It sounds like it is an open circuit or an intermitant connection. Check the wiring circuit for continuity.
What I found?
Mine was the low rpm controller located under the left side of the instrument panel.when open it is attached to the panel that is swung open it’s a small grey box.
first the hr meter stopped working on a flight. I decided to fly a known time and the low rpm warning came on during the low rpm test when the collective was raised while at 100%. We took a used controller and hooked it up and the problems were resolved.
Hi...i am new to these meters and don't have much knowledge but i observed that some hour meters are wired so that they start running as soon as power is applied, but this means that they turn even if the motor isn't running. On my engine have a positive feed from the ignition, a negative to the battery and a run terminal that comes from the alternator warning light.