Do NOT... EVER... Turn pots on pickups, or cd players anyway. The fastest way to kill a laser is to fool with it without knowing how, or without owning a laser power meter.
Also, static electricity will kill it.
Do not attempt this without an anti static mat and a ground strap around your wrist. You will also have to unsolder (most pickups) a safety jumper to protect the laser diode.
If you are lucky, it'll work as is. But often the focus and tracking has to be re-adjusted. For that you will need a scope and some experience knowing what you are looking at. These adjustments are in the player. The pot on the pickup is adjusted at the factory and must never be touched. Some people will turn this up a little to push a little more power out of the laser in order to sell the player.
This trick only lasts a short time, but usually long enough to wash their hands after the sale.
On your player, the only sure way to know if the pickup is ACTUALLY bad is to measure it's power.