7 Dec
2014
7 Dec
'14
12:14 p.m.
On 12/07/2014 07:22 AM, Noel Chiappa wrote:
Hi, all, I'm trying to fix a broken MSV11-L card
(M8059-KF). The symptom is
that it always reads back with the 020 bit set, but otherwise appears to be
fine. (E.g. you can write a number in 0, and a different number in 020, and
each reads back OK, with the exception that the 020 bit in each is always
set; i.e. the addressing is working fine, as is the QBUS generally.)
So poking around with my 'scope, I find that the latched D04 signal ("LAT D04
H") is always around 2V - not good! From the prints:
Power the system off for 10 minutes, then power on and read
various locations.
If data bit 4 shows 1's and 0's, then the reading is OK, and
it is the writing path
that is stuck. I think this may be the case, as you say the
bit is stuck when you
scope it, I assume when writing to the memory. That may
narrow down which
chip is the culprit.
Jon