General Question about UNIBUS backplanes

Noel Chiappa jnc at
Tue May 24 06:49:11 CDT 2016

    > From: Bill Degnan

    > I removed the core backplanes and returned the DD11-C to the orig
    > config next to the CPU. I re-inserted cards as-was. I am not getting
    > comms from the M7856.

Ugh. Not good. Does it respond on the UNIBUS? (I.e. if you try to read
the registers from the front panel?)

    > I may have shorted the card.

If you somehow plugged it into one of the core backplanes, good chance, alas.
They have either -15V or +20V (I think the latter, for the MM11-U) running
around on various pins.

(Oh, BTW, you probably already know this, but just in case not: those
backplanes take specific boards in specific slots; check the manuals/prints
for the correct slots.)

Do you have a spare M7856 you can swap in to make sure the machine is
otherwise functional? If not, let me know, I have a bunch of spare M7800's,
I can send you one (known, tested good).


More information about the cctalk mailing list