I've got a front-loader NES that's giving me no end of trouble. I picked it up this weekend and, too my total lack of surprise, wouldn't play games. So I went about the normal process of disassembling it, cleaning the connectors, disabling the 10NES chip, etc.
No luck. Most of the time I get a blank white or purple screen. I will occasionally get Super Mario sounds (I've been testing with a SMB/Duck Hunt cartridge that I can verify works).
So I ramped it up and went after the connector on the main board with Brasso. It got a lot of nasty stuff off. I reattached the 72-pin connector and the load tray and it worked! Or at least I got the SMB/Duck Hunt intro screen. But it's only worked that once. Since then I get the same blank screen most of the time. I still occasionally get those sounds, and more rarely I get a very corrupted intro screen.
So I went to town on the 72-pin connector. Isopropyl alcohol, 600 sandpaper, the whole thing. Still nothing. So I ordered a new 72-pin connector. I got that yesterday. I plugged it in and got the exact same result.
Where do I go from here? Do I just keep on using Brasso until no black stuff at all comes off? Or could there be another culprit — maybe a bad IC? I can post pictures of the main board this evening if it will help.