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From: [e-mail] (IBRanhdohm)
Newsgroups: comp.sys.cbm
Subject: Vic20: interesting cartridge found
Date: 2 Feb 1996 07:50:07 -0500
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Hi folks!

I apologize in advance for the length of this. However, some of you might
like it; I hope so. I'd like to get some response on this, and see if
outside opinions confirm what I've guessed.

I found an odd cartridge recently in my collecting travels. See what you
think about it....

This particular Vic20 cartridge is #1938, called "Tooth Invaders." I've
seen and bought plenty of Vic20 carts, but this one is very different in a
number of ways, as I'll explain. The game itself is common enough to the
Vic20 computer, but the cart itself seems odd. See what you think, and
post your comments here, or email me directly. Whichever. (BTW, I'm not
trying to sell it; just confirm my suspicions on it.)



General description of the Vic20 "Tooth Invaders" cart I found:

The cartridge body is made of dark brown plastic, like most of the Vic20
RAM or utility carts were, instead of tan, like most (all?) of Commodore's
own Vic20 game releases were. That in itself is a little abnormal, but
only to a Vic20 cart collector; no one else would know or notice.

Commodore's Vic20 carts usually had one of two types of labels. This
cartridge label is the thin, lightly-brushed sheetmetal type, not the
plastic kind. It has an embossed or raised edge around it, and the
silk-screened label text is brown. So far, fairly normal.

But where the name and part number of the cart would normally be
silk-screened (painted) on, this cart has its name on a seperate, good
looking, silver-colored stick-on decal, approximately 7/8ths inch tall and
2 inches wide. It was placed very carefully, and even looks like brushed
metal itself, so that it matches the label underneath it. The metal label
itself appears like it was made for that type of add-on-later labeling. In
other words, besides a few fairly standard looking, generic Vic20 arrow
and line graphics painted on, and the Commodore name and logo, the main
label underneath was blank from the factory. The add-on sticker does
closely match the labels color, so it really looks like they did this all
on purpose, with much pre-planning, and with an eye towards good overall
looks. Plus, the sticker itself appears to have a glossy clear coat on top
of it, somewhat like thin lamination, perhaps to protect the name and part
number.

All of this I noted, vaguely, but I didn't do any real double-take until
the somewhat poorly-glued  sheetmetal label fell off, while I was cleaning
off a thrift store price tag. This exposed the interior PC board, which
had a reprogrammable EPROM chip, socketed no less, where a "normal" cart
would have had an unsocketed ROM chip. At this point, I was saying "What
the (bleep)...."

A few notes: you have to keep in mind that once you remove a label from a
normal Vic20 game cart, you see nothing but glue on bare plastic. The guts
are still completely covered up. But this cart had four large rectangular
holes under the label, or put another way, emptiness except for a
plus-sign-like center support molded in. This is somewhat normal for
utility carts, perhaps, but very odd for a Vic20 game cart, I thought. I
kept looking at it, and noticing more and more. The more I looked, and
thought, the less convinced I was that this was a normal cartridge. I
doubt its a prototype, as I'd expect that to be a bit uglier perhaps, but
definitely experimental.

General PC board description as follows. The circuit board has been
designed for two 28-pin, commonly available EPROM chips, instead of the
more common 24-pin Commodore masked ROM chips found in all production
carts. The board has standard issue Commodore-style jumper pads for memory
bank selection. Chip #U1 can be moved into memory banks 1, 2 or 3 by
soldering onto the small jumper pads, and chip #U2 can be placed in memory
at banks 2, 3 or 5 via the same method. But note that you have to do this
by hand by design; otherwise, each chip seems "invisible". Normally there
would be some default setting built-in, but this board forces you to
choose, or it won't work at all. My particular carts PC board is set for a
single chip at bank 5, which is normal for 8k Vic20 ROM programs. No
second chip is present. (The board's part number is 1900026, if that means
anything to anyone. The board has a copyright date of 1982 on it. It also
says it is Revision  A, that is was made in Japan. It has some more
markings on the bottom: "W-1794V-0".)

Overall, the board itself looks like it was mass made, not one of a kind.
It is a quality job, mind you, but the small
bend-to-break-this-one-off-from-a-larger-board tabs are on the board's top
and left edges, telling me this board was designed to be made in some
quantity. But it does appear that the thin gold (anti-corrosion) plating
that is normally found only on card edge fingers, is on all the traces
everywhere. It appears to be that way under the green solder mask coating,
and is definitely that way on all exposed solder pads and jumpers. This is
a bit unusual in itself. I'd say that while it looks at a glance like an
off-the-shelf Commodore part, mostly, its definitely one of their best
quality parts! (Some production Vic20 games didn't even have gold edge
finger plating, let alone gold plating on every trace and pad on the
board!)

Commodore's usual masked ROMs were 24-pin devices, while the common "2764"
type of 8k EPROMs were 28-pin devices. So while this seems like maybe its
a standard "off the shelf" PC board, some thought about it says it can't
be a normal production part. A standard 2764 EPROM chip wouldn't even fit
in a board designed for Commodore's "normal" masked ROMs, let alone work,
as the EPROM has four extra legs. So what's going on here? Did Commodore
have some very high-quality circuit boards made up just for carts like
mine? It seems like they did.

Another thing to consider is that the combination of a standard IC chip
socket, plus an EPROM chip, would make the whole thing too tall to fit
into a normal game style case. This probably explains the
odd-for-a-Vic20-game case; nothing else would fit this combination of
parts. However, the RAM expander / "utility" style cases were apparently
designed and molded to clear taller combinations, and were off-the-shelf
parts to Commodore. (In all other major respects, both case types are
basically identical.)

This seems to me to be getting weirder now, all around, but with a pattern
developing, perhaps.
Correct me if I'm wrong, or confirm that this makes some sense; you
decide.

For "them" to have used an EPROM chip instead of a masked ROM chip would
have increased Commodore's costs. EPROM chips cost more per unit than
ROMs, even ignoring the PC boards made especially to fit them. And
remember, Commodore owned MOS, a chip-making company; that would have cut
their masked ROM costs even lower than normal.

So I tend to think that for carts like mine, they didn't seem to care
about unit cost ... which is very, very odd for ultra-frugal Commodore!
Anyone who knows Commodore, will likely agree!

And at the same time, they seemed almost obsessed with having all the
major component parts being the best available. Even the off-the-shelf
items were the best they had, seemingly.

Remember the gold plating over the entire PC board surface? Ditto for the
chip socket, which was soldered in by hand; mass production boards are
wave-soldered by machine instead. Plus the extra cost of the chip socket,
itself, which Commodore generally tried to avoid using.

All these parts are high quality, including the labels themselves. Why?
Commodore was a very frugal company. There must have been a good reason
for these expenses!

My best guess is that I (luckily) stumbled across a magazine review cart
or some such. A cartridge that was perhaps meant to be sent out for
reviews of their new products, as they made them. I'll entertain other
guesses, but it makes sense to me for a number of reasons.

This would explain their apparent obsession with quality and reliability:
who would want a new product to fail during its review period? Commodore
did have a reputation at the time of being more reliable than some other
contemporary companies, so that fits as well.

Plus it fits nicely that most of the parts were perhaps unusual, but still
off-the-shelf items. Commodore techs could hand-assemble a limited
production run very quickly, this way.

Once they had designed and ordered the generic EPROM-compatible PC boards,
they too became off-the-shelf parts, ready for use in any future products.
(Remember the built-in design flexibility, with the memory bank jumpers,
no preset default values, and selectable single or dual ROM chips, for an
8k or a 16k game? Does all that make sense now?)

Basically once they did some one-time planning, all they had to do was a
bit of soldering and hand assembly, "burn" an EPROM, slap a blank, generic
sheetmetal label on the cart, and make up a name sticker for it.

Well, what do you all think? Am I right, or is there another explanation
I'm not seeing?