The System Changer, developed under the code name Portofino (after the Redondo Beach hotel where the first design meeting was held), was introduced in 1983 just so Intellivision could be advertised as the system that played the most games.
Many people expressed amazement that the Intellivision's processor could emulate an Atari 2600. Well, it can't. The System Changer is itself simply an Atari 2600 clone -- essentially a 6507 processor, a TIA (Television Interface Adaptor) video/sound chip, and a 6532 RIOT chip (128 bytes RAM, I/O ports, and a general purpose timer). The System Changer only uses the Intellivision for its power supply and RF modulator.
(The Intellivision reads the System Changer as a game cartridge called M Network and actually draws an M Network title screen. With no cartridge in the System Changer -- hence no external video signal -- this title screen is displayed on the television. When a cartridge is plugged in, the external video signal takes over the RF modulator, displaying the output of the System Changer, instead.)
Although Atari threatened to sue, Mattel's lawyers concluded that it would be legal to clone 2600s since they contained all off-the-shelf hardware and no copyrightable software (as an Intellivision or Colecovision does). No lawsuit appeared, and clones started appearing from other companies.
Don't bother opening a System Changer to read what the chips are. Instead of being housed in the familiar DIP (multi-pin) packages, the integrated circuits are soldered directly to the printed circuit board using microscopic wires, then protected with a blob of epoxy. This cost saving technique was also used in most of the later game cartridges.
The only problem was that the Intellivision doesn't have an external video input. The Intellivision II was designed with the System Changer in mind -- it can accept an external video signal on pin 2 of the cartridge port and pass it to the RF modulator.
Intellivision (and its clones -- the Tandyvision One, Sears Super Video Arcade, any of the INTV Master Components) requires a circuit-board modification. Mattel used to perform this modification for people who brought their units to a service center.
Following are the instructions used by the service centers for making the modification.
- R23, 300 ohm 1/4W resistor
- R24, 3K ohm 1/4W resistor
2. CUT FOIL:
- COMPONENT SIDE:
- At the pad for R24 on the end that leads to Pin 1 of the RF modulator.
- FOIL SIDE:
- Cut the foil attached to J1, Pin
- Cut the foil at the pad for R3 (22K ohm 1/4W resistor) that leads to Pin 1 of the modulator.
3. INSTALL THE FOLLOWING:
- COMPONENT SIDE:
- A 1N914 diode with .250" length of sleeving on the anode lead. Anode lead to the foil leading to Pin 1 of the modulator using the feedthrough hole on this trace. The cathode to the pad for C33 (the pad at the end of the foil leading to R3).
- A 1N914 diode across the cut foil of 2.1 above, with the cathode to the pad for R24.
- A 2" length of insulated jumper wire from the cathode of diode CR8 to the junction of the foil between R3 and R9.
- FOIL SIDE:
- A 6" length of coax, #RG174/U, stripped 1/4" at each end. Shrink sleeve insulate exposed braid on one end and solder center conductor to J1 Pin 2 (i.e. braid is not connected). Other end solder braid to ground foil at C33 and center conductor to cathode of new diode installed at 3.1.2 above.