Model 3 RGB & mono
Model 3 RGB and the mono audio caveat
The Model 3 (the smaller, cost-reduced revision made by Majesco in North America) is often dismissed by collectors, but it has a few important quirks worth understanding before you build a cable or buy one secondhand.
It still outputs RGB
Despite its reputation as a budget console, the Model 3 does output RGB on its video connector, just like its predecessors. With a correctly wired cable it can produce a sharp picture, so it is not the dead end some assume. The DIN pinout differs from earlier models, so a Model 1 or 2 cable will not work directly.
The mono audio problem
The defining limitation is audio. The Model 3 outputs mono sound only. There is no headphone jack and no stereo separation on the AV connector, so games that mix instruments or pan effects across channels lose that dimension entirely. This is a hardware-level limitation of the board, not something a cable can fix.
Do not attempt to "split" the mono signal into fake stereo at the cable; both channels will simply carry identical audio. True stereo on a Model 3 is not achievable without significant board-level work that is generally not worth the effort.
In short: choose a Model 3 if you want compact RGB and do not care about stereo. If audio fidelity matters to you, a Model 1 or 2 is the better starting point.