I cleaned up the HV test point and I get now some 2800V. What makes me
little bit nervous is I don't know if the cause was just the contact
cleaning or if something else have changed. Nevertheless it changed in the
right direction. I think the whole section under the plastic cover needs
cleaning it's covered in black dust.
It may be some conductive residue. HV section have some high M-ohm resistors, any conductive residue will change things. 2800V is low (looking at +50V supply and opamp inputs is still a good debug flow for HV) but probably close enough for intensity debug. Too bright intensity is not good for the screen so it is better to take care of it sooner than later.
I will de-solder the diodes in the DC restorer and measure leakage current.
Before you desolder the diodes, can you check if you can control brightness with "GRID BIAS" adjustment (R1660)? Also, as you change intensity knob, can you control the voltage at "Z OUT DC" test point (TP1781), and at what range?
Ozan
