DIY live has some good tips on fixing that old NES “I took apart my nintendo, and found the 72 pin connector. I took my smallest flat head screw-driver and pried every pin up a little. Over time, they had lost their springiness (I don’t know if that is a word, but it describes what I am talking about). This is a pretty good fix. It may not be the best, but it works. Another thing to help out is to clean the pins of your old cartridge. You can take a wooden pencil with the red eraser, and rub it on the pins of the cartridge. Make sure you get all of the eraser off of the cartridge.” Thanks Star! Link.
HOW TO – Fix your old NES