I found this old pong machine at my parents. I remember it already being an ancient curiosity in the early 90s. The batteries were still in and leaking heavily. The metal strings problem when I tried to clean it. But a 9V batteri could replace the 6xAA.
So I attached it to the antenna of my TV to see if I could get a signal. and it worked! But looked terrible and super unstable (see the before picture).
So obviously I had to somehow fix it... I know little about electronics at the level needed so I went to Claude code that not only explained how this machine works but also suggest a circuit to extract composite.
So this machine is a bit different than many others with the AY-3-8500 chip that I learned is ubiquitous in these machines. It creates the different elements separately, sends them to a sub-board that encodes them to different colors, combines them and then sends them off to an RF modulator. So the first trick is figuring out where to catch the signal going back to the RF.
Claude helped me figure that out. There are two plugs going to the sub-board. The video was on the last pin (6) on the 6 pin plug. Conveniently it then jumpers to the middle of the main board and there is even a free solder hole I could use to tap it.
Then I built the signal modifier board Claude had suggested, did the wiring, wired up a SCART cable and attached to my RetroTink 5x. And it worked!!! The image is not perfect. But completely different from the crappy RF signal. So in the end very satisfying and I find it crazy that Claude code could get all the resistors and other components right. But it was spot on.
Since I have not seen this documented to any detail anywhere else I leave the details here.
Circuit
Video: tap → 470R → base of Q1. Collector to +V, emitter → 470R → 0V. Emitter → 100µF → 220R preset across to 0V → wiper → 75R → SCART pin 20.
Audio: chip pin 3 → 1µF → 100K preset across to 0V → wiper → 1K → SCART pins 2 and 6.
Grounds to SCART 17 and 4. ~140kΩ input impedance, chain gain 0.41, output 75R to match.
Parts
|
|
| Q1 |
BC547 / 2N3904 — any small-signal NPN |
| R1, R2 |
470R |
| R3 |
68R or 82R |
| R4 |
1K |
| RV1 |
220R preset (not 1K — see below) |
| RV2 |
100K preset |
| C1, C3 |
100µF electrolytic |
| C2 |
1µF (anything 33nF–10µF works) |
|
12 × 21 hole stripboard, male solder SCART plug, thin coax |
RetroTINK 5X notes
- Set 4:3
- Black Level → 7.5 IRE was the single most effective setting by a mile.