Input: 120VAC 60Hz 15W
Output: 9VDC 1Amp
Polarity: Looking into the power supply, negative is on the left, positive on the right:

                             _ 
                         ___| |___
                      - | 0     0 | +
                        |_________|
 

If you cannot find a 7800 power supply but are comfortable with a soldering iron, one possibility is to find similar connectors and solder them onto a more easily-found power supply. Try using an end connector from an old cordless phone battery. Caution: the connector will plug in to the 7800 either direction so one needs to mark polarity correctly.

Another possibility is to buy a more standard jack and just solder it in parallel with the original connector, then buy a power supply at Radio Shack for a few bucks.

One good place to solder alternate power connections is to the two joints on the underside of the board, located near the original power plug (the polarity is easy to follow because the traces from the power and to the barrel capacitor are polarity-marked). Either an external jack (1/8" mono) can be run through the old jack's hole (or a vent hole) -or- an internal jack can be installed where convenient such as the thick "strut" near the original hole or on the right side (when facing the unit for play). You can use a 2600 power supply; the only difference is half an amp, which the techies say doesn't matter much.

 CPU:            6502C (custom, NOT 65C02)
 RAM:            4K, high speed (mostly VRAM)
 ROM:            52K max
 Cpu Clock:      1.79 MHz
 Graphics Clock: 7.16 MHz
 Slot Config:    Most CPU lines + video/audio
 CPU Avail:      over 90%
 

Expansion Port Audio
There is no audio signal output on the expansion connector pin 17. Introducing an analog audio signal on this pin produces no results, whether this is because there needs to be a flag set in one of the I/O chips to enable external audio mixing (which I suspect is the case) or whether it is expecting a digital signal, I don't know.

• Jay Tilton's 7800 Chroma/Luma/Audio mod
  
• Mark Graybill's 7800 Chroma/Luma/Audio (S-video) mod.

• Sentinel
• Alien Brigade (joystick ok)
• Barnyard Blaster
• Crossbow (joystick ok)
• Meltdown

 Test decks:
             Serial #                           Board part#
 Deck#        72R4BR-  Country  Expansion port     CO25233-  Board Date
 -----  -------------  -------  --------------  -----------  ----------
   1    AT  8 5037836   Taiwan    Full port       001 REV A       84-25
   2    A1 76 5904610   Taiwan    Full port       002 REV A       87-17
   3    A1 77 5951337   Taiwan    Hole/no pins    002 REV A       87-17
   4    A3 87 5139813   Taiwan    No port         002 REV B       88-28
   5    A3 07 5298641   China     No port         002 REV B       88-30
 

Board part number/revision is taken from the underside of the board, just above the cart slot. The full number always begins with "CO25233." The boards' top side has a different part number, "CO25234," but no revision level is given. Board dates are also taken from the underside of the board, near the Atari logo. The notation is changed a bit to make sorting by date easier. They're really written like "2584" instead of "84-25," which would indicate the twenty-fifth week of 1984.

The carts tested were:

• Decathlon (2 different carts)
• Robot Tank (3)
• Space Shuttle (5)
• Supercharger (2)
• 7800 Food Fight

 Results:  "Yes"  = cart works fine.
           "No"   = cart doesn't do a thing.
           "Roll" = cart works, but picture rolls.
           "Lock" = cart plays for a while, then locks up the system.
 
                 Deck #
      Cart          1        2        3        4        5
                 ------   ------   ------   ------   ------
     Decathlon 1    Yes       No       No      Yes      Yes
               2    Yes       No       No      Yes      Yes
    Robot Tank 1    Yes     Roll     Roll     Roll     Roll
               2    Yes      Yes     Roll     Roll      Yes
               3    Yes      Yes     Roll     Roll      Yes
 Space Shuttle 1    Yes      Yes      Yes      Yes      Yes
               2    Yes      Yes      Yes      Yes      Yes
               3    Yes     Roll     Roll     Roll      Yes
               4    Yes     Roll     Roll     Roll      Yes
               5    Yes      Yes      Yes      Yes      Yes
  Supercharger 1    Yes       No       No       No       No
               2    Yes       No       No       No       No
      Food Fight    Yes      Yes     Lock     Lock      Yes
 

The manufacturing standards of deck #1 are better than the others. All the major chips inside are all socketed instead of being soldered directly to the board. Some of the other decks also have had some minor factory patchwork performed. They occasionally have resistors bridging points where they were clearly not originally intended to be, i.e. soldered directly to a chip pin or placed on the underside of the board.

Wondering if that 7800 deck sitting in the thrift store could be one of the fully-compatible ones? There are some very minor externally visible differences between my deck #1 and the others. These may not be 100% reliable indicators, but they are conspicuously different.

The labels on the undersides of decks 2-5 have a box drawn around the serial number. Deck #1 has no box drawn. The serial number itself on deck #1 is different from the others. The "72R4BR" prefix is very much smaller than the rest of the number. "AT85037836" is one continuous string of black characters with no spaces, while on deck #2 (#3-5 are similar), "A1 76 5904610" does have the spaces, and the "76" is stamped in blue. The cart contacts of deck #1 have a definite copper color, while the contacts of the others have a silvery appearance.

Superchargers may be permanently damaged when used on the 7800. Try Robot Tank first and then proceed only if that cart works.

The Atari History Museum has several of the original 7800 (AKA 3600) technical documents on their 7800 page (scroll to the bottom).

Eckhard Stolberg's VCS Workshop Page also contains many tools and source code files. Of particular interest is devkit2.zip which contains instructions on how to modify a 7800 such that it may be used as a development system and cart reader for 2600 and 7800 games.

There is Harry Dodgson's Monitor Cart plus documentation. The 250+ pages included a stella guide, a 2600 programming manual which was a bit more readable, the Maria specs, and the 7800 docs plus numerous corrections to the Atari documentation. Video 61, is still producing these in small batches. The price is $99.95.

The reason you need to encrypt the programs is that, as designed, the 7800 required a valid 960-bit digital signature generated by Atari before a native 7800 game (as opposed to a 2600 game) would run on the 7800; no digital signature, no Maria chip. Also, crypto export restrictions (960 bits are a lot even for military-quality crypto) are probably the reason that European 7800 consoles and games have no digital signature.

• Asteroids
• Ballblazer
• Centipede
• Crossbow (lightgun OK)
• Dig Dug
• Donkey Kong
• Donkey Kong Junior
• Fight Night
• Food Fight
• Galaga
• Impossible Mission
• Joust
• Kung Fu Master
• Mario Bros.
• Ms. Pac-Man
• Pete Rose Baseball
• Robotron: 2084
• Summer Games
• Super Skateboardin'
• Title Match Pro Wrestling
• Touchdown Football
• Tower Toppler
• Winter Games