vax 780 uba problem

[Ron Stanonik]

A few weeks ago we began getting <DPPE> (data path parity error)
errors from our second unibus when trying to read tapes.  Since
the other equipment (dh's and an interlan card) on that unibus
didn't produce the errors, we suspected the tape controller.
Replacing the controller didn't cure the problem, so we
wondered if the tape drive itself might be producing faults
which manifested themselves as unibus errors.  After running
the tape drive on another machine without error, we began to wonder
if the unibus adaptor might really be at fault.  A little uba card
swapping and some diagnostics bore that out.

We still don't understand why the other devices didn't produce
the same <DPPE> errors, but maybe this will save someone some
effort.

Ron Stanonik
stanonik at nprdc.arpa