pdp11/45

From: Sipke de Wal <sipke_at_wxs.nl>
Date: Sat May 29 22:31:07 1999

Use de squeal and boardwsapping (or even an empty backplane) as an
indicator of where the problem is. -12V is not used everywhere on the
system so you may be able to narrow it down a bit.

Sipke de Wal

Jacob Ritorto wrote:
>
> 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 Sat May 29 1999 - 22:31:07 BST