9 Oct
2015
9 Oct
'15
9:13 p.m.
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.
JRJ