[SiriusHardware]

Down the right hand side of the test display are the figures D0 to D7 (Data lines D0 to D7) so it looks like the test is indicating a RAM-wide problem with RAM data bits D1, D4 and D7. We know that read access from the system RAM is through the buffer IC, IC50, 74LS244, but we also know that read access from the ROM is through the same buffer, so that would suggest that the system should be able to read from the DRAM through that buffer OK as well.

Data written to the RAMs is supplied to them from the main data bus buffers which have already been replaced.

With the RAM TEST eprom running can you scope the following pins on ALL of the RAM chips

In the following group, the signal on each IC should look broadly the same as the signal on the same pin on all the other ICs, so what you are looking for is an odd man out, one or several where the signal does not look like the signal on the same pin on the other chips.

-Pin 3 (WE
-pin 4 (RAS)
-pin 15 (CAS)
-pin 13 (CS)

In this next group the signals on the lines are very complex because data coming from the RAM is mixed in with code being read from the ROM. The waveforms themselves will not be regular but going up and down in seemingly random fashion.

Scope IC50 pins:-
2
17 (?)
4
15
6 (?)
13
8
11 (?)

In particular, we are looking for any significant visual difference between the signals on the pins I have put a question mark next to, and the others. If you want to post pictures that will be helpful but make sure all photos are taken with the Time / Div control at the same setting.

Edit: Do what Mark said first.