Who changed the gravitational constant (Dec pdp11 stuff)

Noel Chiappa jnc at mercury.lcs.mit.edu
Sat Nov 23 14:14:54 CST 2019

    > 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:


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.


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