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. :)
>
> > > 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...
Yup, both core stacks the same...
> 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!
Received on Wed Nov 05 2003 - 13:10:19 GMT