If the LCD of the ammeter does not light up,

1. Check if the laser power supply is energized (as indicated by the lit power indicator),
2. If the power supply does not light up, see "Laser power supply indicator not lighting up ".
3. If the power supply lights up normally.

Check whether the signal line between the laser power supply and the ammeter has a secure contact (If your power supply and ammeter are assembled as a single unit, ignore this step and replace the laser power supply directly.).

If the contact is ok, then the ammeter is faulty and you will need to replace it with a new, identical one.