The discharger current is fluctuating.
The discharger current control voltage is at maximum or minimum, indicating that the current is too high or low respectively.
Remove the top cover of the instrument.
Disconnect the discharger coaxial plug.
Unscrew the discharger needle holder. You may use narrow pliers or tweezers in the two holes.
Check that the o-ring around the base is in good condition.
Grab the needle from the neck holder with tweezers or pliers and carefully pull it out.
Carefully scrub the needle with tweezers or a sharp knife.
Push the needle back in. Make sure the needle remains straight.
Screw the discharger needle holder back.
Reconnect the discharger coaxial plug.