20 Jan
2019
20 Jan
'19
1:48 p.m.
On Jan 20, 2019, at 3:56 PM, Fritz Mueller via cctalk
<cctalk at classiccmp.org> wrote:
...
I'm technically curious, now, about the failure modes of these sorts of DRAMS. I
guess in addition to stuck bits, there are also potential decode fails (show up on address
test, but not ones/zeros) and some errors that have history-dependence, perhaps internal
latches (show up on random data test, but not address or ones/zeros.) I'd guess also
there might be potential for crosstalk, noise, and "fading bit" type issues as
well? Will have to see after I make the next round of repairs if there are still
additional problems that the MAINDEC flags that my simplistic diag isn't shaking out.
There are tests for crosstalk and decode problems, they may be marked as core memory tests
but they might work anyway. There is the "no duplicate address test" which
verifies that each word is accessed by exactly one address value. That would catch decode
issues -- for example, a stuck address bit or a stuck decoder would be caught quickly.
Not quite crosstalk, but there is the famous "core heating test" which hammers
on a specific set of addresses which are near each other in the core mat, to see if the
heat generated by those rapid accesses in a small physical area cause trouble.
paul