DEC H7260 PSU fault

Rob Jarratt robert.jarratt at
Thu Jan 25 17:47:47 CST 2018

> -----Original Message-----
> From: cctalk [mailto:cctalk-bounces at] On Behalf Of Jules
> Richardson via cctalk
> Sent: 25 January 2018 23:07
> To: xx Classiccmp mailing list <cctalk at>
> Subject: DEC H7260 PSU fault
> 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
> DEC p/n or the Astec AA13010 one), but perhaps they're buried in
> for a specific DEC machine somewhere.

I doubt it. For the H7864 from the BA23 MicroVax II Enclosure I couldn't
find anything and in the end made my own schematic.

> 2) Upon initial glance, the 'first' board of the three in the PSU module
> 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
> these from the PSU boards safely* and measure their outputs, and if so
> 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
> cheers
> Jules

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