How to Repair a Credit Card

The dark stripe on the back side of the credit card is made up of a bunch of tiny magnetic particles bound in plastic. The particles are arranged in magnetic and non-magnetic “zones” to encode the data, like your account number, expiration date, etc., that the card reader needs to process the transaction. When you swipe the card, the card reader reads the information by detecting the changes between the zones.

The strip is delicate, and the data on it can be corrupted by exposing it to a strong magnet or scratching it. Some of the magnetic particles can get dragged out of position. If enough magnetic bits move into a non-magnetic space to create a weak signal, the data gets corrupted and the card reader gets an error.

Applying Scotch tape to the magnetic stripe, encasing the card in a plastic baggie, rubbing the card on clothing, or wrapping the plastic in a dollar bill or a register receipt may enable a cashier to complete the transaction. Also, licking the mag stripe, applying and removing Scotch tape, or rubbing it on your clothes can remove dirt and debris that may be preventing the reader from accepting the card.

When the cashier puts the card in a plastic bag, it creates a spacer so the card slides through the reader with a slight separation between the data stripe and the stripe-reading head. The separation weakens the signal and cleans it up. With just a little bit of magnetic material in them, the contaminated non-magnetic zones still have a much lower magnetic strength than the parts that are supposed to magnetized. Increasing the distance between the card reader and the corrupted zones is enough to get the reader to read those weak parts as non-magnetized again.