The High voltages are derived from
Unfortunately I cant measure the high voltages because I dont own high voltage probes or test leads. But I think the problem wont be there, since the intensity and focus works and the 3kV ceramic cap are OK
The list of things that can cause focus problems is very short and all of them relate to voltages.
Start by measuring the 58V supply for the EHT converter. Then check the voltage on test point MV11, you should see around 200V peak-to-peak. I am assuming you have an oscilloscope available.
. If it is not ok, common faults are:
- V1103 & 1104 dead
- C1112 leaky/dull (remove and check)
You can get old school DC HT probes for around 30$ on ebay. The ones that look like a parrying dagger. These usually require a multimeter that has exactly 10MOhm internal resistance as they use the meter as the dividing resistor.
If you have bad luck, the BG2000 voltage multiplier on EHT board is dead. These have become increasingly hard to find in the right pin configuration.
Another (albeit theoretical) fault is a too high filament voltage heater voltage. Should be 6,3V. When it's too high, the EHT can collapse as it not able to provide the increased current caused by a too hot filament. This is very unlikely in this unit, as the filament voltage is tapped from the EHT transformer.
Pictures of the screen would be helpful.