pdp11/45

From: Jacob Ritorto <jritorto_at_nut.net>
Date: Wed May 26 23:48:47 1999

Hello Classiccmp.
        I recently acquired a nice, rust-free, mostly-original 11/45 from
an old lisp hacker in Los Altos Hills, CA. He told me that it had been
running the last time he'd powered it up, which was in 1984 IIRC, but
sadly, something has gone awry and it won't run now, though it seems to be
close. Here's a brief summary of its status:
        It was originally a five-rack system with each rack containing the
controllers for the housed peripherals. The bus was chained through to
each rack on a BC05 and terminated with an M930. I only took the
processor and the TU-10 racks, so to make troubleshooting easier, I
reduced the system to only the CPU and memory boxes (memory is a 220KB
box from Monolithic Systems that has unibus in and out). The processor
has 12 KW of core as well, so I guess I could cut the bus down a bit more
for the purpose of debugging.

        Mode of failure is such:
        I powered up the shortened system and the front panel lights lit
[excitement]. Then I tried to examine some memory locations via the
panel, but when I hit HALT, the RUN light stayed lit. I tried every
combination of switches I thought was appropriate, but the RUN light
wouldn't go off. (Sounds like a simple bus error, really.) Upon
realizing that something was amiss, I decabled all the power connectors
from the logic and tested the voltages, which, surprisingly, were all
about 6%-9% above spec (and I'm not too sure that my VOM is accurate even
though it's analog). I didn't readjust the voltages, but reconnected the
power cables to the logic boards and retested the voltage levels. All
stayed about the same except for the -15VDC. It dropped to about 2V. Same
reading on both -15V regulators, by the way, and they seem to be connected
to different areas of the backplane, but I'm not sure. There seems to be
a high-pitch squeal (that sound of a laboring regulator) coming from
somewhere in the power supply cluster, but there's no smoke or crackling
sounds. I don't remember noticing the squeal with the power cables
disconnected, but that may be a subconscious hope and not a fact.

        So that's my predicament. I don't have much time to mess with
this beautiful old girl, so I hope someone here can increase my repairing
efficiency.

        Help me save this great piece of computing history. In return,
I'll at least give you an account on it if I get it to the point where
it'll run 2.9BSD or V7. I have SMD interfaces and disks, etc and
everything else I need (except a DELQA) to get it hooked up to the net.

Thank you in advance.

jake
Received on Wed May 26 1999 - 23:48:47 BST