Anyone who collects retrogames has undoubtedly popped a newly purchased old game into their favorite console only to be greeted by a blank screen or the dreaded blinking system light. Most people will reinsert the cartridge once or twice, and when that fails, they'll resort to the trick they learned when they were kids: just blow into it.
WHAT ARE YOU DOING, YOU MONSTER?! STOP DOING THAT!
"But it worked when I was a kid," you'll say. Yes, but you were stupid when you were a kid. We all were. Now you're an adult, hopefully wiser, and not a goddamn savage.
I'm not saying blowing into an old NES cart was a placebo. It was often the trick to getting games to work. The problem is why that trick worked.
You see, blowing into a cartridge basically coats the connectors with a thin layer of moisture as your breath reaches room temperature. Since water, and indeed moisture, are conductive, it's conceivable that it helped transfer electricity from the cartridge slot in your console to the gold pins inside the cartridge. Over time, however, that moisture will eventually corrode those same pins, making your beloved games look something like this:
When it comes to old games, years or dirt, dust, and moisture can render a cartridge unplayable, but that doesn't mean you have to throw out the cart and buy another. There's an extremely simple and inexpensive fix that only takes a minute or two.
The first thing you'll need is a way to open the cartridge. To prevent bootlegging, Nintendo and Sega both used special security screws in their cartridges. Gamebit screwdrivers are your answer, and they're readily available on eBay, various game stores online, and your local game shop may even sell them too (mine does) for around $10 (or less). Unfortunately, Nintendo and Sega did not use the same security screws, so you will need one of each gamebit if you want to properly clean all your carts.
It's also worth noting that unlicensed NES games used yet another different screw, this time with a star-shaped indentation. Most modern PC repair kits should have a bit that will work to open these up, and you may even have one in your standard toolkit for your home. The catch is that, at least for Tengen games, you'll have to pierce the label on the back of the cartridge to access a screw. If you're really anal about the condition your carts are in, this may pose a problem. Personally, I couldn't care less about the label on the back of a cart telling me not to open it. Screw you, label! It's my cart now and I'll open it if I want to!
Anyhoo, once you separate the plastic casing, you'll probably be surprised to see the PCB (printed circuit board) is smaller than you expected. For NES games, it's probably one-quarter the size of the cartridge housing itself, which makes me wonder why Nintendo of America wasted so much plastic when the original Japanese Famicom carts were closer to the size of a cassette tape. Regardless, remove the PCB and get yourself one of these:
Yes, that is an eraser. Sorry, you can't enlarge the picture, but why would you want to? It's a friggin' eraser. You can find them in art shops, your local CVS or Rite Aid, Target, Wal-Mart, probably that one aisle in your grocery store, and numerous other places.
Take your eraser and scrub it over the gold contacts on the board. There's no need to be too gentle. It may look like a delicate piece of electronics, but PCBs are very resilient. Just try to hold it around the edges to avoid bending any diodes. With some good scrubbing, you should see the dirt and years of accumulated grime wipe away, and the eraser shavings are easily cleaned up.
Next, you'll need a bottle of isopropyl alcohol. Most drug and department stores sell this, and you want the highest concentration possible. Anything over 90% should do fine, but if you want the best stuff, you can find 99% on Amazon. The higher the concentration, the less water is in the mixture and the quicker it will evaporate, leaving no residue unlike your filthy breath and spittle from your mouth.
Dip a Q-tip into the bottle and scrub both sides of the contacts with it to clear off any excess shavings and any remaining dirt. Use the other side to help wipe away excess alcohol, though it will likely dry almost instantaneously after application.
By the time you're done, which probably took all of one minute or two at the most, your cart should now look like this:
Put the PCB back in the housing, screw it shut, and pop it into your system. I've yet to purchase a single cart that hasn't been made like new again through these simple techniques. I've seen some other people recommend Brasso, which is a polish, but it's also quite abrasive and can strip the pins of their gold coating so I wouldn't recommend it personally.
You can also apply these techniques to most carts inside their housing if you don't have a gamebit, but why wouldn't you just buy one? They're like $10 each. Don't be a cheapskate. If you're spending money on old video games and consoles, you can afford to make a small investment to keep them working. The other benefit is you can verify the game you just bought is genuine by opening it up. Pirated games are easy to spot with a cursory glance at the board and almost no prior knowledge. They're really obvious, and you'll want to make sure that copy of Little Samson you found on Craigslist for $200 is real (ProTip: if you only paid $200, it probably isn't).
The moral of the story is DO NOT blow into your cartridges. Treat them with the tender love and care they deserve so future generations can hopefully enjoy them too.