PETS & the Silly Game

From: Doug Spence <ds_spenc_at_alcor.concordia.ca>
Date: Thu Apr 24 06:38:21 1997

On Mon, 21 Apr 1997, Larry Anderson & Diane Hare wrote:

> I know pretty much PET software & usage, and have a bunch of good books
> to help me on other aspects... ;)

There used to be a copy of Osborne's "PET/CBM Personal Computer Guide"
around here someplace, but I suspect my brother took it with him when he
moved out, even though he's a C64 man. (Darn!) I really need to find a
good shop with old computer books in it. All of the second-hand
bookstores I've been to specifically state that they don't keep computer
books or magazines older than 5 years (or so) old. :/

> Never heard of that, but I did have a friend who tried expanding PET
> memory by piggybacking RAM chips ; that fried his... (beware, he's
> still out there...)

Interesting. I performed the piggyback RAM hack on my Amiga 1000 (back
when it was worth real money) and that seems to still be holding up. I
*don't* want to do that to my PET, though. :) (In fact, in retrospect, I
wish I hadn't done it to my Amiga, either - I should've bought an Insider
board instead and keept the Amiga in its original condition. I wasn't a
collector yet, though. :) )
 
> > Anyway, is it still possible to get 6550s anywhere? And if not, is there
> > a replacement that could be used?
>
> MOS technologies found out they wern't good RAM manufacturers, the
> comptible and available chip number you seek is 2114. Which I have
> found in a Jameco Catalog (415-592-8097)

OK, cool. I'm actually need some 2114s for repairs to a VIC-20 3K
Expander cartridge, too, so I can just buy more of them when I actually
get myself to a place that sells them.

BTW: Who here thinks I'm crazy for wanting to run an "old-time BBS" off a
VIC-20? Who here thinks it's impossible? :)

> Wow! An MTU sound board! Got to hear a demonstration of it some 15
> years ago, pretty nice sound! One of these days I might come across one
> of 'em for my own.

The local high school had three PETs with these sound boards, and this is
one of them. (Curiously, at the time, the "Computer Science" department of
the same high school only had a single TRS-80 Model I and an Altair 8800.)
The music teacher wrote software to teach scales and chords, in BASIC,
based on the Cursor #4 tape's cover program. I found copies of these
things in my brother's cassette collection (I was still in elementary
school at the time the PETs were in use).

The sound generated by the board *is* nice. I had an online friend over
during the holidays, who collects old synthesizers, and he was quite
impressed with the thing. Too bad I couldn't find the cassette with the
professional music software on it (I forget what it's called) that lets
you compose the music on the staff on the screen, and that scrolls the
music as it plays. It's really impressive for an 8K machine!

> Back to RAM, from the next paragraph I would say that you can add via
> that expansion
> board. But just in case I'm mistaken, here is something I found in
> Nick Hampshire's
> PET Revealed:
>
> ... The old 8K machines used 4K bit static RAMs, these were one of two
> types the 6550 and the 2114. Both these chips are functionally
> indentical in most respects since they are organised as 1K by 4 bits.
> The latest versions of the static RAM 8K machines used the 6550....

Interesting that he says the latest versions of the 8K machines use the
6550... It's possible the old 8K here with the miniature multicoloured
keyboard (love that thing!) had its RAM replaced at some point. It was,
after all, an abused school machine, and the lid wasn't screwed down. (The
sockets in that particular machine are so bad there's no point in screwing
the lid down! Having to re-seat chips is a regular occurrence.)

> ... The new 32K and 16K dynamic RAM machines use the 4116 memory chip
> and the dynamic 8K the 4108. These two RAM chips are pin compatable,
> with the 4116 having 16K bits of memory and the 4108 8K bits. This is
> useful since it allows the same circuit board to be used for all sizes
> of machine. Memory on the 16 and 32K machines is organised as two banks
> each of 16K bytes, only one bank being implemented in the 16K....

So I guess Commodore stopped drilling holes in motherboards to prevent
upgrade? :)

I was hoping these numbers would match something on that expansion board,
but they don't. :/

The majority of the non-MOSTEK chips that appear to be memory chips, are
marked with MM5298J-4A, one is MM5290J-3, another is MM5290N-3... oops! I
take the last paragraph back! One of the non-gold-plated MOSTEK chips is
a 4116! We have identification! :)

Assuming all these chips are the same, this was a 16K RAM board. This'd
be nice to get running.

> Sounds like an Expandamem or ExpandaPET to me, I have the docs for it, I
> think it has schematics and stuff. Mine have the same chips too, look
> like tiny ROMs or EPROMs..

Yeah, those chips are bizarre.

> > The board is dead, BTW. The PET won't operate with the board plugged in.
> > It just comes up with a screenful of garbage characters.
> [clip]
> > Both connectors on the cable that leads from the expansion board to the
> > motherboard are noticeably burnt. In both cases, the burn marks surround
> > the pin that connects to the black wire.
>
> OUCH!!!! That's gotta hurt... Hope you figure out what did that.

I doubt I will. Presumably it was caused by some kind of accident, not
through some fault in the PET, because the PET the board came in has been
running for a couple of years (with the other PET's RAM in it) and hasn't
experienced any problems. The memory board, though, is of course quite
suspect. Perhaps I should replace those capacitors and regulators before
I replace the RAM and try to fire it up again? (How would one test a
capacitor to see if it's OK?)

> > The only identifying mark on the board is the text:
> > R 3014
> > rev.
> > C
> > COPYRIGHT 1978 R.C.Factor
>
> My ExpandaPET book has (c) 1979 Computhink (yours could be an earlier
> version?), also my board has four breadboard (edgecard) sockets to add
> devices like disk drive controller cards and the like.

There aren't any extra connectors on my board. The only connectors are
for power in, power out, and the one that plugs into the side expansion
connector.

> The only other thing I could think of it being (if it had a patch into
> the monitor connector) would be a Visible Memory (hi-res graphics)
> board. But I doubt that.

Oooh... I wish. :) I didn't think you could even get such a thing for a
2001, I thought graphics boards were the domain of the 8032 and like
systems. No idea why I'd think there'd be such limitations on one PET and
not on another, though. :)

> Let me know If you want a copy of the documentation I have for my board
> to see if it will help.

I'll pass on that (for now, anyway) as it seems to be a simple RAM board.
If I replace all the parts, it should work, and presumable there's nothing
I'd really have to know about to use it. :)

BTW, there's also another piece of bizarre PET expansion around the house
somewhere... Another 16K of expansion, actually. That's what those large
music files were created with. But the thing is HUGE and it consists of
exposed circuit boards, so I didn't particularly want to use it in its
current state.

This memory expansion has its own power supply. The cable from the
expansion connector on the side of the PET goes to the top edge of a large
board that is in turn plugged into a socket on a long expansion bus type
of thing (with the Vector Graphics label on it). There is another board
of equal size to the first also plugged into this expansion bus, right
beside it. There are only the two sockets on the long PCB of the
expansion bus, but it'd be easy to add more sockets. I should dig this
thing out to see if there's anything else interesting to say about it.

Seems like an awful lot of space for 16K. My little internal board would
be much nicer.

This strange contraption wouldn't be some kind of interface between the
PET and an S100 bus, would it? (THAT would be cool!) How would I know an
S100 bus if I saw one? :)

> Larry Anderson
>
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Doug Spence
ds_spenc_at_alcor.concordia.ca
Received on Thu Apr 24 1997 - 06:38:21 BST

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