Sony KV-9200 Uneven Raster

[vol.2]

Originally Posted by Alex KL-1

1.6V with the set on? Very strange. Or the DMM are playing havoc with superimposed waveform, or really it have something fishy in Denmark...

If I am correct in assuming that Q512 is not conducting properly, then it's bringing the voltage down on the other side of L508.

The fact that it isn't conducting would be creating other complex paths to ground for the 112V present on the other side of L508, because the failed transistor is not letting current flow through L508.

Essentially, the current through L508 needs a path to ground to follow, but with Q512 dead, it can't reach the emitter of Q512, which is that path.

That's the way I understand it, but I'm far from an expert.

I think maybe Zeno could answer better, but I can promise that I'm not seeing any 108V on the collector of Q512. I have several multimeters, including an all analog one, and they are not seeing it. Measuring Q512 out of circuit reveals that it is *extremely* weak and the forward voltage is quite low on the collector junction specifically.

I would guess that this is a fairly common occurrence, since the HOT is getting hammered on constantly during scan time.

[vol.2]

Okay, well I replaced Q512 and it didn't help.

I realized my error here that the collector voltage on the schematic was actually an integrated AC waveform, and not a true DC voltage. At least that's what I believe is the case now.

It was confusing to me because sometimes my DMM told me it was 2VDC and sometimes it told me it was ~114VDC, even when in explicit DC mode.

Additionally, I assumed that it would match the RMS voltage calculated by my scope at about 265VRMS, so I guess the DMM is doing some kind of voltage averaging or something like that idk.

At this point, I am not sure what to try anymore.

The basic symptoms are still there

- Low horizontal and vertical size

-Horizontal center is shifted too far to the right, can barely compensate with horizontal centering control

-Hourglass distortion control is biased to pucker in on the sides. Adjusting it never evens out the side completely, but it does pull in the corners.

That's about it. Everything else seems pretty good about the set. The picture gets bright and has decent sharpness for a 1978 tube.

I have measured the B+, the yoke, flyback and HOT windings and they all seem to be good. I measured the size and geometry pots and checked voltages around the deflection area.

My last thought is that maybe the Damper Diode is weak? Not sure if that could cause all this, but maybe.

[vol.2]

Replacing the damper diode didn't help the hourglass distortion, but it did increase my horizontal deflection signal by quite a bit. It was definitely weak. For some reason, this actually helped to make the picture look noticeably sharper, so that was worth doing.

I found what I think is the problem with the geometry now. There is a coil on the rear yoke assembly that the service manual calls "PIC". This is connected in parallel with another inductor and then in series with the main H Yoke. The PIC inductor is wrapped around a plastic ring and placed around the rear of the yoke. The other inductor is a little guy that is mounted next to the main front yoke.

I found that the PIC inductor is low by about half. It's supposed to be 0.48 ohms, but it is about 0.22ohms (taken out of circuit). After looking at it carefully, I realized that it is stuck in place with the same brown glue as was on the rest of the PCBs and had gone conductive and corroded a lot of the capacitor legs and stuff. I got it off of everywhere else but here.

Here is the yoke I'm talking about and the position in the circuit from the Sams.

Does anyone have an idea how to remove the glue from this inductor without ruining it? I don't easily know how to replace it, and any original part would have the same brown glue on it.








I was able to remove the rear yoke assembly and at least remove the inductor wires from the glue where they join together at the terminal strip. This raised the resistance from a consistent 0.22ohms to a consistent 0.26ohms. The brown glue is all up and down both sides of the coils, so I am fairly confident that this is what happened with the spec of the coil. I don't know if this will actually improve the hourglass distortion, but the inductor appears to be labeled as something that controls the pincushion correction, so I'm hopeful.

[Alex KL-1]

Anyway, this is really possible; a corrision. But the wires are so apart so is worth to check the oned that can cross like the ones that go to terminals. Or, the core is rather conductive and with corrosion... (but is easy to check)

[vol.2]

Originally Posted by Alex KL-1

Anyway, this is really possible; a corrision. But the wires are so apart so is worth to check the oned that can cross like the ones that go to terminals. Or, the core is rather conductive and with corrosion... (but is easy to check)

I pulled the whole thing apart and I removed the brown glue.

There was a fair amount of corrosion happening around the top of the coils, especially where they crossed the bottom side of the terminal strip. I scraped it all off and all the brown glue.

Unfortunately, this didn't seem to be the problem. When I got the coils out and measured them, I found that each side was 0.48 ohms exactly, so I'm convinced that the Sams was giving the DC resistance per side and not the whole thing. This was with all the glue gone and no coils touch each other at all; this inductor is wound very loosely and doesn't overlap.

So I don't know what to do now.

Another symptom That I didn't think to mention is that when I change the horizontal size, the brightness of the raster changes. It gets darker when make it smaller. Pretty significantly darker actually. Now that I think about it, this seems fairly significant and wrong.

[vol.2]

So I found that the boost voltage derived from the Horizontal Yoke pulses is quite a bit too high. In order to get the width to cover the whole screen, I end up with close to 600V boost, when I am supposed to be getting around 500-530V.

When I changed the width, it changes the boost voltage, and the boost voltage feeds the G2, which is why changing the width also changes the brightness.

I don't really understand this. Is it by design?

Should the loading on the boost rectifier determine its voltage? And if so, should it be this wide of a margin?

You can see here where the boost is created. I assume it's rectifying the H yoke pulses as there is no other source I can see.

[Alex KL-1]

Originally Posted by vol.2

So I found that the boost voltage derived from the Horizontal Yoke pulses is quite a bit too high. In order to get the width to cover the whole screen, I end up with close to 600V boost, when I am supposed to be getting around 500-530V.

When I changed the width, it changes the boost voltage, and the boost voltage feeds the G2, which is why changing the width also changes the brightness.

I don't really understand this. Is it by design?

Should the loading on the boost rectifier determine its voltage? And if so, should it be this wide of a margin?

You can see here where the boost is created. I assume it's rectifying the H yoke pulses as there is no other source I can see.

This circuits are very tricky and interactive ideed; no much ideas, but...
Compensation of bright according with beam current or even H size is seen. But, if so, the circuit responsible for that was...?
Is easy to see how H size reduced have more bright due to less area for same total beam distribution.
Something are definitively interacting and playing havoc. It must be in a circuit that controls the sweep current, but where?

Even T502 can cause havoc but with such symptoms, something are draining more current with smaller size perhaps?

[vol.2]

Originally Posted by Alex KL-1

This circuits are very tricky and interactive indeed; no much ideas, but...
Compensation of bright according with beam current or even H size is seen. But, if so, the circuit responsible for that was...?
Is easy to see how H size reduced have more bright due to less area for same total beam distribution.
Something are definitively interacting and playing havoc. It must be in a circuit that controls the sweep current, but where?

Even T502 can cause havoc but with such symptoms, something are draining more current with smaller size perhaps?

T502 seems okay, it measures correctly out of circuit. I think maybe, maybe it's the fault of the flyback winding that feeds the HOR output?

The service manual says the winding should be 0.05ohms, but I get 0.038ohms.

I honestly wouldn't think it's a problem normally because it's such a low resistance that probe issues could be a problem, or slight manufacturing tolerances. However, I'm seeing a low Horizontal signal at the base of Q512 as seen in this figure of the Sams. If we are taking for granted that the Sam's is correct of course. The Sony SM doesn't have a waveform at this spot, so it's hard for me to know for sure. Also, the waveforms on either side are in the ballpark. The collector of Q511 (feeding the flyback primary) is correct and the damper diode has been replaced. The amplitude of the collector of Q512 is basically correct, but it fluctuates depending on the width control (higher and lower than the target 750Vpk).

You can see these waveforms around the flyback in an earlier picture. The 32Vpkpk waveform at the base of Q512 is only about 22Vpkpk. Could be a mistake in the Sams?

However, the screen width is too narrow. I have to almost max out the width control to fill the screen.

Also, I have realized that the raster has horizontal fold-over. I noticed this while performing a horizontal OSC setup. I shrank the screen so I could see the edges, and I noticed there where retrace lines banding vertically on the left side of the screen. While in adjustment mode and the image was horizontally scrolling, I noticed that the image was rolling over on itself on the left when it hit the retrace lines.

So this is a width issue, but also a linearity issue.

One idea I had was the detector diodes in the Phase Detector area of the circuit. That feeds back into the horizontal output section. Perhaps if those germanium diodes are messed up enough, the imbalance in the phase detector could be causing a cascade failure of the linearity?

The detector diodes are here. The waveforms on either side of them are about correct at ~11Vpk, but the waveform between them is low and looks like about the same 11Vpk, not 14Vpk. That is ultimately driven by T502, but it also connects back to the rest of the horizontal circuitry, so I could believe that it would be wrong if the diodes are super weak or the matched pair has gone way out. I measured them out of circuit and their reverse leakage is like 350kohm for one and 550kohms for the other, so I guess both are "working", but I don't know if that's good enough for this location.




Also potentially of interest is the collector of Q503. In the Sony service manual, it shows a 6Vpk square wave with a flat top on it similar to the waveform shown here on the base of Q504. When I measure the collector of Q503, The waveform has a big slant to it, going up to the left. When I check the base of Q504, the slant is gone and it shows a flat top.

It strikes me as an amazing coincidence that I am seeing this slant in that spot, and there is a linearity issue.

[Alex KL-1]

A bad driven HOT can cause issues. Normally this acts a switch. An driver error and timing gets wrong. Remembering that H circuits are tuned (at least flyback), so, a wrong timing affects linearity; Gross errors explodes the HOT. Hosc and driver can be suspects in this case.

[vol.2]

Originally Posted by Alex KL-1

A bad driven HOT can cause issues. Normally this acts a switch. An driver error and timing gets wrong. Remembering that H circuits are tuned (at least flyback), so, a wrong timing affects linearity; Gross errors explodes the HOT. Hosc and driver can be suspects in this case.

I've investigated the driver transistors, and I can't find anything funny there. However, I've found that Q501 has a funny voltage.

Q501 is supposed to have a negative voltage (-0.2V) on the base, and yet it has about 1.8V. When I measure the source, it's all correct voltages before the base.

In this case, I assume that the transistor is switched off, and something beyond the collector and emitter is supposed to be sinking current, keeping the base at a negative voltage.

The only thing there I see wrong is the amplitude of the waveform between the phase detector diodes. It's supposed to be 14Vpp, but it's like 10.5Vpp.

I don't have any replacements for the germanium diodes in stock, but I ordered something that should work, so I'll replace them and see if that helps.

[Alex KL-1]

10.5V of amplitude here explains pretty much about image size. Even if C558 is dry perhaps this occurs (bad HOT biasing in cutoff).
About base of Q501, either sync amplitude and HOUT amplitude will affects if it will rectify excess amplitude (and provokes the desired negative base voltage). But any R, C or diode can be culprit in the path. Or, simply the flyback have a very unusual fault and behaves like it are mistuned..... then a experimentation with C560 (the resonant cap one), adding a little or subtracting a little (put a 2nF/1.6kV poliprop in parallel with it), to see if pulses rise. But I advise to try to find the driver cause first.
I just remember to made this in the past in one misterious behaving TV.

[vol.2]

Ok. So it took me awhile to get back to this because I accidentally blew the main B+ regulator and I had to get another one.


However, I have done a bunch more troubleshooting and made some discoveries, and settled on a problem to fix (or attempt to).

Essentially, the problem is that the horizontal width is too narrow. Replacing one or both of the HOTs (on either side of the flyback) doesn't seem to help things, and the voltages are largely okay. To make this completely clear, in order to make the image fill the screen horizontally, the HORIZ SIZE pot must be almost all the way to one side.

When I change the HORIZ SIZE pot, the brightness (G2) of the screen changes dramatically. The wider the raster, the brighter the screen.

The difference is significant enough that a slight change would require adjusting the screen voltage to compensate.

In this image, you can see the voltages on the PIN MOD transistor Q505 when the image is properly filling the screen. If I back off of the size, the voltage will go down to what the Sam's say it should be, and the raster become dark. I also noticed that the difference between the Base and the Emitter of Q505 is consistently 600mV and not 1V as it says on the Sam's. For example, when I set the HORIZ SIZE so that the Emitter is 109V, the Base is 109.6V. I changed out Q505 for a new part and it's behaving exactly the same way.