PDP-8/E EAE Troubleshooting

Kyle Owen kylevowen at gmail.com
Thu Mar 19 23:48:18 CDT 2015

I've recently been in the midst of repairing an EAE set for the Omnibus. I
finally got it working tonight. Surprisingly, unless I was simply reading
it wrong, it appears as though the M8340 etch rev. D is in fact compatible
with M8341 etch rev. D, despite what the DEC ECO Log suggests. Now, on the
other hand, the M8340 does have some ECO changes, but some of these are not
cited in the log, perhaps indicating that it was brought up to an
equivalent revision E or F, but there are still some big differences
particularly involving the inputs to the instruction register.

Anyways, here's an album: http://imgur.com/a/QVRLs

The TL;DR of it all is I replaced one bad IC. I also ended up making a
board that replaces the hard-to-find Signetics N8235 with easy-to-find
7400-series components.

A big thanks to all those involved (you know who you are!) in helping get
this set functional again, just in time for VCF East and Southeast!


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