Argh!!! PDP-8/m Memory

From: Zane H. Healy <>
Date: Sun Nov 21 13:52:06 1999

>[PDP8/m with core problems]
>> The first thing to check is that all the top connectors are in fact on.
>> There should be no "edge" connectors visibla at the top.
>In the core memory set, sure (you need 4 top connectors here -- 2 to link
>to the core stack to each of the other 2 boards). But there will be open

That was kind of obvious, and thanks to a pretty good picture in the
maintenance manual I was able to verify how I was supposed to have
connector blocks on stuff in the system. Thankfully I had all of them.

>edge connectors on the top of the CPU set -- you can insert the EAE card
>set between the CPU boards and the clock generators, and it has top
>connectors to both the CPU and the clock.
>IIRC, without the EAE, there's nothing on the top connectors of the M8330
>clock, and 1 top connector between the 2 CPU boards (maybe 2 -- whereever
>there are 2 connectors aligned on the 2 CPU boards).

Looks like the EAE would have one connector to the Clock, and one to the
CPU board set.

>Worth cleaning the top connectors as well...

I cleaned them, but it might not have been good enough. I ended up using
rubbing alcohol to clean all the contacts on the boards.

>> Been looking through the maintenance manual, and it looks like among the
>> things I need to do tomorrow to check this out is to test voltages on both
>> the G104 and G227 boards. This has me wondering, does it matter if the
>Do you have a 'scope? This is the sort of problem where I'd start by
>checking a few waveforms. Check to see if the CPU appears to be writing
>data to memory. Check to see what the address decoder and XY drivers are

Well, I've got what a friend tells me is a pretty good Tek scope, and no,
he didn't sell it to me :^) However, I don't know that the probes are
really usable for computer equipment (the two with it look homemade, and
the Tek probe I scavanged about 20 years ago either from the dumpster
outside the Tek Country store, or the store itself).

Then there is the embarassing part, I still haven't figured out how to use
a scope...

I'm sure I can pretty much figure it out without to much difficulty, just
concerned about the probes. Been meaning to get a decent set, but...


| Zane H. Healy | UNIX Systems Adminstrator |
| (primary) | Linux Enthusiast |
| (alternate) | Classic Computer Collector |
| Empire of the Petal Throne and Traveller Role Playing, |
| and Zane's Computer Museum. |
| |
Received on Sun Nov 21 1999 - 13:52:06 GMT

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