I'm trying to fix a memory problem in a IIe. The self-test reports one chip is bad with the message:
RAM 0 0 0 0 0 0 1 0
So I desoldered the chip in position 12 (second from the right in the row of RAM chips) and installed a socket. Continuity between the socket and where the traces lead (ground or the pins of other RAM chips) looks good.
The RAM chip I removed was an MT 4264-15. I bought some replacements off of eBay and installed one in the socket (with the notch in the correct orientation). The self-test reports the same error.
I found some alternative replacement chips, as I've heard that these Micron chips have a tendency to fail. I dropped in a Mitsubishi M5K4614NP-15, and it came back with the error again, and also when I tried an MN4164P 8-15.
Out of curiosity I tried the self-test without a chip in the socket, and it never completed. It also showed garbage characters on screen (different than the blocks usually shown when the self-test starts). So having *any* RAM chip in the socket at least allows it to complete the self-test (albeit fail it).
The PSU voltages look good.
I don't have another machine to test these RAM chips in, unfortunately. I tried multiple of the replacement Micron chips and they all did the same thing. So unless I'm having very bad luck and the half-dozen RAM chips I've tried are all bad, I think the problem lies elsewhere. I just don't know what else to try. Thoughts?