What to do if there's a circuit cold solder joint issue?

Thoroughly inspect the solder joints on the circuit board for cold solder joints and promptly re-solder them.

Inspect electronic components for burn-throughs and replace them promptly; or directly replace the faulty circuit boards.

What to do if dirt or water enter the touch switch

Remove the corresponding equipment housing and inspect the severity of water entry into the touch switch. If not severe, use a desiccant to absorb the moisture. For stains, wipe clean with alcohol, then wait for the alcohol to evaporate before reassembling. Do not cause secondary damage to the device. If water entry is severe, consider replacing the touch switch with a new one of the same specification and function.