21 Apr
1997
21 Apr
'97
2:23 p.m.
Date: Sun, 20 Apr 1997 07:21:01 -0400 (EDT)
From: Doug Spence <ds_spenc(a)alcor.concordia.ca>
To: classiccmp(a)u.washington.edu
Subject: PET stuff
Does anyone out there know much about the old PET 2001
machines?
I know pretty much PET software & usage, and have a bunch of good books
to help me on other aspects... ;)
I received a PET a couple of years ago, in which all
of the 6550 SRAMs
were fried. I replaced them with the chips from another PET 2001 (one
with the miniature keyboard, from 1977) and the system worked fine.
Does anyone know how all of the memory chips could've been killed?
I tried them in various patterns in the sockets, and it does seem as if
all 16 of them are fried.
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...)
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)
Even better: Can I simply replace the 6550s with
another type of chip and
get more RAM in the system? Most of my software works in 8K, but I do
have some music files that require more. (I have one of those external
music boards that plugs into the cassette2 and user ports, that delivers
four voices.)
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.
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....
... 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....
Now, another question. With that same PET, came an
expansion board of
some kind. Its like a daughterboard, physically mounted on posts above
the motherboard, but connected via the memory expansion connector on the
side.
It appears (yes) to be a memory board, with 16 RAM chips on it. At least,
they look like they could be RAM chips, judging by the traces on the
board. However, I've never seen RAM chips with gold contacts and gold
plates on their backs before, as six of these chips have, so I'm wondering
if this could be more than just a memory board.
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..
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.
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.
Does anyone have any better guesses than me as to its
function? (Can the
edge connector on the side of the PET be used for anything other than RAM
expansion?)
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.
Let me know If you want a copy of the documentation I have for my board
to see if it will help.
Doug Spence
ds_spenc(a)alcor.concordia.ca
------------------------------
What I bought: Atari 1200 XL, 1050 Disk Drive, and Supra Atari 300 baud
modem (all sans power supplies *sigh*) for $15 at a flea market (need
power supplies to test them still), and a (working!) Apple ImageWriter
II for $14.95 at a thrift shop. Software.
What I passed up:
2 CoCo 3s (bare), one for $15 one unknown
1 CoCo dual 5.25" Disk Drive price unknown
1 black/silver TI 99/4a (bare) $10
1 Atari 800 (bare, but had BASIC cart inside) $10
Plus/4, C-64, an MPS 801, tons of IBM clones didn't bother pricing.
Oh! Last week I happend upon a Panasonic MSX unit! Looked
interesting, unfortunately the guy couldn't sell it cause 'they haven't
decided how much to price it' (hence it would probably be expensive),
sure looked neat, had alot of I/O and noted a switch to change tape baud
rates. (they had the tape program/books already out on the floor just
waiting for kids to tear them apart.)
Larry Anderson
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On Thu, 17 Apr 1997, Sam Ismail wrote:
> Hey, let's have a contest. Let's see who can score the best lot of
> classic computers this weekend. We can score each other based on the
> type and age of the computers/software/accessories we got, then tally up
> the points and whoever has the highest score gets a pat on the back.