Sigh. Bringing up a PDP-8/M

From: Chuck McManis <cmcmanis_at_mcmanis.com>
Date: Tue Apr 13 18:56:24 1999

At 06:41 PM 4/13/99 +0100, Tony Duell wrote:
>Hey, that's another reason _not_ to do board-swapping ;-)

DEC FSE jokes aside, how else might you bring up a random collection of
boards? My strategy was this:
         1.) Debug the chassis.
         2.) Install components from a working 8/M.
         3.) Replace componets from the working 8/M with questionable
             components.
        3a.) If the replaced component failed: Fix it.
        3b.) If the replaced component worked: Move to the next one.

>OK... First thing is to clean out the backplane in the 8/m. Use a vacuum
>cleaner to remove loose dust and then squirt isopropyl alcohol
>(propan-2-ol) into the connectors.

I've done that, although that foam is damn sticky. (Twice I've debugged
problems which consisted of plugging in the "defective card" scoping it,
removing it, noticing another bit of gunk on the fingers, cleaning the
fingers and the slot again, inserting the card and having it work.

>Then assemble a minimal system. IIRC you don't even need memory. Just the
>clock/timing card, the 2 CPU cards and the bus loads.

It is a minimal system :-) Actually I could remove the core stack and run
just the CPU and loads, I'll do this tonight.

>Then, if it still doesn't halt, check the power supply. I can't remember
>what the power good line will make the CPU do if it's in the wrong state,
>but I don't think it forces the CPU to the RUN state (unlike the 11/45...)

Power supply is good, its the first thing I checked [switcher type B]
(4.96v and -15.01v and +14.99v) with the minimal system installed.

BTW, the "best" tool I've found for working on PDP-8s is the Radio Shack
scope probe. Its more than fast enough to look at the signals. I suspect a
Logic Dart would be better but I've not had enough funds for that toy yet.

--Chuck
Received on Tue Apr 13 1999 - 18:56:24 BST