DEC H7260 PSU fault

Jules Richardson jules.richardson99 at
Thu Jan 25 17:06:56 CST 2018

Hi all,

I mentioned this in the thread where I'd asked about basic Microvax II 
info, but it may have got lost in traffic...

The machine's H7260 PSU is somewhat unwell - one of the internal +5/12V 
supplies appears to be healthy, but the other has outputs which are sitting 
at around 2.5V (both on the 5V and 12V rails) under a test load.

Initial questions...

1) Are schematics are available online? I couldn't find them (either under 
the DEC p/n or the Astec AA13010 one), but perhaps they're buried in 
schematics for a specific DEC machine somewhere.

2) Upon initial glance, the 'first' board of the three in the PSU module 
appears to be a pair of control relays, bridge rectifiers and capacitors, 
supplying +/- DC voltages to the two individual PSU boards. Does anyone 
know if I can disconnect these from the PSU boards safely* and measure 
their outputs, and if so what voltages I should expect to see? That might 
be a good initial test before pointing a finger at the PSU board associated 
with the low outputs.

* I mean without component damage - I expect they might be sitting at a 
significant DC voltage, so there's an obvious personal safety aspect too ;-)



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