Instructions
Hold open the cartridge-slot cover with your thumb and turn the Super Nintendo upside down to let any loose dust fall out of the console.
Wrap part of a T-shirt or other cotton cloth around a credit card or similar item. You must wrap it very tightly so that it will fit into the connector and not catch the sides as you pull it out.
Pour a small amount of rubbing alcohol onto the cloth, or pour the alcohol into a container and dip the cloth into the alcohol.
Insert the cloth into the cartridge slot so that it can clean the connector pins, and then pull it out. You will likely see some dirt and grime on the cloth.
Shift the now-dirty cloth on the credit card to a clean section; then insert the cloth into the console again. It will take two or three insertions to clean the length of the connector pins; use a clean section of cloth each time.