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Old 10th Jun 2018, 10:16 pm   #2
factory
Octode
 
Join Date: Jul 2009
Location: Cheshire, UK.
Posts: 1,706
Default Re: HP 175A Oscilloscope - Vanishing Trace

Have you checked all the obvious stuff like the main power supply rails, fuses and does the beam finder button do anything?

What is the first part of the serial number for your scope?
The early ones (prefix 235) and later ones (prefix above 344?) differ greatly in the physical design of the HV section.

You can see if the HV oscillator is running by looking to see if the filaments are lit on the four 1X2B valves (they may be hard to see as they are quite dim).
If they aren't lit you could start by checking the voltages around the regulator & RF oscillator valves, as well as checking (with power off) the high value resistors for the focus & intensity haven't gone open circuit.

I have three of these scopes myself, the early one still has the intermittent fault with the HV.
One of the two later ones had an open circuit CRT filament, I managed to find a replacement to get that one working and the other also had no HV when I acquired it, this was cured by cleaning the dirt from the HV section.

David
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