PET 2001 oddity

From: Ethan Dicks <>
Date: Sat Jan 18 00:38:00 2003

--- Adrian Vickers <> wrote:
> I dug the 2001 out of the cupboard the other day...

Can you give more information about *which* 2001 you have? There
are at least two major motherboard revisions for the static-RAM PETs.
They use different ROMs and RAMs.

Also, as I have one, there are also models of 2001 that have _dynamic_
RAMs. My 2001-N has 32K worth of 4116 chips (from the factory) and a
full-sized graphic keyboard. If it were for sale in Europe, it would
most likely been labelled a 3032, for comparison, but here in the States,
it says "2001" on the front.

I bring it up because I _think_ you are talking about the original
chicklet-keyboard SRAM PET, but you didn't come right out and say so.
> Unfortunately, the PET seems to have developed an odd fault: It won't
> take a BASIC program, and some keywords seem to be knackered...
> So.... I figure the BASIC ROM has become slightly corrupted, OR I've got
> a flakey memory chip...
> 1) Can the BASIC ROM be swapped with one from, say, a 3032 or 4016?

Most likely not. If your 2001 has 2114 SRAMs, perhaps. There are
upgrade ROMs (BASIC 2.0, anyway) _for_ the 2001

> In fact, which one IS the BASIC ROM?

BASIC lives in several ROMs, the Kernel lives in several ROMs. BASICs
prior to 4.0 occupied $C000-$DFFF, and the Kernel occupied $E000-$FFFF,
minus the PIAs and VIAs, etc., at $E800. BASIC 4.0 starts at $B000
to add room for diskette commands.

In my PET, $9000, $A000 and $B000 are filled with user-supplied firmware
(better machine-language monitor, BASIC extensions and a tape speeder).
These sorts of things, plus ROMs for word processors and other applications
were somewhat typical amongst serious PET users. Dunno if yours has
anything like that, but if you find ROMs where you expect none to be,
that's probably why.

> 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.

The typical way of testing RAMs in a C= service center was to rotate
a pair of them from bank to bank and see if the symptoms shift. It
was especially handy for detecting zero page problems.

Not sure how you'd use an oscilloscope to detect transient memory
errors not caused by design problems (like an undershoot problem).
A logic analyzer might help... you could set it up to trigger when
things don't happen when you expect, for example.

> 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....

Yes, with the caveat that you might not find an EPROM with an exact
pinout to match the masked programmed ROMs you'd be removing. In the
case of _my_ 2001-N, it takes 2332 masked programmed ROMs, or 2532
EPROMs, *not* 2732 EPROMs. If your board is older, I do not know
what parts exist that would drop in place. You can make/buy ROM
pin swabbers to use any 2K or 4K EPROM in that socket.

There is also a fellow on the cbm-hackers list who has a board
that plugs into the CPU socket and provides a full boat of RAM
and ROM. Very handy for sweeping away problems with 8K static
PETs. Might even be cheaper than a box full of pin swabbers.

Now... I _have_ seen RAM and ROM chip fail in PETs. What is much
more likely, however, is to have those cheap-ass crappy sockets
oxidize. Reseating and/or removing and reinstalling all the socketed
parts is the first order of business. Check the pins of all the
ICs you remove. Some chips from that vintage have enough silver
in the plating to tarnish to black. Check the classiccmp archives
for the "best" way to remove it. Be sure not to bend any pins
while you are at it (easier than you might think - just fixed
another machine where a corner pin was folded under and looked OK
from 2 angles)

So... if you are attempting to do a minimal repair that also looks
much like the original, you might have to resort to pin swabbers
if it's a flakey ROM chip. If you just want it to work and aren't
hung up on "original" parts, you might want to contemplate a
complete ROM/RAM transplant. ISTR the boards are around $35USD,
but that's only a ballpark estimate.

Good luck,


P.S. - if you don't know about it's a
great site with schematics and firmware.

> Thanks in advance!
> --
> Cheers, Ade.
> Be where it's at, B-Racing!

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Received on Sat Jan 18 2003 - 00:38:00 GMT

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