On Mon, Apr 25, 2022 at 07:49 AM, diyguitarist wrote:
If it were HV oscillator coupling, what would be the mechanism by which that
is happening?
The mechanism would be: HV supply feeding into F937 comes from the same secondary winding of the transformer as +12V. You can see the connection across C1142 in sheet <17>. A possibility is one of the caps I mentioned in the previous message (C937 on sheet <16>, C1142 and C1151 on sheet <13>) could be bad, not filtering the HV ripple on the supply, and it is leaking into +12V supply.
Also, although fuse F937 is not blowing, what would happen if
that 500pF "door knob capacitor (C953) was a little leaky? Could that cause
something like this noise to happen?
If your previous observation, pushing display switch between DELAYED SWEEP (B) and EXT HORIZ giving you a clean dot, is still correct the coupling has to be before the horizontal amplifier. We expect some issue downstream, like C953, should still be there even when input to horizontal amp is disconnected (switch at not fully engaged to any input).
If you increase/decrease intensity of the trace, does it change the coupling signal pattern?
Is +75V clean? Any ripple on +75V will show up in +12V and -12V.
Does 10mV ripple has the same burst like pattern, or do you see 2x line frequency ?
Ozan
