The problem could be a faulty battery. Try using it with the external power supply connected. 4V DCIn this video, we explain how to repair an Optical Power Meter that powers ON but does NOT show any optical power reading. Select. If you are having trouble with a Kingfisher PON power meter, please check the following: If the instrument has alkaline batteries, just replace them and try again. Try using. REF/dB key: Short press the dB to switch unit, click once nW/dBm/dB to enter the upper clear data, press and hold until REF is displayed on the screen, and set the current optical power as reference value, enter the relative optical power test mode, the screen will display the setted reference.