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Old 10th Jun 2018, 9:21 pm   #1
RichardHowells
Triode
 
Join Date: May 2017
Location: Swindon, Wiltshire, UK.
Posts: 22
Default HP 175A Oscilloscope - Vanishing Trace

Hi All,

My aged 'scope has stopped working. When last used (some months back) it was fine.

Today I had no trace at all - or so I thought. Further fiddling showed that sometimes - it seemed random at first - I could get a trace. It would only appear shortly after switch on and it would only last a few (maybe two) minutes, before fading out. It definitely faded away over a few seconds rather than instant vanishing. Now it seems to be completely sulking. I can't get any trace at all and I cannot reproduce the fading behavior.

I have the manual with full circuit diagrams, but I am very wary of measuring round the HV circuitry. The rails round there are -2700DC and -2900DC. My highest voltage device is an AVO model 8 with a 2500DC range.

The EHT line is +9300, presumably making a handy 12KV between there and the -2700 rail. I really don't want to go near that.

So - are there lower voltage things that might be relevant culprits?

What are my safe options for measuring around the -2700Volt area?
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Richard
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Years of software, and I still like the occasional soldering job.
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