Here's how I fix NES's
1) Take the nes apart, and take the 72 pin connector out.
2) Take a pot of water, and bring it to a boil.
3) Using a thumbtack, bend all the little pins up some on the connector, you may see one side lower than the other.
4) Plop the connector in the water, let it sit 5 mins.
5) Pull it out. Show your wife. If she laughs, divorce her.
6) Out it away, and pull the nes connector out of the water. Put a
clean but cheap nes cart in the slow, wiggle it, just a little bit, and remove it. Repeat 30ish times.
7) Boil 5 more mins

Have cart intersex once more, another 30 or so pumps
9) Dry off the connector and cart with a hair dryer.
10) Double check the pins look pulled up good and are even.
11) Optional, and risky: Disable the NES10 chip. This will make it impossible for the nes to ever blink. If you ever see the game load but it blinks, the NES10 is the cause. It also lets you play unlicensed games that did not disable the NES10 chip.