25 Jan
2018
25 Jan
'18
3:47 p.m.
-----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