DEC H7260 PSU fault

Rob Jarratt robert.jarratt at
Fri Jan 26 01:30:58 CST 2018

> -----Original Message-----
> From: cctalk [mailto:cctalk-bounces at] On Behalf Of Glen Slick
> via cctalk
> Sent: 26 January 2018 01:17
> To: General Discussion: On-Topic and Off-Topic Posts <cctalk at>
> Subject: Re: DEC H7260 PSU fault
> On Thu, Jan 25, 2018 at 3:06 PM, Jules Richardson via cctalk
> <cctalk at> wrote:
> > 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.
> >
> Previously you also said:
> > OK, the top PSU of the pair in this machine appears to be healthy. The
> > bottom one, however, sits at around 2.5V on both the +5V and +12V outputs.
> > That's without any cards, and the card-cage fan / temperature sensor
> > unplugged, i.e. just with my dummy loads in place, so it looks like
> > that PSU has issues (oh, and I tried decoupling the PSU from the
> > backplane and loading it via the drive connector, so it doesn't appear
> > to be a backplane issue).
> >
> Looking here at page 107 of the maintenance print set, BA123-A Basic
> Enclosure Power Harness Wiring Diagram
> Did you disconnect the wiring harness from J10 completely? If you disconnected
> the temperature sensor module or the card-cage door interlock switch I would
> expect that the power supply might not operate normally.
> I forget what the card-cage door interlock switch does, whether it prevents the
> power supply from fully powering up, or if the power supply does fully power
> up but also turns the fans on full blast if the card-cage door is open which
> disrupts the normal cooling airflow.

If the door is open the fans run full blast.

> I would check what my BA123 does, but that would require too much moving of
> stuff about at the moment to get working space around it.

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