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HP 339A Nonfunctional Auto-Nulling
HP 339A Nonfunctional Auto-Nulling
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Old 18th June 2018, 06:10 PM   #1
busaboy is offline busaboy  United States
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Default HP 339A Nonfunctional Auto-Nulling

Pulled out my HP 339A after about a decade of non-use. The notch will not auto null. Oscillator output is connected directly to the analyzer input. I've gone through the various notch circuits using an an O'scope. Unfortunately the manual is a bit lacking in what signals I should be looking for. Can't seem to find anything obvious wrong.

A few clues:

1. Frequency LEDs indicate a low frequency.

2. At 1KHz, the oscillator is putting out 950 Hz.I don't know if the notch will null with 50Hz error.

3. If I adjust the Frequency Vernier to max, I can get a partial null. 20% distortion.
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Old 18th June 2018, 07:13 PM   #2
JonSnell Electronic is offline JonSnell Electronic  United Kingdom
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You will have your time cut out, replacing all of the electrolytics! ALWAYS use exactly the same value components, after all, the designer of the 339 knew a bit more about it than the average DIYer.
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Old 18th June 2018, 09:29 PM   #3
busaboy is offline busaboy  United States
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Quote:
Originally Posted by JonSnell Electronic View Post
You will have your time cut out, replacing all of the electrolytics! ALWAYS use exactly the same value components, after all, the designer of the 339 knew a bit more about it than the average DIYer.
I will look at them. Hopefully there will be some physical evidence. I have a very large lab of test equipment so replacing capacitors is nothing new.

Do you have a reason to make the statement? I've replaced a ton of capacitors based on physical evidence like leakage or being shorted. Any past experience with this HP model that would point to capacitors? I have a lot of HP gear older than this without cap issues.
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Old 23rd June 2018, 01:36 PM   #4
Chamberman is offline Chamberman  United States
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If its been sitting for that long unused then I'd suspect the rotary switches might need cleaning. I bought a 339A used a few years back and it had some weird issues. Those issues disappeared after I cleaned the rotary switches.
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Old 24th June 2018, 07:55 AM   #5
Shinja is offline Shinja  Japan
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CdS optocoupler may be NG. I once repaired old panasonic gear replacing optocoupler. Identical parts are hardly obtainable today. I tried coolaudio VTL5C3 but it make notch tunable range and distortion worse. So I took good optocoupler from oscillator section and put the VTL5C3 there.
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