The tach on my 2007 yanmar has stopped working. I've taken the tach out of the housing and wacked it a few times but to no avail. I'm not sure where the sending unit is located on this engine. I see nothing on the flywheel housing. Any ideas?
3ym20 tach problem
- Thread starter brettgrant
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I know for sure 3YM30 tach has problem. Owners reported high alternator voltage would cause the tach to either drop to zero or max. Maybe your 3YM20 has same problem. One suggested solution is to drop the voltage by some (maybe 0.3-0.6V).
I had the yard check it and they say it is the tachometer itself that's broken. I had one supplier check with Yanmar and they were told there is not one in the whole country. Hard to believe but that's what Yanmar told the boatyard also.
Don't mess with the alternator voltage
Doing so will leave your batteries less than fully charged.
The tack plugs into the unrectified side of the alternator (tach terminal). The frequency of the AC varies with engine RPM. The tach is just a frequency meter calibrated to read RPM.
Take the tack sensing wire off the back, start the engine as see if you have AC voltage between it and ground. You should get 3-4 volts if memory serves. the alternator actually puts out 3 phase so there are 3 AC voltage curves all adding together. The resulting ripple is mostly dc with an AC ripple of just a few volts.
Hey wait! Aren't 99.44% of all electrical problems on boats caused by corrosion? Perhaps you should check all the connections first before you go diagnosing further.
Doing so will leave your batteries less than fully charged.
The tack plugs into the unrectified side of the alternator (tach terminal). The frequency of the AC varies with engine RPM. The tach is just a frequency meter calibrated to read RPM.
Take the tack sensing wire off the back, start the engine as see if you have AC voltage between it and ground. You should get 3-4 volts if memory serves. the alternator actually puts out 3 phase so there are 3 AC voltage curves all adding together. The resulting ripple is mostly dc with an AC ripple of just a few volts.
Hey wait! Aren't 99.44% of all electrical problems on boats caused by corrosion? Perhaps you should check all the connections first before you go diagnosing further.
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