Why did you have to blow into an NES cartridge to make it work?
Did doing this actually help at all? If so, how?
Solution 1:
Popular belief among those of us who remember the original NES held that that blowing into an NES cartridge removed dust from the contacts, which allowed a better connection to the system. In practice, the method was similar to the following:
- Plug in cartridge, turn on system
- Curse when system does not work
- Pull out cartridge, blow
- Re-seat cartridge, try system again
In a few cases, blowing may have actually removed dust, but the truth is that most of the time, what actually fixed the problem was the act of pulling the cartridge out and putting it back in.
As the original NES required you to put the cartridge in and then down, another common trick was to shove a second cartridge in the slot on top of the first one, which prevented the bottom (game) cartridge from slipping.
Finally, Mental Floss has a detail analysis of the effects of blowing in an NES cartridge.
Solution 2:
For the most part, it didn't do anything. When the system didn't work, most people's natural assumption was that the connectors were dirty. The most logical way to clean something like cartridge connectors was to blow on it. They also sold cleaning kits, but in my experience they weren't actually that helpful.
The problem wasn't the cartridges, but the connectors in the NES itself. According to Wikipedia, the problem is due to Nintendo's use of a "zero-insertion force" cartridge connector:
When a user inserted the cartridge into the NES, the force of pressing the cartridge down and into place bent the contact pins slightly, as well as pressing the cartridge’s ROM board back into the cartridge itself. Repeated insertion and removal of cartridges caused the pins to wear out relatively quickly and the ZIF design proved far more prone to interference by dirt and dust than an industry-standard card edge connector. Exacerbating the problem was Nintendo’s choice of materials; the slot connector that the cartridge was actually inserted into was highly prone to corrosion.
Further, Nintendo used the "10NES" lockout chip, which required constant communication with the cartridge to authenticate it as a legal cartridge. When it didn't have the communication, the result was "the blinking red power light, in which the system appears to turn itself on and off repeatedly because the 10NES would reset the console once per second. ... Alternatively, the console would turn on but only show a solid white, gray, or green screen."
Solution 3:
Another popular theory is that the moisture from your breath was able to increase the conductivity of the contacts and increased the chances that they would successfully communicate.