Hobbs Meter Stopped Working

[231MJ]

Hobbs meter not working.  Airplane = M20K 25-0308.  Would appreciate advice on trouble shooting.  Specific questions:

1. What drives the meter - oil pressure switch?

2. If I put 12V to the meter, should it run?

3. Is there a fuse or CB in the circuit?

4. What am I not asking that I should be asking?

Thanks

[N231BN]

Here is the schematic for your airplane, I don't have time to look through it right now but I don't think it is on there as it was still a factory option at that time. My '79 uses the "AUX" terminal on the alternator to power the hobbs. If yours is the same there should be a fuse holder in a wire coming from the alternator in the engine compartment.

M20K-F3.pdf

[daytonabch04]

Mine stopped in my Bravo within the past 50 hours as well.

[PT20J]

Installations with electric tachs drive the meter from the tachometer and begin recording once some minimum rpm is reached.  Installations with mechanical recording tachs drive the meter from the alternator aux terminal and record when the alternator voltage rises as the engine reaches some minimum rpm.

Skip

[N231BN]

Installations with electric tachs drive the meter from the tachometer and begin recording once some minimum rpm is reached.  Installations with mechanical recording tachs drive the meter from the alternator aux terminal and record when the alternator voltage rises as the engine reaches some minimum rpm.
Skip

All 231's had electric tachs. The first couple of years they still used the alternator to drive the hobbs before they switched to the newer style tach.

[231MJ]

Thanks, 231BN, there are several fuse holders on the copilot side, I'll start there.  The schematic is also great but takes young eyes and patience to trace, but I'll try.  Back to the hangar this weekend.    I'll keep you-all posted as to what I find.

August

[PT20J]

If your Hobbs Is driven by the alternator, the fuse should be located at the alternator. Check there first.