings are on EEPROM.

[Chuck]

On Sat, 15 Jul 2017 10:22:36 -0700, John Robertson <sp...@flippers.com>
wrote:

Another vertical pot problem I have seen is leakage between the
potentiometer and a grounded case.

---
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[Ian Field]

"Chuck" <c...@dejanews.net> wrote in message
news:qpskmcdlop3fnpjg5...@4ax.com...

The one I've seen most of is loose rotor and flaky contact between wiper and
track.