So, I got my 2600jr from eBay today. Bad sign - it had already been opened, since three of the plastic screw posts were broken, meaning that only two screws were keeping the case closed. In addition, all three of the metal shielding pieces were missing. Still, nothing seemed amiss as far as the board itself was concerned, so I went ahead with the most basic composite video mod (at the moment, I have no way to connect via RF).
Everything went fine with the wires and the soldering and everything, so I put the case back together, put in a copy of Space Invaders (my only cart at the moment), and turned it on. This was the result:
I find it hard to think that it is a failure of the video mod, because in that case I'd either have no picture at all, or just a very dark picture as is often reported with this very basic mod. Without the cartridge inserted, I either get a black screen or a black and white version of this pattern (the color/BW switch itself seems to have no effect either way).
Is this a hopeless case? What could cause this kind of failure? Should I just extract the cartridge slot as I originally intended for the Flashback 2 mod, or is there something I else I can do or test for in order to see if I can get this 2600jr working properly? It isn't likely to be a bad cartridge, is it?