So the parts arrived! I ended up changing out five capacitors, the ones used for the main power as well as one used in the five volt circuit. I also swapped out the voltage regulator. On eBay there were a number of “refurb kits” so I decided to order one of them. I also swapped out the two capacitors used in the audio circuit, though when I had completed the upgrade I discovered this was not totally necessary in this particular instance. The audio circuit uses two polystyrene capacitors that were notorious for failing or affecting the sound quality.
The next phase was to convert the video output from the legacy RF modulator and make it a composite output. This way the console can be plugged directly into the RCA jacks on modern TV’s rather than through the cable jack on the back, which would require you to put the TV on Channel three to see the picture. The composite is supposed to be a better quality picture to boot.
You can order a composite upgrade board from some vendors on the internet, but I stumbled across a schematic for one that someone had built using a transistor, two resistors and a perf board. Since I had all these components on hand I decided I would just build my own.
The original circuit called for a 2N3904 transistor, a 2.2K and 3.3k resistor. I had a 2N4401 transistor, 2.2K resistors and some 1K resistors. The specs on the transistor were pretty close and I tied one of the 2.2k and one of the 1K together to get 3.2k (pretty close). I soldered them all together on the perf board, added wire for 5V, video and ground and I was ready to hook it to the Atari. I removed the RF modulator and a couple of resistors which effectively disables the original audio and video circuits. I was ready to hook up my new composite video board!
The Atari has it’s own custom chip that outputs the video and audio. You are basically taking the signals directly from that chip. The audio is mono, so the two audio jacks are tied together, the video signal goes through the board and boosted through the transistor.
I hooked everything up and tried it out.
Amazingly it worked!
So what’s next? Something a bit more ambitious. I want to use a modern XBox controller to replace the vintage (very non-ergonomic) Atari Joystick. I will probably use a Raspberry Pi and some Python coding to get that going.
Pictures and video below.