strange number corruption on pdp11/34 - test-drb@ccmp.vtda.org

28 Jan 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. 
Indeed!
...
  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... :-)
        Noel