Same problem with neon-choppers as found in the 410C. HP replaced that with a fully solid-state board towards the end of production. I wonder if something similar could be done for the 334A?
Thanks,
Barry - N4BUQ
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----- Original Message -----
From: "Chuck Harris" <cfharris@...>
To: [email protected]
Sent: Tuesday, April 7, 2020 8:52:18 AM
Subject: Re: [HP-Agilent-Keysight-equipment] Anyone out there fix a partially working 334A I need desperately to get
it up and running!
The killer problem I have found with 334A's, is they have an optically
driven chopper that relies on NE2 style neon bulbs, and CdS photo resistors
to do the chopping.
The problem is two fold: First, the neons get smoky inside, and don't put
out enough light to switch the photo resistors, and second, the CdS photo
resistors sometimes fail.
The neons used have a little radioactive material sintered into their
electrodes,
to make them dark fire reliably, and modern replacements don't. And, the
CdS photo resistors were selected and matched for maximum on/off resistance
spread. CdS photo resistors run afoul of the RoHS regulations because of the
Cadmium, and are very expensive, if you can get them at all. It is unlikely
you can find the super wide spread selected variety that HP used.
All of the other problems I have seen have been simple capacitor replacement
issues. The 334A is stocked full of TE/30D style electrolytic capacitors,
and
their rubber seals have pretty much all turned to stone by now.
Replacing the capacitors won't have any real effect on calibration.
-Chuck Harris
Steve wrote:
I have an Hp 334A that powers on and appears to function partially but I¡¯m
not sure what all could be wrong with it. If anyone fixes these units at a
reasonable price I would be interested in having it put back in top notch
shape with a good calibration. I restore vintage hifi and I need to get it
up and going as quickly as possible.
