DEC Backplane cleansing

From: Ethan Dicks <>
Date: Thu Dec 2 01:51:28 1999

The ongoing PDP-8/L restoration saga adds a new chapter. I was working on
a pair of them the other night and ran into an aggravating problem. The
area of the backplane around D-02 through D-15 that holds the M310 delay
line modules is giving me fits.

I have the power-restart option in and on. I turn a machine on and it runs
the lights in a random and pleasing fashion - the MA register shows some lights
brighter than others and the AC occasionally shows changes. After a few
seconds, the display gets more static - some of the lights in the MA get
brighter than they were; some get dimmer. This indicates to me that the
same region of memory is getting hit with a higher frequency. Now, here's
the annoying part: if I stroke the M310 cards, the display usually goes back
to a more random distribution of bits in the MA.

The M310 cards are instrumental in the timing flow of TTL -8s. I appear to
have a dirty backplane or loose backplane connector fingers. Without replacing
sections of the backplane (don't laugh - I have at least one new-in-the-box
p/N CAC-1 backplane section), how can I increase my connection reliability?
The card fingers don't show any visible corrosion; the gold looks intact. I
suspect the quality of the tin-plated steel in the backplane. Can say that
these are especially tight, either.

I'm not even as far as being able to reliably change and examine memory with
the frontpanel. Diagnostics are somewhat distant aids at this point. I'm
relegated to an oscilloscope and hand tools.

Any tips?



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Received on Thu Dec 02 1999 - 01:51:28 GMT

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