DEC H7822 power supply

Maciej W. Rozycki macro at
Wed May 11 20:00:24 CDT 2022

On Thu, 12 May 2022, Peter Coghlan via cctalk wrote:

> Anyway, the good news is that I think I have found the source of the
> problem.  One of the capacitors used to filter the (DC?, pulsed DC?,
> rippled DC?, biased AC?) supply to the 9V regulator is marked 330uF/25V.
> It reads 6uF on the capacitance range on my multimeter.  This can't be
> helping the cause.  It's not showing any signs of leakage but it's got
> a brown sleeve and the same logo as the nasty, leaky SXF capacitors but
> it is marked KME.  (I said there was only one capacitor in the filter
> in a previous posting.  Originally I managed to spot a little 10uF/100V
> capacitor but somehow failed to notice the chubbier 330uF/25V capacitor
> completing a PI filter with a small choke...)

 Likely just a general purpose capacitor.  I only have 2 330uF/25V 85°C 
Nichicon SE parts listed for the H7821 (and I have a note about one PSU of 
this kind having a 220uF/35V part in place of one of those too).  Also no 
100V parts at all, but 4 10uF/35V 105°C parts, either Teapo SE or Daewoo 
RS.  Teapo SE and Chemi-con KME series are standard general purpose parts 
and given the low temperature rating Nichicon SE are likely such as well.

 I guess especially for standard capacitors factories ordered whatever was 
readily available whereas with the high-ripple low-impedance/ESR parts the 
choice was much more limited.


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