I received a copy of Sky Shark for the NES as a partial trade-in at the shop. It wouldn't work, no matter how clean I got the cartridge. I popped open the security screws with a special bit and looked at the board. Everything SEEMED fine, but then I used a continuity meter to check the connections from the pins to the PRG and CHR ROM set. A single pin leading from the cartridge slot had a hairline crack. I took a bread tie, removed the outer wrapper, and used it to jump the gap in the trace. Works great now! Unfortunately, it's Sky Shark for the NES, so it's not a really GREAT game by any stretch. Still, a working cartridge is a good cartridge, right?