3 Jul
2023
3 Jul
'23
6:56 p.m.
Answering my own question for posterity:
However, test 1, the RAM test, should show long
flashes of the green LED if RAM
is bad. I was prepared to see all long flashes which might implicate the
buffers or address decoder, but instead it won't blink the LED at all in that
or any of the other tests. The red LED remains lit and appropriately
extinguishes when the RS button is down.
Again, the board works correctly and fully certifies the other two KIMs.
What would cause it to hang (?) in the RAM test on the defective one?
Dwight suggested something wrong with the address lines. That made sense, since
the continuity problems I had on the board were on the address lines (turned
out to be lifted traces). However, after spending a couple hours more with the
tester, the actual problem was two address lines that had an intermittent
short. I cleaned that up and everything passes.
The original fault, a bad 2nd bit from $280 to $2bf, was indeed a single RAM
chip gone bad in a single row. Now that it's replaced and the board is fixed,
the fault is gone. Buffers and address decoding check out just fine.
--
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Cameron Kaiser * Floodgap Systems * www.floodgap.com * ckaiser(a)floodgap.com
-- Not sun-worshippers: Son-worshippers! -- Uhura, Star Trek "Bread &
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