[time-nuts] HP 3586B Power Supply Failures

John Miles jmiles at pop.net
Thu Mar 22 05:33:49 UTC 2012


> So I went through the entire instrument and came up with a list of all the
> Sprague TVA electrolytics that I am going to replace as they are dated coded
> 1983.
> 
> So two questions.  One, can I safely double the capacitance of the filter
> capacitors?  (I plan on using the 105C 10K hour high reliability Nichicon or
> Panasonic units.)
> 
> Secondly, the tantalum filter caps seem OK but can they be replaced with
> the same high quality aluminum electrolytics perhaps of a higher value of
> capacitance?
> 
> Additionally, I plan on doing the same to all my vintage HP test
> equipment.  A smoked 5370B would really, really, really, ruin my week.
> 

Replacing known good filter capacitors is a zero-sum exercise at best.  New aluminum electrolytics are relatively expensive, and you'll be replacing parts that are probably near the bottom of their bathtub-shaped reliability curves with parts that are definitely on the left side of theirs.    

I did this for a while, but I eventually realized that new "computer grade" electrolytic capacitors no longer have the same quality levels that they must have had in the 1970s and 1980s.  Back then, orders of magnitude more of them would have been used in production than are used today, and the manufacturers would have paid more attention to what they were doing.   After my first few encounters with high-ESR parts out of the retail box, I stopped replacing good ones.  

I have no actual statistics to offer in support of either side of the question, but in my own case, it certainly hasn't cost me anything to leave good electrolytics alone.

-- john






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