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Eleven screws later, we finally have the console opened up. Kinda dusty inside, isn't it. You can thank all those ventilation slots in the top of the console for that; they allow a fair amount of dust to accumulate inside over 20-plus years! But we're not done with the screwdriver just yet; that metal shield is attached to the circuit board with still more screws, along with a soldered shield-braid. Boy, Coleco really didn't want this thing being taken apart once it was put together, did they...
The Colecovision's main board. Surprisingly few chips, really, considering the technology of the time... the largest two chips are the Z-80 CPU, at the bottom, and the TMS9928 graphics chip up towards the top (the one with the heat sink on it.) The single 28-pin chip in the middle is the BIOS ROM, and just above that is the SN76489 sound chip. Most of the rest of the chips are RAM, with just a few 74LS-series logic chips to glue it all together. Simple, but effective. One of the advantages to the Colecovision's design is that all of those chips were quite common and widely used, making information about them a lot easier to come by than the relatively obscure General Instruments components used in the Intellivision.
Incidentally – before we begin adding our modifications, now would be an excellent time to flip the PCB over and look for any suspicious-looking solder joints, particularly around the power switch and cartridge slot. A cracked or oxidized solder joint can wreak all kinds of havoc, from causing the system not to boot up at all to unexplained control failures and game crashes.
This is the simplest part of the conversion. The SN76489 sound chip has plenty of signal-drive capability and doesn't need any impedance-matching circuitry, so its output can just go straight to the RCA jack which will be mounted on the back of the console. Unlike the Intellivision, it doesn't even need any capacitive coupling to filter out any DC components (though it probably couldn't hurt any if you feel like adding it anyway.) Take some shielded audio cable and solder the ground-shield to pin 8, and the signal lead to pin 7. Smaller wires will be easier to solder, so I'd recommend using some thin audio-signal wire. You can either pick up some microphone cable from your local Radio Shack – or just do what I did, and scrounge the wiring from a set of ultra-cheap headphones from your local "everything's-a-dollar" store.