23 Nov
2019
23 Nov
'19
12:14 p.m.
From: Chris Zach
The MSV11-QC board ... failed startup diagnostics with
what looks like
a stuck bit. .. now I need engineering schematics for that board so I
can replace one of the 41256 memory chips. On the positive side it looks like
a pretty obvious stuck bit, just need to know which chip is at that
address and memory location....
I suspect you're out of luck on the prints, I think all there is is the
User Manual. Not to worry, it should be pretty easy to create a bit->chip
table, I did that for the MSV11-J:
https://gunkies.org/wiki/MSV11-J_QBUS_memory#Technical_information
when I needed to repair one; it should be pretty easy to duplicate the
process for the -Q.
I did it with a 2-instruction scope loop, doing a word write to a given
location, floating a '1' bit along a word of '0's, looking at the
'data in'
pin on the DRAM chips. I see the -Q has a 17x8 array of DRAMs, so 16 bits of
data and a parity bit (odd chip out); so in some ways even easier than the -J
(which had ECC). 8 banks, but with a little luck they're in some sort of
logical order.
I have a -QA, of the later etch rev, which is the same etch as your -QC;
so I can help with the mapping process, if you need it; let me know.
Noel