Quote:
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?
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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.