Re: plus/4 problems

From: Hársfalvi Levente (
Date: 2001-12-13 14:05:17


Daniele Gratteri wrote:
> A person has contacted me for asking a question about the strange behaviour
> of his plus/4.
> He said that it works for a few minutes, then it shows random characters on
> the screen and finally it doesn't accept keyboard input anymore.
> I said him the problem can be the 7501/8501 CPU since, if I correctly
> remember, is it that makes the keyboard to work. Can it be the source of
> this problem? Ciao!

From the above, I'd better suspect the RAM chips or the TED. From the
garbage on the screen, I'd say it is a RAM problem (and since a RAM
problem can also cause problems for the system program (by losing system
variables), it could be as well the cause of unability to enter
characters from the keyboard).

If he told you what characters he actually sees when it starts to get
rubbish, we could probably predict which data bit is stored wrong (or
which is destroyed).

BTW, once I had bad RAM multiplexers in my C-16, and the problem caused
similar garbage effects (though, the computer was not able to start

No, the keyboard is handled by the TED chip (plus a very stable, I'd say
never defect 6529B).

Best regards,


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