Backup Ram Error


Zero's Secretary
Hi Guys,

I have had this 4 slot board in storage for a while now since I never had the patience to fix it until now. I am getting this error:

Anyone has any idea what ram chip could be causing this?

I have searched around but I have not found anyone with the same exact error.



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Mickey's Coach
I don't know for this board off the top of my head, but the RAM configuration is two ICs representing the upper and lower 8 bits to form a 16 bit word. This looks like bit 4 (out of 0-7) is stuck low, likely a bad trace, on the backup RAM that is for the lower 8 bits. It's possible the RAM is actually bad, but this probably a trace issue given that it's in the backup RAM.


Thou Shalt Not, Question Rot.,
I'd check the continuity on all the traces of the ram and also look for corrosion.

When you get a READ 55xx (where x=any number), then the problem is related to the "lower" ram, that is the ram whose data lines (D0-D7) are connected to D0-D7 of the CPU. When you get a READ xx55, the problem is the "higher" ram, with data lines connected to D8-D15 of the CPU. Check Nightmare Tony's many and very useful posts on the subject.


Edo Express Delivery Guy
It could also be a bad IC controlling the read/write mode of the RAMs (74HC32). I had that issue on my MV-1FZ board, IC17 was faulty.