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. -- ------------------------------------ personal: http://www.cameronkaiser.com/ -- Cameron Kaiser * Floodgap Systems * www.floodgap.com * [email protected] -- Not sun-worshippers: Son-worshippers! -- Uhura, Star Trek "Bread & Circuses"
