Since we have an Atari 2600 discussion on the board.... 
I have an Atari 7800 that I would like to get working. The unit powers up, but regardless of what cartridge is inserted I get nothing but colored vertical bands on the TV. On a rare occasion the game will start. The last time I tried to get it working I used a cartridge cleaning kit on the cartridge and the slot connector.
Oh how nice it would be to be able to play Food Fight, Robotron: 2084 and Xevious again without an emulator!
Open it up and check for broken solder joints, most especially in the power supply and where the cartridge plugs in.