Tired memory?

Noel Chiappa jnc at mercury.lcs.mit.edu
Tue Aug 18 08:04:32 CDT 2015

So I've seen an odd phenomenon on some older QBUS memory boards I've got in.
I can't understand it, and I'm wondering if anyone else has i) seen it, or ii)
understand the cause.

What happens is that the _first_ time I plug them in, some don't work - some
(maybe all, sometimes) locations are mangling the data (I forget whether it's
dropped or picked bits). Oh, and we're talking 4164's/41256's (or equivalents)
here, for the actual devices.

However, if I let them sit for a bit (powered off), and then try again, they
work fine!

I first experienced this phenomenon on some M8044's, which have on-board
electrolytic filter caps, so I was guessing it was caused by some sort of
noise caused by the caps not working, and after a little while powered on, the
caps reformed, and things started to work.

However, I just experienced the same phenomenon on a Clearpoint DCME/Q4E board
- which doesn't have any electrolytic caps on it. So that can't be it.

Anyone have any clue what's going on?

(Oh, and of course, for others - if you buy and old memory board, and it
doesn't work... don't immediately put it in the 'bad' pile, wait a bit, and
try again. You might be seeing this.)


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