How do you fix an Atari 2600.No video is coming out but it is on.

ok try these.
make sure the RF box is properly connected

make sure your TV is on the correct channel.

if that does not work try these:

take the cartridge you are trying to run, and locate a screw on the cartridge case. unscrew it and remove all the contents. place only the game chip into the console and turn it on to test the game. if there is still no picture, place the chip in backwards and retry.

or try this

disassemble on the console with a #2 Phillips screwdriver. there should be a silver box. dismantle it and turn it right side up to find a white knob. slowly adjust it and see if any picture appears.

if that does not work, then it is busted.