strange number corruption on pdp11/34

Noel Chiappa jnc at
Wed Jan 28 13:59:50 CST 2015

    > From: John Wilson

    > The *ability* to accept the FPP (and/or cache -- M8268 I think?)

Yup, M8268. 

    > And you need the right over-the-top connector (hazy memory says H882 or
    > H8822 for either or both option but I may have made those up).

There are two: if one has only an FPP (M8268) _or_ a cache (M8268) one needs
a single OTB connector, H8821 (they both go in the same slot, if one has only
one of the two). If one has _both_ the FPP _and_ cache, one needs a double
OTB connector, H8822. 

    > Better to reduce the variables and leave the FPP off for now.


    > From: Jacob Ritorto

    > I ended up ... mix-and-matching 8265 and 8266 boards from the old and
    > new sets to make a system that doesn't bus error and doesn't print
    > weird zeroes.

Let me make sure I get this. You have two M8265's, A and B, and two M8266's,
C and D. You're saying that _only_ the combination AC works; that AD, 
BC and BD all fail? In other words, only A and C work, and both B and D
are bad?

    > thank you all again for the insights and interest!

Hey, that's what we're here for!

    > If anyone is really interested in debugging these "bus error /
    > zero-inducing" cpu boards to find out what on earth was causing the
    > problem, I'd be happy to loan them out.

Nah, I've got enough of my own stuff to work on... :-) But if you decide
you have no use for dead cards, and want to sell/trade, please let me know!

    > Heck, I might even try to do what we were talking about initially and
    > write up some little math tests if you're really curious.

Well, I'm mildly curious, but _iff_ you want to repair them, you need to do
some of that, to try and figure out what the bug(s) are. (And of course
there's that busted M7265/M7266 set, too!) Since you have 3 sets, and only
one works, you might want to get a second set working before that set dies on
you, too... :-)


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