Sony KV-9200 Uneven Raster

[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.