Pincushion Issue on Sony CRT Monitor

[vol.2]

I have been fighting with this CPD-1604S for a couple of months now, and I am at a point where I feel stuck and I need help.

When I picked it up, it did not turn on. I tested every single electrolytic in the set and replaced everything that was bad. A good 2/3s of the lytics were quite bad (more than 50% out and 100kohm+ ESR) and needed to be replaced.

Specifically, there is a kind of daughterboard PCB in this unit that handles deflection control. It's Sony's solution to the Multisync thing at the time, allowing it to "bin" the incoming signal by horizontal refresh rate and provide separate size controls for each one. This board (and only this board) was covered in early surface mount electrolytics that of course leaked out as they all do. I won't get into the details, but I treated and cleaned the PCB correctly and inspected the traces under a microscope. Everything looks good and I get continuity on even the worst effected areas. There doesn't appear to be any major corrosion, only the solder mask has come off in a few spots.

When I put everything back together, I found that I had vertical collapse. I traced the collapse back to the 24VDC power supply that feeds the Vertical output IC. It had a blown fusible resistor. Replacing the fusible resistor restored the Vertical completely, but the sides are wavy and no amount of geometry controls fixes them.

I turned my focus back to the DA PCB. I did a number of things.

- removed all the geometry pots and ensured they have smooth operation

- tested waveforms around IC301 (Horizontal Oscillator) and IC303 (Pinamp Control, called an "East West IC" in the datasheet)

-checked many resistors for values around the Pincushion circuit and for trace continuity

The only obviously "bad" waveform I found was at the output of Pin 7 on the Pinamp IC. Instead of a 500mV parabola, I'm seeing more of a noisy-looking sawtooth wave at about 280mV with a very quick spike of almost 1Vpkpk right in the middle.

The actual output pin of IC303 is Pin 5, and it basically looks like what the service manual says it should. It's the correct voltage, and it's a square wave. I guess I have to assume that it's slightly off and that the pincushion adjustments make on very subtle changes to the square wave that are hard to see on a scope if you don't know exactly what you are looking for.

The Pin Phase control seems to be doing what it's supposed to do, as I can push it to one side to compensate for the Side correction issue, but no matter what I do, it has a significant dip near the bottom sides of the screen. It seems to just be the "Side Pin" controls and the "Pin Up" Controls that aren't responding correctly.

After not finding anything obviously wrong, I tried replacing IC303 (East West IC), but it didn't change anything at all.

I think perhaps this issue could be related to the blown 24V source fuse from the main PCB; it's possible that whatever happened to the fuse might have taken out another component along the way.

This is not the biggest or most complex PCB, but it's filled with tiny surface mount parts that hard to test, and I haven't tried to remove any of the tiny diodes or transistors yet. I have done a little in-circuit testing of things, but I know that's not ideal.

Can anyone offer guidance based on the bad waveform I'm seeing on Pin 7 of IC303? If I had a narrower field to investigate, I might make some progress.

TIA

If you right-click on one of the images and view it in another tab, it will allow you to expand the schematic and see it in detail. I attached the full Service Manual as a PDF and the Datasheet of IC303.

[wasedadoc]

Are you saying that the picture width is not the same from top to bottom? That requires a correction waveform at field rate. Possibly that would come from circuitry dependent on that 24 volt rail which was missing. Did you just replace the fusible resistor or did you investigate why?

[vol.2]

Are you saying that the picture width is not the same from top to bottom?

Yes, completely so. The best I can get the sides is something like this:



When I tweak the Side Pin controls or the Pin Phase control in the other direction, the best it looks is something like this:




There is no in-between or "happy medium" that can be attained.

That requires a correction waveform at field rate. Possibly that would come from circuitry dependent on that 24 volt rail which was missing.

That's why I was thinking there could be something wrong with a component on the DA PCB (small deflection board). Perhaps something that is fed by the 24V rail got damaged when fusible resistor blew up.

Did you just replace the fusible resistor or did you investigate why?

I did my best to check components downstream from the 24VDC source, but nothing looked obviously wrong, and the components I tested were fine. I came to the conclusion that any number of bad caps could have caused the fusible resistor to blow. The set wouldn't even turn on, and I didn't want to leave any really bad caps in the circuit to endanger other components before I switched it on again. I thoroughly tested all of the caps with a good LCR meter and only replaced stuff that was clearly bad. There were maybe 2 caps that were about 25% out of spec that got replaced, but everything else was either totally dried up or more than 50% out and extremely high ESR (all tested out of circuit).

[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.

[amyk]

Yes, completely so. The best I can get the sides is something like this:



When I tweak the Side Pin controls or the Pin Phase control in the other direction, the best it looks is something like this:

Do RV309 and RV310 have the effect described in the manual? As far as I can tell without a deep examination of the schematic, the latter (Side Pin) is supposed to correct for nonlinearity while the former changes the overall amplitude difference between the top and bottom of the v-scan to correct for keystone. Your top image suggests RV310 is out of adjustment while the bottom suggests RV309 needs adjusted.

[suntime]

Hi,

Are the adjustment trimpots/potentiometers good, with the correct ohmic value?

[vol.2]

Yes. As I stated in my first post in the bullet points.

 

- removed all the geometry pots and ensured they have smooth operation

[vol.2]

Do RV309 and RV310 have the effect described in the manual? As far as I can tell without a deep examination of the schematic, the latter (Side Pin) is supposed to correct for nonlinearity while the former changes the overall amplitude difference between the top and bottom of the v-scan to correct for keystone. Your top image suggests RV310 is out of adjustment while the bottom suggests RV309 needs adjusted.

The Side Pin (L) (RV307) and Side Pin (H) (RV310) pots do not have the stated effect. They do not correct the side. They just kind of squish it into a barrel shape if I turn them to the right far enough. The image looks "best" with both Side Pin pots turned all the down to zero so the wiper is out of the circuit. If I turn either one of them all the way to the left, it renders the other one completely without effect.

The Pin Phase (RV309) seems to get closer to the stated effect; it basically does trapezoidal adjustment (narrower on the top VS wider on the bottom and vice versa), but it will not ever fully adjust the image to be straight on the sides, and the other pots Side Pin L, H and Pin UP do not do enough to help compensate for the sides at all.

Whatever is going on, it's not a misunderstanding of the Pincushion controls. I am sure that something is wrong and it's preventing me from dialing in the horizontal geometry.

I believe that the issue is related to the parabola generation in IC303, because I'm not seeing the correct parabola on Pin 7; in fact I'm seeing no parabola at all. That means the current driven comparator on Pins 1 and 2 is somehow not getting the correct input, but I'm unsure the source of this fault.

[suntime]

Hi,

In the past when I repaired CRT TVs I had 5 TVs (Panasonic & Sony) with E/W deflection problems and they were fixed by replacing the TEA2031A.

Regards.

[FIXITNOW2003]

Long time since i have seen one off these .only have these notes
CPD1604S   that displays its image as trapezoid a shape.  Any adjustment I make only lasts until power off and shifts the narrow part from top to bottom   check all the SMD caps for leaking or high ESR Also check all the SMD electrolytics for bad ESR, but don't stop there. These caps will sometimes leak fluid that can eat traces and vias underneath the caps, chances are there are several bad ones that need replacing. Esp.  check C328 and C334, also IC303 = TEA2031A. Clean the board well of any leaked electrolyte, repair any damaged PC traces, and run wires through any damaged through-hole connectors underneath these caps. Readjust RV309.   
CPD-1604S   no picture, unit makes humming noise.  Horizontal output ok.   Try checking/replacing capacitor C911 = 10 uF, in the power supply.   
CPD-1604S    Pincushioning & Vertical Collapse after being on a while   Reflow Main & CRT board.   

[vol.2]

Long time since i have seen one off these .only have these notes
CPD1604S   that displays its image as trapezoid a shape.  Any adjustment I make only lasts until power off and shifts the narrow part from top to bottom   check all the SMD caps for leaking or high ESR Also check all the SMD electrolytics for bad ESR, but don't stop there. These caps will sometimes leak fluid that can eat traces and vias underneath the caps, chances are there are several bad ones that need replacing. Esp.  check C328 and C334, also IC303 = TEA2031A. Clean the board well of any leaked electrolyte, repair any damaged PC traces, and run wires through any damaged through-hole connectors underneath these caps. Readjust RV309.   
CPD-1604S   no picture, unit makes humming noise.  Horizontal output ok.   Try checking/replacing capacitor C911 = 10 uF, in the power supply.   
CPD-1604S    Pincushioning & Vertical Collapse after being on a while   Reflow Main & CRT board.   

Hi, thanks for your comment.

I am working on the DA PCB now for electrolyte washing. I replaced all the electrolytics on that board when I first got it, but I think I missed some surface mount components that had electrolyte trapped underneath them. This board is filled with SMD transistors and such and is taking a long time to repair now.

When I'm done, I'll see if that is the fix, most probably is.

Thanks @suntime, I already tried to replace the TEA2031A and that made no difference. I've gone back to more PCB treatment. It's a long slog.

[bostonman]

It's been many years since I worked on CRT monitors, but usually such problems were electrolytics.

Try a hair dryer (or heat gun) and see if the problem gets better.

[vol.2]

It's been many years since I worked on CRT monitors, but usually such problems were electrolytics.

Try a hair dryer (or heat gun) and see if the problem gets better.

Unfortunately, I ended up having to remove a large number of surface mount components to clean underneath of them and inspect things for damage. I found a couple of possible causes for the issue including a cracked resistor (that was still reading the correct value, but might have been experiencing issues under load), and a more heavily damaged area of the board that two transistors with corroded legs which kind of crumbled off when I removed them; they were still in circuit and voltages were mostly correct when I pulled them out, but they were clearly corroded on the inside somewhat and therefore could have been creating some weird effects.

The issue with this repair is that it isn't a "smoking gun" kind of situation where I can find a single bad part and match it to the symptom. Because the circuit is "mostly" working, it's just one specific area that is having issues, and the issues are related to current and not voltage. The only bad waveform I can find is Pin 7 on IC303, which suggests that the Sawtooth on Pin 1 is current limited, and indeed there is a slight amplitude issue on the waveform. It's not enough for me to have thought anything of it, but I had someone point out that it's a crucial spot to the effect of the circuit. If there is enough parasitics in the circuit leading up to Pin 1, the current balance will be off and the Pincushion controls will not function and viola.

The assessment was that there is 1) enough residual electrolyte on the surface of the PCB to make it conductive and create effects between the pins of transistors in the Pincushion circuit and/or 2) enough components have a small amount of damage from the electrolyte to create extra resistance in the circuit and current limit Pin 1.

I removed all the components from the effected areas including the areas involved in the Pincushion stuff, washed the board with warm water for a few hours and dried it thoroughly including a second wash with IPA to drive moisture out of nooks and a heat gun.

I've got replacement transistors and a bunch of high accuracy resistors to replace almost everything, so I'll just do that and cross my fingers.

If I do that and the fault is the same, at least I'll know what it isn't. I suppose if the fault is the same, it will probably turn out to be a broken trace I missed somewhere, or a broken via given that it's a double sided board.