PDP-8/E PSU Debugging (was Q-bus pinout)

From: Chuck McManis <cmcmanis_at_mcmanis.com>
Date: Fri Apr 9 18:00:57 1999

At 07:09 PM 4/9/99 +0100, Tony Duell wrote:
>What's connected to what? In particular are there any cards in the second
>b/p and is it jumpered to the one that works? It could be that the +5V
>line is totally O/C and that 1.5V is coming via parasitic diodes,
>termination resistors, etc from logic lines.

Actually I did as suggested and unplugged the wiring harness that plugs
into the PSU and then the back plane. I put my DMM on the connector pins on
the PSU and the 5V line shows the same behaviour (higher value which
quickly drops to 1.5v)

I've got both jumpers pulled and all the cards in the front back plane and
the system runs (caveat some issues on the Front panel itself such as the
'STATUS' and 'STATE' displays aren't correct)

>Check the wiring in the PSU _and_ the wiring in the harness to the
>backplane. Take the backplane out if necessary.

The fault appears to be inside the PSU wiring harness somewhere.

>[Just to confirm : This is the linear PSU that mounts down the left side
>of the cabinet, right?]

Yes, and at this point it has been removed and is sitting on my test bench.
Access to the wiring harness is a pain in the fundament! This thing must
weight 75lbs all by itself. My current area of investigation is into some
of the crimp on connectors on the filter caps to see if perhaps they've
oxidized.

On another tack, the chassis I got did not come with any covers. I don't
know if this is "standard" or not. (I know the PDP-5 isn't designed to be
run outside of the rack its built into) The later 8's like the /f and /m in
the "mini" cases (one backplane) are covered when they are out of the rack
and so that has left me curious. I'm probably going to build a display rack
for it anyway with clear sides so that folks can "see" the innards without
risking getting fingers in them.

Thanks again Tony,
--Chuck

P.S. I'd like to thank Allison for relating the story of bringing up her
8/F since it inspired me to move forward on this project (code named
"FrankenEight" as it is a PDP-8 built out of parts exhumed from dead 8's or
other mysterious sources ...)
Received on Fri Apr 09 1999 - 18:00:57 BST