Since writing the the original NES restoration guide, I've now done about 5 of them, and I've learned something in the process - the success of the previous guide depends entirely upon how well-kept your NES was. Every one that I'd worked on thus far has been fairly clean, probably kept in a closet or under someone's bed until I got them. In these cases, bending the pins and applying a bit of alcohol does wonders for your system.
But this won't always be the case.
Recently, I discovered an NES with a cartridge connector that had something jammed in it. Cardboard? Orange peel? I don't know, but it's in there pretty solidly, and soaking didn't help break it up. Also, my 1.4mm screwdriver snapped trying to get it out.
So, one quick retraction - if your cartridge connector has food jammed in it, just buy the new connector and get on with your life.
...seriously, though, how in the hell did they manage that? The connector is inside a case, below shielding, and inside a cartridge tray. You'd really have to want to jam something in there.
Anyway, let's move on.
More on the most important bit - cleaning the connectors. Alcohol is great for cleaning electronics, but 20+ years of dirt, grime and corrosion may not be cleared with just a toothbrush and some alcohol. I'd had a particularly stubborn connector, no matter how many times I scrubbed it, Mario just wouldn't come out to play.
But today, it's running like brand new.
Fine-grit sandpaper was the missing key. Take a piece of sandpaper, fold it over, and insert it into the cartridge connector between the pins. If the sandpaper is too thin, wrap it around a credit card or something similar. If you have an emery board, that'll work even better, as the thickness is just about perfect and has sandpaper built right in. Do this gently, because it may pull back the pins when you pull it out, which could damage them.
After doing this for a while, blast the connector with compressed air to remove any sand that may have come loose, then do the alcohol scrub mentioned in the last article, to clear out anything that may still be there.
The sandpaper or emery board does what it does best - the abrasive surface removes all unwanted crap from the metal pins, leaving the pins bare and ready for clean contact. Having transformed this connector, I now recommend this for all NES restorations as a "just in case" measure. As always, be careful not to break the pins. Have fun!