First of all I have disabled the 10nes, cleaned, refurbished the 72 pin and have a GG to play games through to cure some boot issues. All test were with/without the GG.
I have 4 carts that are dead that I got off the bay.
1) Contra - will not boot up at all. Game has been cleaned with 70%/q-tip, Brasso. I did one at a time not together. The PCB part doesnt appear to have any loose connections but the connectors are worn.
2) Castlevania - The PCB is mint as well as the connectors......Looks like it has never been played. Its been cleaned as well even though it didnt look like it needed it. Im clueless on this one.
The rest I dont care about. What causes a Game Cart to die? I think I would at least get some glitchy graphics but I just get a gray screen. What can I do with dead carts?