Sony KV-9200 Uneven Raster

[vol.2]

Originally Posted by Popester

Actually I didn’t think the second photo of the set looked too bad. Some of that bowing of the picture lines you have highlighted look like pincushion circuit issues. Might want to replace electrolytics in that circuit.

All of the electrolytics have been replaced. They all tested way out and some of them were open or had destroyed legs.


In any case, I'm pretty sure I found the smoking gun. If you look at this portion of the schematic, I circled where I found a missing voltage on the collector of Q512. It's called the convergence output on the Sam's, but the SONY service manual calls it the HOT. It's supposed to have a 750Vpkpk signal on it, but it doesn't get anywhere near that high, and it's supposed to be 108VDC, but I only measure ~1.6V. There is about 114V present on the other side of that inductor.

Amazingly, there's enough travel in the screen geometry controls to bring it up to about the correct size when the HV Size are at their full travel, but I think this is why the geometry is messed up, and also why there is an uneven brightness on the raster (because I have to use the HCENT to shift the screen all the way to one side).

I found a transistor to replace it, but it will be some time before it comes in the mail.

[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...

[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.