5 Nov
2003
5 Nov
'03
5:10 a.m.
O. Sharp sez...
Somehow I missed Robert Krten's original post, but I saw two lines
quoted, and since minimum-information puzzles are fun I'll quote it for
reply. Forgive me if I'm missing obvious clues that were presented in
the original. :)
Yup, both core stacks the same...
> If I deposit 7777, I can examine and get
3777. This machine has 8k of
> core, and the problem is the same in both 4k banks.
In _both_ core stacks? Well, there goes the obvious inhibit-driver
answer... If it were me, I'd be tempted to stick a probe
onto the output of
the MB00 flip-flop (M220, E/F 34, pin U2 of the E side) and see if it
were spitting out usable information or nonsense. If it's nonsense,
you've probably found your culprit. If it's being sensible, I'd follow
the signal to the inhibit drivers (and perhaps to the front panel as
well) to verify it's going where it needs to go.
I've swapped the M220 cards; plus the MB output goes to the front panel,
and it looks good on the front panel when I deposit.
(Does that signal go to the inhibit drivers directly?
It may go to the
memory extension control and get rebuffered there first, but alas I
don't have my extended-memory-control drawings handy... If the MB00
signal _does_ get rebuffered between the original F/F and the inhibit
drivers, that rebuffering device would be an even more likely place to
look for a problem.)
Nope; looks like it goes direct to the drivers. I also checked the
line coming back the other way, and it goes direct into the M220 card.
Let me know if this helps. I'm curious now.
[I suppose it's possible that the bit 0 inhibit drivers of _both_
stacks could independently be locking themselves on, but it seems
unlikely. :) ]
Swapped inhibit drivers with "known good ones", and the problem persisted
the same way...
[I suppose your MB00 panel light could have burned
itself out at an
inconvenient moment as well, but that seems entirely too simplistic an
answer. :) :) ]
Nope; panel light works :-)
Cheers,
-RK
--
Robert Krten, PARSE Software Devices +1 613 599 8316.
Realtime Systems Architecture, Consulting and Training at www.parse.com
Looking for Digital Equipment Corp. PDP-1 through PDP-15 minicomputers!