Hi, I've found through the internet a great way to fix and clean the Nintendo system & to clean the game cartridges so they can play. I got interested in using my NES after viewing how much RBI Baseball is closer to simulating the sport than other games (even for the more powerful systems, since there are some badly simulated ones out there). So, I read in a few websites that show how to fix the contacts in the system and how Brillo and Q-Tips work for cleaning, although I've used MAAS gel and Q-Tips. Below are some images that show how I did this (*note : the only thing missing are images showing how I fixed the system's contacts - I will add them later, for now I'll explain how I did that).
First, I'll explain how I fixed the contacts in the system - on the internet, there are many websites that explain how to fix the contacts, and almost all of them use the same method. You would have to open the casing of the system, remembering the placing of each screw once they are taken out; next, remove the metal shell that covers the system board and contacts (again, try to remember where each screw went). Then, remove the motherboard (and remember where the screws where placed).Then, remove the black casing that holds the contacts from the motherboard ((and be sure to remember the placing of the screws). After, remove the part covering the contacts; now, using a small pin-like object, like a PIN or MINI SCREWDRIVER, go under EACH CONTACT and BEND them upwards until they almost touch the top part of the area (each one). After you're done (and it would take some time if you do this), place everything back (and check how the black casing is placed on the motherboard, there is a small hook on one of the edges), and place all screws back (it would help to have separate mats to feep the screws organized).
Now, as in the picture, I apply a little of the gel on a Q-tip, then gently apply visible coating. Next, using the cart with the coating left on it, I inserted the cart in the machine - some websites say to put a cart in the machine three or four times, for me it was OK with three. After, the third try, I used a clean Q-Tip to rub on the contacts of the game cartridge. If you try this, you might for the first try get the Q-Tip really dirty, since we're cleaning brass and there can be dirt collected in the machine's contacts after much time and playing, mine's definitely got alot of dirt (see photos). Also, you can repeat this step about three or four times, if you'd like.
Finally, if you've already cleaned the system contacts like in the above step, or they're fine how they are, you can clean the game cartridge contacts alone by rubbing them with a smaller application of the gel, then use a clean Q-Tip to clean what's left on the contact. Check to see that it works - also, there are many sites that give guides to do this - either way I hope it works for you as it did mine, :)
I restored a friends NES he bought off craigslist by taking it apart and boiling the black piece and bending the pins back down. Took 1 hour. Good stuff thanks for sharing.
Weinman cooktop cleaner for nes games does wonders.