Beckman 9100 scope with trace problem #2

AlbertHall

Joined Jun 4, 2014
11,317
I have the same scope, same problem. No trace, I think it may be something in the high voltage transformer, flyback transformer? No experience in working on a tube like this is there any precautions I need to make?
If you also can get a trace by putting a signal on the Z input then the EHT part is working.
 

AlbertHall

Joined Jun 4, 2014
11,317
If you can determine what voltage the power supplies should be (may be marked on the board or connectors) then check them first.
 

KeithWalker

Joined Jul 10, 2017
1,789
I have the same scope, same problem. No trace, I think it may be something in the high voltage transformer, flyback transformer? No experience in working on a tube like this is there any precautions I need to make?
The CRT anode can hold a static high voltage charge for a long time. If you touch it, you will get a nasty shock and your reflex could damage the scope.
In many scopes the cathode is biased negative with respect to ground. The filament is usually powered by a transformer winding that is grounded. When the CRT ages, the filament to cathode insulation often breaks down. This changes the bias on the tube and effects the brightness of the trace. That is probably what is wrong in your case If you can get a trace by applying a voltage to the Z axis.
I had a similar problem with my 50 year old HP 182A scope. I extended its life by rewiring the CRT filament to the ungrounded 6.3V winding of a separate small power transformer.
This may solve your problem and extend the life of your scope. Make sure you measure the existing filament voltage and use an appropriate transformer. The filament current will only be about 0.5A or less.
 
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