13 Apr
2009
13 Apr
'09
7:10 a.m.
I managed to get the +15V line back, and so I also have -15V. Found an
open diode and a bad power transistor. Replaced them both and it's
working again.
Still no life from the CPU, but I just noticed that ACLO and DCLO are
asserted, which I understand can cause this kind of misbehavior. (This
was happening before I broke the +15V line, I just didn't realize that
ACLO & DCLO are active-low signals at the time when I was testing out
the supply...) Guess I get to pull the supply again and do some more
debugging :). Is there a quick 'n dirty way to fake out/bypass these
signals so I can at least see if the CPU runs at all?
Thanks,
Josh
Josh Dersch wrote:
So I'm now the proud father of a DEC PDP 11/40,
which should be a fun
project/adventure to get running again.
I have been testing out the power supply and everything looked good
this morning, at which point I figured I'd populate the CPU backplane
and see what would happen. The answer is: not much -- occasionally a
few LEDs would light up, but the machine was completely unresponsive.
I went a bit further and tested the voltages at the backplane, and
while checking the +15V, my probe slipped momentarily, bumping a
nearby wirewrap pin, causing a small spark. Now, where I once had
+15V, I have 0V. And since the -15V regulator is powered (in part)
from the +15V line, that's dead too.
I was hoping, after reading through the documents again, that it would
be something as simple as fuse F1 on the power control board, but no
such luck. The fuse is still good.
Any suggestions for what's most likely to have blown when I screwed up
here? Any recommendations for working on this supply? I'm really
looking forward to pulling this thing out of the rack to work on it --
this thing looks heavy :)
Thanks,
Josh (still slapping himself for screwing this up...)