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Old 18 July 2019, 00:45   #1
Vypr
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Location: East Kilbride, Scotland
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Help identifying Faulty RAM chip.

I have two RAM boards for my A2000, both faulty.
One is a A2052 whicch had pretty much all the RAM chips fried, they have all been replaced but still getting errors above the 512Kb range, I'm currently waiting on new decoupling capacitors to arrive as I'm pretty sure I damaged a lot of them desoldering the RAM chips so that board has been put to the side fo rnow.

While waiting for the parts I managed to get hold of an A2058 board which just has the initial 2Mb onboard, it detects OK but when I run memory tests it fails.

Systest returns the following error:



Code:
ERRORS:      D31..D24  D23..D16    D15...D8  D7....D0
(X=ERROR)     76543210   76543210     76543210  76543210
32-bit bus    --------   -----X--     --------  -----X--
16-bit bus                             -------- -----X--
I have also run MBRTEST-2 which results in the following errors:

MSCAN test
Wrote 5555 Read 5551

RSCAN test
Wrote aaaa Read aaea

I'm guessing it is the chip at U51 that is the problem but the MBRTEST results are confusing me a little as from what I can gather, the chip is returnign High when it should be Low and vice versa

has anyone ran into anything similar that could point me in the right direction?
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Old 18 July 2019, 17:30   #2
Daedalus
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Hmmm, I would suspect U52 since that's the chip corresponding with bit 2 as far as I can see from the schematic. that might explain the confusion, but I would also check that U2 is working correctly, since this is buffering bit 2 and could also be causing that bit to fail.
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