Quote:
Originally Posted by old_tv_nut
You need to look for some voltage that changes when the width jumps. A steady 155 volts may just be due to component tolerances and not something failing.
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Quote:
Originally Posted by Alex KL-1
+1 for watching voltages.
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Okay, I took readings at the 60V chopped voltage with feeds Q403 and to the collector of Q402, which I believe imparts the horizontal drive signal.
I also watched the 155V (160V) during the flash test.
Voltage stayed fairly steady at 155V during flash test. Dipped down maybe 200mV at most.
Both waveforms (Q402,403) stayed completely steady during the flash test. No movement whatsoever.
What was more interesting is that the waveform #2 which is supposed to be 660Vpk is more like 1.1kVpk.
This seems excessive. Although someone else has told me that 1kV is probably normal for a color monitor, even though the SM says 660kV. I don't know what to think about it.
I had to use a 100X probe for the readings on my scope, but both readings were taken with the same scope and probe on the same settings, so unless the scope or probe is somehow going to start misbehaving at a higher voltage, it's accurate (or service manual is wrong).
Quote:
Originally Posted by Alex KL-1
I can add, if PSU caps are good, I fear about the pulse caps in the HOT. Some monitors have switching for different resolutions (adding more cap for lower resolutions=lines), for tuning the flyback, and perhaps one can be "added" at these flash times. But, the image will be dim if this occurs (at the moment).
Also, if image srhinks at that time, can be a failing pulse cap. This can indeed produce/induce a high output voltage from flyback and produces a flash somewhere (depending about the severity of the failing cap).
Investigate it only if voltages are all stable at the flash times.
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I measured all the capacitors in the path of the horizontal yoke and it's related circuitry (basically about 15 or so large film caps between the collector of H OUT transistor and the H Yoke coils). All capacitors are perfect, one cap is 10% out, and the rest are within 1%.