CPD1604S Vertical Collapse

[vol.2]

So I got this Sony PC monitor from 1992 that didn't work when I picked it up. I went ahead and tested all the caps and replaced anything bad. There was a absolute ton of caps that had gone high ESR (we are talking 300kOhms high) and there is one board in particular, the DA board, that used surface mount caps which had leaked all over the place.

On the DA board, I removed all the caps and clean it thoroughly with white vinegar and let it sit until it stopped foaming. I cleaned that off and then soaked it with 99% IPA and dried it off with compressed air and let it sit for days to make sure it was dry. The DA board is almost all surface mount, and there are no transformers or anything that might get messed up by being wet. I sprayed all the pots with deoxit and fiddled them a bit to make sure they didn't harbor salts or crust from the whole process.

I also inspected the DA board under a microscope and tested continuity on any areas that seemed more corroded. There didn't appear to be any such issues, and the traces didn't seem to be broken, only exposed in some areas. I suppose it's possible that something under an IC is bad, or a via got damaged because it's a multi-layered board with components on the back side. There is absolutely no apparent damage to the back side.

When I got everything back together, I turned on and I got HV, but the image was vertically collapsed. It's only a few pixels high, but it's there enough that I can actually make out the colors in the line and it reflects what should be seen on the screen. For example, I can see where the Windows logo starts and stops on boot, and I can see the proper colors change on the raster horizontally (for example a SMPTE bar image will reflect the bars color across the screen). I can also successfully shift the image horizontally with the screen controls.

My first thought was that the bad caps on the D board might have blown the Vertical Output IC before I got it, as I have run into that issue a number of times. I bought a handful of the ICs pretty cheaply, but replacing it didn't help or apparently change anything. I thought maybe the replacement could be bad, but a thorough check of the original IC revealed no shorts on the IC, and diode tests between pins seem to make sense for a working IC. I don't believe the original IC was bad at all. I suppose it's still not impossible, but I think it's okay. Anytime this has happened to me in the past, the IC had shorts or low resistance between GND and Vcc or some other pin(s).

So I'm kind of lost here just checking random things. It's extremely difficult to test voltages on this monitor because the portion of the case that holds the CRT is extremely thin and can't be supported by it's structure alone. The only way I could get it to stand up and make adjustments on the inside was to prop it up leaning forward on a towel and balance it that way. Doing this it's not possible to access the bottom of the PCB to take readings. So I disassembled the chassis again and I'm just looking more closely at the DA board in hopes that I can find a culprit.

There are a number of small ICs on the DA board that handle all the V and H stuff, and choosing the resolution, I assume based on the frequency of the incoming signal.

Can someone help me to identify which components or areas can cause this condition?

Again this is:

-General Vertical Collapse

-There are still a couple of pixels present, enough to match what you are displaying to those few lines as the input changes

-Horizontal seems to be okay in that it spans the whole screen and it is movable with controls

-High Voltage appears to be present as I'm getting the whine and the static on the screen

-Area around the Vertical output IC on the PCB is dark from heat, but none of the component are visually burned or bad and testing a couple so far they looked perfect.

Here is a link to the three pages of the schematic on imgur. I didn't want to put them in-line as they are 11x17 size and would be too big here. If you open the image links and then view them in another tab, you can expand them to see details.

D board:
https://i.imgur.com/WPsfh6y.png

DA board:
https://i.imgur.com/cd66Twn.png

Neck board:
https://i.imgur.com/sW2mfuv.png

TIA

[vol.2]

I did some more work on this project and was able to get things balanced in such a way that I could take some readings with my scope.

What I found was that I am getting what appear to be correct waveforms on the DA board when I have a standard 31kHz VGA signal plugged into the monitor.

I tested several TPs, but specifically I was able to confirm that I'm getting both proper Vertical deflection signals in from the VGA cable, and that the Vertical Deflection signal looks exactly as the SM says it should when it leaves the DA board.

I'm not sure if this means I can rule out the DA board completely, but I am more suspecting that the Vertical Deflection just isn't spinning up at all.

I already replaced the Vert output IC, and replaced the caps around it (and every other bad cap on the board), so I don't know what to try next.

Also have checked the windings on the yoke and they seem to read what I would expect in both cases.

Any ideas?

[vol.2]

So I isolated the 24VDC rail to the Vertical output IC as the culprit and traced the issue back to a fusible resistor at the transformer. It most likely blew as a result of bad caps in the power supply that I have replaced, so it's getting Vertical deflection now.

Unfortunately, I'm still having some issues with the Geometry. I can't seem to get the Pin Amp controls to straighten the sides out.

After much tweaking around with the various controls, I think it's got to be some component in the Pin Amp section of the DA board that is wrong.

Any ideas on what to focus on?

This is the section of the schematic that contains the Pin Amp stuff, and you can see the whole thing in my first post via the imgur links.

[kf4rca]

I think you probably missed a cap in there. Caps are high fail in these. Then there's the vertical output IC also.

[vol.2]

Originally Posted by kf4rca

I think you probably missed a cap in there. Caps are high fail in these. Then there's the vertical output IC also.

Nope. Didn't miss any caps. Especially not on the DA board. It's a tiny board that was mostly surface mount caps. Took em all off and all the through hole caps as well.

As I said in my last post, the Vertical is working now, unless you think the Vertical output IC could have an effect on the Pin Amp circuit on the DA board?

I did replace the Vertical IC with an NOS part, so there could be something wrong with the new one, but I don't think it's specifically handling the East West stuff, that's on the DA board.

It's using a TEA2031A for the geometry adjustments, and when I spray the thing with cold spray it gets wiggly and it looks like it's pulling the sides in. So I'm suspecting that one. I can get it cheap so I just got one coming regardless.

Attached is the datasheet

[Alex KL-1]

Indeed it can be the IC, but you changed also the low value electros in this area?

[vol.2]

Originally Posted by Alex KL-1

Indeed it can be the IC, but you changed also the low value electros in this area?

Yes, I had to change all the low value eletros. All the surface mounts spilled their guts, and the few through hole caps were quite bad. I checked the orientation of the caps many times, I didn't make any mistakes.


I tested the Pin Amp IC:

Pin 5) correct. 20 Vpkpk square wave @ 31.15kHz

Pin 6) correct 20VDC on it

Pin 7)14VDC offset from schematic is present, but the 0.5Vp-p waveform is screwy and wrong. It looks more like a sawtooth than what the schematic shows, and it's only about 250mV, not 500

Pin 8) 3.4 V pkpk sawtooth. Very close to the 3.6V pkpk shown in the service manual.

So from this I can conclude that something is fishy around the chip or inside the chip. Pin 7 is connected to ground through a 150k resistor, but in this set, it's also connected to the rest of the circuit through a 470k resistor with a cap to ground between them. I have no idea why it's done, but I can guess that maybe it's some kind of DC restoration to bring the level of the chip up to the rest of the circuit on pin 7 or possibly to enable some of the other geometry controls in some way.

Pin 7 is connected to Pin 5 through the one resistor, and the waveform on Pin 5 looks correct, so therefore, I'd basically assume that there's either something wrong with the chip, or with one of the components going to ground between the Pins.

R376- 150k - to GND from Pin 7

C340- 0.0015 - to GND from Pin 7

R375- 470k - between Pin 7 and Pin 5

Does this result say anything to you about the circuit or the failure I'm seeing; it's like something in the circuit is bring down the 500mVpkpk parabola I'm supposed to see to ~280mV and squishing the top down into noise

I attached the expected waveforms from Pins 5,7 and 8 of the Pin Amp IC, Pin 6 is the supply is supposed to be 20 V and it is.

[Alex KL-1]

Originally Posted by vol.2

Yes, I had to change all the low value eletros. All the surface mounts spilled their guts, and the few through hole caps were quite bad. I checked the orientation of the caps many times, I didn't make any mistakes.


I tested the Pin Amp IC:

Pin 5) correct. 20 Vpkpk square wave @ 31.15kHz

Pin 6) correct 20VDC on it

Pin 7)14VDC offset from schematic is present, but the 0.5Vp-p waveform is screwy and wrong. It looks more like a sawtooth than what the schematic shows, and it's only about 250mV, not 500

Pin 8) 3.4 V pkpk sawtooth. Very close to the 3.6V pkpk shown in the service manual.

So from this I can conclude that something is fishy around the chip or inside the chip. Pin 7 is connected to ground through a 150k resistor, but in this set, it's also connected to the rest of the circuit through a 470k resistor with a cap to ground between them. I have no idea why it's done, but I can guess that maybe it's some kind of DC restoration to bring the level of the chip up to the rest of the circuit on pin 7 or possibly to enable some of the other geometry controls in some way.

Pin 7 is connected to Pin 5 through the one resistor, and the waveform on Pin 5 looks correct, so therefore, I'd basically assume that there's either something wrong with the chip, or with one of the components going to ground between the Pins.

R376- 150k - to GND from Pin 7

C340- 0.0015 - to GND from Pin 7

R375- 470k - between Pin 7 and Pin 5

Does this result say anything to you about the circuit or the failure I'm seeing; it's like something in the circuit is bring down the 500mVpkpk parabola I'm supposed to see to ~280mV and squishing the top down into noise

I attached the expected waveforms from Pins 5,7 and 8 of the Pin Amp IC, Pin 6 is the supply is supposed to be 20 V and it is.

Makes all sense. We can imagine the waveforms differing a little according with CRT variances, but certainly not a radical difference. At least with my experiences with modern TV when I repairing it (and monitors), is that the waveforms always resemble the originals when it are working well. Besides the suspicious DC voltages.

[vol.2]

Originally Posted by Alex KL-1

Makes all sense. We can imagine the waveforms differing a little according with CRT variances, but certainly not a radical difference. At least with my experiences with modern TV when I repairing it (and monitors), is that the waveforms always resemble the originals when it are working well. Besides the suspicious DC voltages.

Thanks. I went ahead and probed Pins 1 and 2 of the Pin Amp IC, and it seems like the AC component that's supposed to vary the parabola on the IC's output is not properly varying when I adjust the Pin Amp potentiometers.

I am now thinking it's most likely the fault of the IC, but also maybe it's some other component in the circuit holding the IC down at the input or output.

Does anything jump out to check?

[zeno]

Be sure the V out is getting + 24 VDC. I hate shot gunning BUT if
it has @24 V change the IC & all related 'lytic caps, ALL at once.
While things are removed do resistant tests. That will fix 95% of them.

Zeno
LFOD !

[vol.2]

Originally Posted by zeno

Be sure the V out is getting + 24 VDC. I hate shot gunning BUT if
it has @24 V change the IC & all related 'lytic caps, ALL at once.
While things are removed do resistant tests. That will fix 95% of them.

Zeno
LFOD !

Yes, it's getting 24V out of the transformer now. I also scoped Pin 6 on IC303 (East West IC) and it has the indicated 20.5V supply. In fact, all of the Pins around IC303 look hunky dory except Pin 7, which is suppose to be the parabola.

I changed all the caps on the DA board already because they were the early surface mount kind and were all dead. So unfortunately I can't do resistance tests with them out of circuit.

I've got a new East West IC coming on monday, so I'll try my luck with that and cross my fingers. Otherwise, I might have to remove the caps and start looking for an open resistor or something.

[vol.2]

I replaced IC303 and I still have the weird Side Pin issue. I've been checking resistors all over the board, pulling stuff out when I have to, but I'm still not seeing any issues.

If anyone has an idea of what would maybe cause this to narrow my search I would be grateful.

[vol.2]

So this is the output of Pin 5 on IC303. I realize now that the top of it is the key to understanding the pincushion adjustment output. If you look at the top of the waveform, it's supposed to have a flat top that extends past the edges of the square wave evenly on both sides.

This waveform is incorrect as it has the top portion skewed all the way to the left. The waveform wiggles around in a manner that perfectly reflects when I tweak the Pincushion pots, and it snaps back to the left as the sides of the raster similarly refuse to be corrected.



Now I can see why it's displaying incorrectly, but I don't know why or where the problem lies. I've already spent a long time checking voltages, and nothing really seems wrong so far. I've more or less confirmed the values of all resistors, and I checked the ICs that control the mode selection.

Where should I focus my attention?

[vol.2]

To add to the last post. This waveform is shown in the Service Manual here, and it shows that it's supposed to have a symmetrical top portion. Also of note is that the DC voltage on the output of Pin 5 is called out as 4.6V in the SM, but it measures 8VDC with a DMM.

The output of Pin 7 is also incorrect; it's a smooshed sawtooth looking thing and nothing like what it is supposed to be. I have to assume something is wrong either on the input side (Pins 1&2) or the output side (between Pins 7 and 5, or further downstream from 5).

I see the basically correct symmetrical 6.4VDC on pins 1&2 (SM says 6.5, but that's pretty close I think), but the parabola is driven by current and not voltage, so I'm not sure if just having those two correct voltages is enough, and I'm not sure how to tell if there is imbalance in the current draw (or what to do with that information if I had it).

I've followed the output as far as the last set of transistors in the Pincushion circuit (which control the Pin Balance), and the voltages at those transistors appears to be correct.

[vol.2]

I am still bewildered by the Pincushion issue, but I found an area of the circuit that seems to be a little amiss.

There's some readings that are what I would call "shaky," or that they bounce up and down a bit on the scope and are hard to lock in with the trigger.

Also there are some areas that the voltages are a little bit off; nothing is extremely off, but there are some spots that look about 1V or so off.

The "worst" of these spots is around Q312, which is supposed to be 9V on the collector, but it's a little above 10V and bounces around up and down. The base is supposed to be 3.9V, but it's 3.3, and the emitter is supposed to be 3.2V and it's 2.7V.

Normally, this wouldn't look like a smoking gun to me (and it doesn't really), but I'm not seeing anything else much wrong still, and it's right in the "Side Pin" circuit, which is a prime area that looks to be malfunctioning.

I'm sure I am measuring the circuit with the correct conditions (31kHz, color bars), and everything else on the DA board is almost dead-nuts under these conditions, so I believe I have it right.

So I ordered up some 2SC1632's and I'll start off by replacing Q312 and see if that helps. If it does nothing, I can try Q311, 314, and 315 as the are all in the same circuit and all have a tiny bit of voltage variation from the SM, but none of them are more than Q312 is.

This is my readings. Green is dead-nuts, Yellow is slightly off in some way. The yellow circled resistor values are all in circuit, so I expect them to be off. Of course, if any of those looks weird, then please let me know. Sorry it's so messy, but that's how I've been keeping track of things.