PDP-8/I memory problem

From: O. Sharp <ohh_at_drizzle.com>
Date: Wed Nov 5 19:33:48 2003

> Bring on the esoteric guesses! :-)

Damn! Pick an easy problem next time. :)

-Is there continuity between the sense-amp MEM00 outputs (A31, pin A1;
A17, pin A1) and the MEM00 input to the major register gating (F34, pin
R1)? Seems obvious, but I'll ask.

-If you physically remove one of the 4K core stacks, including the sense
amps and inhibit drivers, does the problem go away? If so, then it's
possible one of its sense-amps has gone berserk and is forcing the signal
low for everybody. Seems hysterically unlikely, but I'll suggest it.
Similarly I suppose a defective inhibit driver might _some_how do the
same thing to the original input, though it seems less likely.

-If you took the MEM00 line coming from the sense amps and tied it high,
say perhaps at its entry to the major register gating (F34, pin R1),
and then tried a few EXAMs, does the MB00 finally get pulled high? It
better. :) If it doesn't then something must be happening with the
major registers and/or gating, M220 swaps notwithstanding. Maybe a
bad contact at the backplane?...

-If you take the MB00 line, disconnected it from the M220 (E34, pin U2)
and tied it high, then took MB00(1) off E34 pin T2 and tied it to ground,
it should force the writing of a 1 at that bit no matter what the hell
may be happening elsewhere. Does it? If not, what happens if you reattach
those and then force MCBMB00 high instead (B12, pin E1)? Hopefully one of
these might provoke a reaction, and thus narrow down the problem to
something prior to the inhibit drivers themselves. If so, great; if not,
a similar process might be tried from the sense-amp outputs forward
(though there's not nearly as much to test in that direction).

...I hope one of these ideas makes an answer appear.

You know, the twisted thing about this process is that I'm actually
enjoying it. But I suspect most of you will understand that. :)

                   -O.-
Received on Wed Nov 05 2003 - 19:33:48 GMT