I checked the DC recovery diodes in the HV supply as listed in other thread
(all under the plastic cover and they are ok.
Any other suggestions?
Note that checking the leakage of those diodes is important, just a DVM diode check doesn't discover problems.
It looks like the behavior of your 485 is different in different settings. As the first issue are you debugging the intensity? Do you have too bright, or too dim brightness, does intensity control make any difference?
HV supply voltage of 2000V is low. What is the impedance of your 1000x probe? Looking at the schematic ¡°CATH REG¡± can only adjust ~ +/-100V so this is outside adjustment range. Should be the first thing to fix since everything else with intensity depends on it.
Feedback loop around U1624 uses +50V at the top of R1642B as the reference. Is +50V correct?
If you look at pins 2 and 3 of U1624 what voltage do you measure (should be essentially the same and close to 0V).
Once you fix the HV supply if intensity is still problematic:
There are multiple posts about DC restorer issues I recommend you search "DC restorer" "Grid Bias" for useful information.
The ones I know well are: Topic #180156: Although different equipment, this topic has some DC restorer debug. Topic #180235??is a 485 with intensity control issues. In particular looking at the circuitry around intensity control pots. If you review both chains from start there is some relevant information.
For time base issues, in the problematic 3 fastest settings how does the "A Sweep" and "A gate" signals look? They are easily available at the back of the scope with a BNC connection.
Ozan
