DEC H7260 PSU fault

[Rob Jarratt]

> -----Original Message-----
> From: cctalk [mailto:cctalk-bounces at classiccmp.org] On Behalf Of Jules
> Richardson via cctalk
> Sent: 25 January 2018 23:07
> To: xx Classiccmp mailing list <cctalk at classiccmp.org>
> 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
the
> DEC p/n or the Astec AA13010 one), but perhaps they're buried in
schematics
> 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
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
;-)
> 
> cheers
> 
> Jules