OSS Supercart Hacker's Guide|
Welcome to Supercart Hacking! I'd like to start out with the standard "mod disclaimer"... to please proceed at your own risk, and that I cannot be held responsible for any damage to your Supercart, Atari, house, neighborhood, or for that matter, any injury to yourself or others. Please be careful and get some help if you are not experienced with soldering.
Phase 1: Busting the Cart Open
So, the first problem with hacking the OSS Supercart is getting the darn thing open. If you have an orange cart, no problem, just gently pry the case open with a small flat-head screwdriver. On the other hand, if you have a black cart, you've got some trouble. The cart shells are tightly glued together with some kind of heavy duty epoxy. I have opened over a half dozen of these carts so far, and have learned a few things in the process. Here's my current favorite method:
1) Small table vice
2) Soft cloth
3) A "box knife" (i.e. a utlity knife that uses rectangular shaped razor blades)
4) A hammer
5) A good dose of patience
1) Get everything together in the configuration pictured below:
2) Lightly tap the knife with the hammer along the crack between the front and back shells, starting from the bottom "fins" and *slowly* cutting toward the top of the cart. Be careful that the razor does not stray from the crack. Take your time and be careful. You'll probably ruin your knife, but they are cheap and easily replaced. I've opened several carts with the same beat-up knife, but its best to have a very sharp blade.
3) Now you have a choice. If you want to just pull the board out and say, reseat or backup the eprom, you can stop cutting at the top corners of the cart and not cut into the label. This way you can gently pry the shell apart from the bottom and slide the board out. When you glue the thing back together (I usually use some really lame glue for this like Elmer's), it will be very difficult to tell that the cart was ever opened.
4) On the other hand, if you are doing major surgery on the cart, such as the 4-in-1 OSS Supercart Mod below, you'll want to just razor right on across the top of the cart and through the label.
Phase 2: What's In There?
If you've got an orange cart, you will see a compact board with a few small ICs, a resistor, a capacitor or two, and two 2764 eproms (8kb each). In general, the black carts are the same except they contain a single 27128 eprom (16kb), unless its a Writer's Tool in which case it contains a single 2764.
[Note as of 4-13-2002: why is the 8kb Writer's Tool a bank-switching Supercart? My guess is for copy protection, since it won't work without the bank switching... plus OSS probably had quite a few of these boards laying around!]
Check it out, here's my Writer's Tool board:
Phase 3: Repair
In all cases that I've come across so far, either the eprom is bad or needs to be reseated. Its much more likely that it just needs to be reseated. Just carefully pry it out with a small screwdriver or ic puller, and lightly polish the contacts with very fine emery paper. Be careful of static charge. Its best to ground your fingers (like on some aluminum foil on your desk) before touching any components.
Phase 4: The 4-in-1 OSS Supercart Mod
1) 1 working OSS Supercart board that banks on $D500,$D501,and $D509 (all black carts that I've seen so far have this banking hardware)
2) 1 27C512 eprom (64kb)
3) Eprom burner (or at least a friend who will burn you an eprom!)
4) 2 47k Ohm resistors
5) 2 micro toggle switches, or dip-switches, or a "numeric-rotater" toggle switch (which are easily removed from the rear of old broken down external SCSI devices... my personal favorite since they look very cool on an OSS Supercart -- see pics below!).
6) 12 inches or so of fine hookup wire (I like 30 AWG wire-wrap grade)
1) Before undertaking this task, you should verify that your cart board does in fact bank on $D500,$D501,and $D509 (from here on I'll refer to this banking scheme as "019"). The utility CARTDUMP, will dump the banks of OSS carts to disk. Furthermore it cleverly investigates the banks and names the files CARIMAGE.CB?, where ? indicates the lower 4 bits of the address used to enable the bank. If your board is 019 compatible, CARTDUMP will produce files named with extensions .CB0, .CB1, and .CB9.
2) Next, you need all four 16kb eprom dumps from 019 compatible Mac/65, Action, Basic XL, and Basic XE OSS Supercarts. These should be read using an eprom burner and concatenated together into a single 64kb file.
[Note as of 4-13-2002: Well... this is kind of a pain these days to find all four of these very rare cartridges in working order and in 019 format. I'm tempted to just post my 64kb file for download, since I've never been able to figure out who owns the copyright. Perhaps this would be a good way to bring the current owner of this code out into the open at last!]
[Note as of 5-01-2002: I just found out that some of the OSS copyrights are held by a certain well-known Atarian who has contributed a vast amount to all of us (hint: the publisher of Atari Classics magazine!) and that I am very pleased to respect his rights in regards to these fine software products, and would hope others continue to do so as well.]
3) If you are using 2 micro toggle switches, just drill holes in the cart shell to mount them. If you are mounting dip switches or a "numeric-rotater", a small file works well to cut an exact rectangular hole in the plastic to fit.
4) Here's the schematic of the circuit to build:
,----, O +-------------------------------------+ SW1|/ | +---+ | | 47K | `----` +------/\/\/------+ GND \/ | _ ____ _____ | 47K +-[_|1 U 28|--+--/\/\/--+ (bend up|A15 Vcc| | pin)| |_ | ,----, O | 27|_]----------+---------+ SW2|/ | A14|(bend up +---+ | | | pin) | `----` | 27C512 | GND \/ | | |..........|Thanks to Walter Lojek <firstname.lastname@example.org> for help with this circuit!
5) With the eprom out of the socket, bend up pins 1 and 27. Solder everything as shown above, directly to the eprom. This is a little tricky, but I've had good luck first melting an amount of solder on a pin, then reheating it just a bit and inserting the wire to attach. Be very careful to not use much heat, since the eprom could be damaged. For soldering two wires to one pin, with a little practice, you can actually melt half the solder blob and insert a wire without disturbing the other side. For grounding the switches, it works fine to use the negative side of the big capacitor.
6) I'm working on a custom label to stick on the completed project... stay tuned for a downloadable image ready to print!
Here's some shots of my completed project (click to enlarge the circuit details):
7) That's it! You can now select the cart of your choice with the flip of a switch. You actually don't even need to power down. Just change the switch and hit RESET. Cool eh?
written and html-ized by Dan Vernon -- April 2002