Atari 7800 plays 2600 games but almost never 7800 games

[Aussie2B]

Okay, so I've cleaned every single one of the 2600 and 7800 games I found, all with the same cleaning method, and all ten of the 2600 games work perfectly, always loading up on the very first try. Meanwhile, none of the seven 7800 games are working. I don't know why I was able to get Centipede to work that one single time before, but I haven't been able to replicate that, not with Centipede or any of the others. The best I can get with the 7800 games is a scrambled Atari logo screen. If I let the system sit on for awhile, it gets less scrambled, but never enough to actually work properly.

I tried reseating all of the socketed chips, but that didn't make any difference. I did notice a spot of corrosion around a pin of the MARIA chip, which I cleaned up, but I don't know if that's a sign that the MARIA chip is failing.

The power switch seems to be working fine. The light always comes on in conjunction with it, and I've also done a lot of testing with the board outside of the system shell, pushing the switch directly rather than via the plastic button.

We also tried messing with the pots. The color pot works as expected, but the pot closer to the cartridge slot seems like it's doing absolutely nothing.

[AdamAnt316]

Okay, so I've cleaned every single one of the 2600 and 7800 games I found, all with the same cleaning method, and all ten of the 2600 games work perfectly, always loading up on the very first try. Meanwhile, none of the seven 7800 games are working. I don't know why I was able to get Centipede to work that one single time before, but I haven't been able to replicate that, not with Centipede or any of the others. The best I can get with the 7800 games is a scrambled Atari logo screen. If I let the system sit on for awhile, it gets less scrambled, but never enough to actually work properly.

I tried reseating all of the socketed chips, but that didn't make any difference. I did notice a spot of corrosion around a pin of the MARIA chip, which I cleaned up, but I don't know if that's a sign that the MARIA chip is failing.

The power switch seems to be working fine. The light always comes on in conjunction with it, and I've also done a lot of testing with the board outside of the system shell, pushing the switch directly rather than via the plastic button.

We also tried messing with the pots. The color pot works as expected, but the pot closer to the cartridge slot seems like it's doing absolutely nothing.

What about the contacts within the cartridge slot itself? I believe the outer sets of pins are involved with telling the system to engage 7800 mode, though I could be wrong. I don't think corrosion is a direct sign of a failing chip, though cleaning it off and ensuring that each pin is making a good connection with each contact in the socket would be a good idea (if the pin contacts within the socket show signs of corrosion, it might be a good idea to replace the socket). Some info on troubleshooting a 7800, as well as a theory of operations, can be found here. Technical specs, as well as info on how MARIA does her thing, can be found here. Good luck!
-Adam