Disclaimer: I cannot be responsible for damages, monetary or otherwise, incurred by the use of these procedures. Anyone who attempts them does so solely at their own risk.
When to attempt this fix
It's a good idea to clean all your games and systems regularly as preventive
maintenance, even if you're not experiencing problems. But if you are
having trouble, cleaning may clear up the following symptoms:
1.Blank screens
2.Scrambled game graphics
3.Games that crash in the middle of play
4.Flashing screens and power lights
What you'll need
1.Q-Tips
2.Windex or a solution of 50% isopropyl alcohol, 50% water
3.Phillips-head screwdriver
What to do
To clean a cartridge:
1.Remove the screws on the underside of the system.
2.Turn the system over and lift off the plastic top.
3.Remove the screws holding down the metal RF shield and remove
the shield.
4.Remove the screws holding down the black plastic cartridge holder.
Note how the small plastic tab on the front of the holder slides
underneath the motherboard. Slide the holder forward and remove
(it's all right if the motherboard bends slightly).
5.Lift the back of the motherboard up and pull off the set of contacts
in the black plastic housing. (They will resist a bit; rock them
back and forth to slide them off.)
6.Dip a toothbrush (preferably not yours; use a loved one's) in the
cleaning solution and scrub contacts off.
7.Rinse contacts off with water and allow to dry.
8.Lift up the back of the motherboard and slide the contacts back into
place.
9.Lift up front the front of the motherboard and slide the cartridge
holder onto the contacts. Be sure the tab on the front of the holder
clips underneath the motherboard.
10.Reattach the cartridge holder's screws. (The long ones go in the
second set of holes from the back.)
11.Plug in the system and test with clean cartridges. (It's perfectly safe
to do so with the top off.)
12.If the games still won't work, the system contacts may be bent out of shape. Greg Lambert has written an article on fixing them, available at http://www.classicgaming.com/features/articles/nesrepair/.
Replacements can also be taken from another defective system or
purchased from some electronics dealers. Try MCM Electronics
(
http://www.i-mcm.com/) for starters.
13.If the system is working properly, replace the cover (you can leave
the RF shield off if you like, I won't tell the FCC) and reattach the
screws on the bottom.