Yanmar 2gm20 rev counter not working

[dlwilkes]

Had a bit of a nightmare with recently purchased 26ftyacht electrics mainly old spaghetti wiring bad earths old batteries and trouble starting
wiring all ok now and new batteries but rev counter stopped working.
any suggestions??/ with playing with the batterries have I "flashed" rev counter and scrapped it perhaps? any tests I can do or are they repairable?
Thanks

 

[Eygthene]

My Yanmar 2GM20 has a rev counter. If yours has the larger (Type B) control panel, make sure there is a good 12v supply to the rev counter between (red/black wire) and (black wire) on the terminals on the rev counter. Between the orange wire and the blue/red wire flow the pulses from the tacho. sensor, which really requires an oscilloscope to test the output, though a digital voltmeter should read about 1 volt AC between them with the engine running. If the fault has only occured since the rewire, these two wires have probably not been disturbed anyway.

If you suspect a faulty tacho sensor, you can check the resistance between these two wires (after disconnecting them from the rev counter) which should be about 1500 ohms.

My Yanmar has the simple (type A) control panel (ie no rev counter included), with the rev counter and fuel guage as separate instruments alongside it, but I am referring to the Yanmar service manual to help you.

 

[misterg]

Just to add to John's reply:

The tacho sensor is on the bell-housing (between engine and gearbox), port side top - with two wires going to it - worth checking the connections there.

Andy

 

[dlwilkes]

Thank you both for that. It will be something for me to play with when there's no wind... Thanks both again.