DEC H7140 (11/40) power supply revisions and general advice?

Josh Dersch derschjo at
Fri Oct 9 23:22:20 CDT 2015

On 10/9/15 9:13 PM, Jay Jaeger wrote:
> On 10/9/2015 10:42 PM, Josh Dersch wrote:
>> Capacitor C4 looks to be involved with the START-UP DRIVE signal
>> circuitry (which drives the relay) so the behavior I'm seeing makes
>> sense if C4 died and took a couple of things with it (or if something
>> else died and took C4 with it).
>> Here's where it gets kind of odd -- I spent some time testing diodes and
>> transistors in the related area near C4 and while doing so I noticed
>> that there are four diodes (D1-D4) listed on the schematic that are
>> missing from my board. "Missing" as in someone clipped them out at some
>> point -- there are just nubs of the leads left.  I'm not sure why this
>> would have been done, but there were a number of ECOs applied to this
>> board (a few wires and resistors added) and I don't want to assume that
>> if I just put four new diodes in that it won't cause other problems.
>> Anyone know if there were other revision levels of the bias/interface
>> board that would have done away with these diodes?  Anyone have an H7140
>> they can easily crack open to compare?  (It's actually relatively easy
>> to get to, if you can get to the supply...)
>> Thanks as always,
>> Josh
> I have an HP drive (RK05 type packs) whose startup power supply had been
> tampered with in very odd ways - missing parts, etc. (and maybe even
> blown out circuit board traces - I forget - I haven't worked on that
> drive in years).  I seem to recall that it looked like it had failed
> catastrophically at some point.    I ended up wiring in a 24V stand
> alone supply temporarily as a startup supply and got the rest of the
> supply going that way.  Maybe someone did something similar with your
> supply, and then ran out of time / gave up.  Perhaps they clipped the
> diodes out to test them.
> I have an 11/40 and an 11/45, so I probably have an H7140 (but I don't
> seem to have a spare anywhere, which surprises me a little, because I
> got parts of another 11/40 at one point), but I recall that the things
> are nightmare-ishly heavy to mount, and there is only one of me, so
> unless the area in question is visible without taking the supply out of
> the rack, I doubt that I can help very quickly.

Oh crap -- I just noticed that the subject line says 11/40; it's 
supposed to be *11/44*.  Fingers faster than brain (as is usually the case.)

As you may imagine, the 11/44 has a completely different supply than the 

- Josh


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