PET 2001 oddity

From: mike_at_ambientdesign.com <(mike_at_ambientdesign.com)>
Date: Sat Jan 18 04:37:32 2003

At 18:18 17/01/03 +0000, Adrian Vickers wrote:
>So.... I figure the BASIC ROM has become slightly corrupted, OR I've got a
>flakey memory chip which reads OK but doesn't write properly. The question
>is, how to find out?
>1) Can the BASIC ROM be swapped with one from, say, a 3032 or 4016? In
>fact, which one IS the BASIC ROM?
>3) If, as my money is on, it's the BASIC ROM, can it be replaced with an
>EPROM - if so, there's a whole gamut of additional questions to follow....

Sorry, not knowing much about this machine in particular, can't suggest too
much, but...

>2) If it's a dodgy memory chip, what's the best way of isolating it? I have
>an oscilloscope, but nada skill in this sort of thing.

... at least perhaps you can rule out the RAM this way. Assuming memory is
socketed, what I'd do is swap it between two banks. Just take all the ICs
in one bank, and swap them with the another. If it's a memory fault, your
sypmtoms will change (probably quite a lot). If it's not a memory fault,
chances are the symptoms will remain the same.

This method depends on a couple of assumptions (that there's only one
faulty memory IC, for instance), but generally it's pretty safe to make
those assumptions, and it's saved me lots of time in the past.

The thought of trying to track down a RAM fault using an oscilloscope
sounds pretty scary to me, but perhaps there's a way of doing it.

For what it's worth though, this sounds more like a faulty BASIC ROM then a
RAM problem, as you suggest.

Mike.
Received on Sat Jan 18 2003 - 04:37:32 GMT