I fix these at work all the time.... Most of the time it boils down to a connectivity issue.... Seeing as I fix a dozen of these a week at work, I take the shortcut method by replacing the 72 pin connectors and removing the circuit that bypasses the security lockout and can get the whole thing done in 5 minutes.... I would say if you feel like there is a loose fit then the 72 pin connector is the primary problem to look at.... Some people try to lightly bend the connectors back into place, but I'm lazy and new pins are cheap enough.... It would be hard to explain without a diagram, but a youtube video can show how to disable the lockout.... Its the 4th pin on the chip closest to the ports on the backside of the system along the bottom of the board.... I can post photos if you'd like next time I do one.... Alcohol is definitely great for cleaning, but there is also something called Brasso that is excellent as well.... I usually clean the contacts on a board that connects to the 72 pin adapter before putting a new one on with that stuff.... It works great for cleaning cartridge pins as well.... I would use a Q-tip and clean with alcohol first, then with Brasso for maximum effectiveness.... If you've got any other questions regarding, then feel free to ask....