21 Sep
2011
21 Sep
'11
10:41 a.m.
Yes, the drive was working just fine. I think this is
an electronics fault
on said card. Whatever I do I can observe changes on the DIFF outputs from
the ROM (outputs M0 to M4) but not on output M5. And the problem is that I
don't know when this output should go low.
A more general hint :
While individual bits of these bipolar PROMs can fail (in either
direction -- the fuses can 'grow back'), it's less common than failures
with the other circuitry in the device.
If you don't mind desoldering the ROM and reading it out, it's worth
checking for :
Stuck data bits (a data line which is 0 or 1 in all locations). If that
pin is conencted to other circuitry, it's a fair bet that it should
change sometimes
Address liens that do nothing. If the first half of the dump is the same
as the secodn ahlf, thena the MSB address inptu is not doign anything, if
the first had second quarters and the 3rd and 4th quarters are the same,
then the next addres line isn't doing anything, etc. If the address line
is driven by other circuity, it's a fair bet it should ahve some effect on
the output.
IF the dump apsses those 2 tests, it's quite likely the ROM is OK.
-tony