[time-nuts] HP 3586B Power Supply Failures

David davidwhess at gmail.com
Thu Mar 22 15:39:43 UTC 2012


I just went through this exercise with a pair of Tektronix PS503A
power supplies which differed in manufacturing date by 10 years.

On Wed, 21 Mar 2012 21:55:39 -0700 (PDT), Perry Sandeen
<sandeenpa at yahoo.com> wrote:

>The other day I had my second HP 3586B power supply board smoked.  It burned both the PC board traces and the connector on the motherboard so badly it will have to be replaced.  Also an inch or so of one trace on the mother board but it looks like it will be repairable.  Fortunately I have a donor board for the connector but it will probably be an all-day project to do the repair properly.
>
>An observation.  There AFAIK a fold-back current limiting circuit but it didn’t help and the correct value of primary fuse did not blow.  This made me an extremely unhappy camper.  I’m also going to try and figure out how to add additional fuses.  
>
>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.)  

The inrush power will be larger but the current may be limited by the
circuit impedance.  The risk is that the rectifiers may not be able to
handle the larger surge current.

I used standard snap-in capacitors with the same diameter to replace
the aluminum can style capacitors.  They were about 1/4 the length but
could use the existing mounting hardware.

>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?

The late Tektronix PS503A power supplies replaced the 4.7uF solid
tantalums with 10uF aluminum electrolytics.  When I was pouring over
the specifications of the Sprague 199D tantalums they originally used,
I found that in the general case, an aluminum electrolytic of twice
the value had roughly the same dissipation factor.

>Additionally, I plan on doing the same to all my vintage HP test equipment.  A smoked 5370B would really, really, really, ruin my week.

I have had a couple of shorted tantalums but never with the dire
results you experienced.  In your case, I might change them all out as
well.



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