I will try to replace it with a 40 volt supply, but I currently don't have one unfortunately. Just following the voltage, A18 prereg board gets mains 250VAC but seemed to output 0VDC, peaking at 2VDC when I hear the sound. However, that was with one probe on P803 and another in P804. Measuring between P803 and chassis results in -104VDC?
This should be 45V or 43 as you say. And I don't know why it's negative. COM probe was on chassis GND, and P803 is marked as +.
In the midst of all this, while measuring, I suddenly hear the normal HV tone, then see a trace???
it was strangely... fine. Then started pulsing just like the first time, and currently is doing the same old thing of not working. I tried checking if the HV multiplier was making the noise, by disconnecting P803 and 4 which I believe will disconnect power to pretty much the whole scope, making A18 and a bit of A10 the only powered parts. When turning it on, it made the same sound, so I believe the HV multiplier is not necessarily it.
Current limit the 43 volt power supply to well under 1 amp, as the pre regulator will do the same if there is any fault in the multivibrator power circuit or derived voltage (-8.6, + 8.6, +5, +30 and +100)
There are wire jumpers 975, 965, 985, 966 that can be lifted for down-stream trouble shooting.
Also the HF, HV wire to U990 HV multiplier.
Lift one jumper at a time until the rest V's become normal.
Watch that last one, 2KV at 22 KHz.
Do you mean W975 and so on? Those look to be resistors, I couldn't find any jumpers.
Sorry for being clueless by the way
I also checked pin 12, Vcc, of U920 in A18. This, according to the datasheet, should be given a max of 41V. It measures at -100V as well