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Posted By

crock
on 2014-03-29
07:56:23
 Re: Suspected PLUS/4 Ram fault

Hi there Imperious, what is the background colour of the screen, can you take a screenshot? If you've already tried the RAM there's another couple of things which could cause the same symptom, including the multiplexers (74LS257's) or a ROM holding one of the datalines high or low.

If you've programmed a kernal version of Diag264, try taking all the other ROM's out, but not the PLA (251641-02), as this is necessary for the machine to run. I have never seen a flaky CPU or TED create that symptom, but it is possible. If you have a working machine, do some chip swapping to prove all the removable chips are good.

Rob



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