Yanmar 2GM20F Tachometer troubleshooting

[ChuckA]

My tach stopped working. The engine is running fine. Reading the service manual, I checked for voltage at the red/black leads to the tach and found none (should have ~12 V with key on). I traced the red wire back to the switch on the instrument panel. There is no voltage at the switch terminal (# 15 on the drawing) which is supposed to supply voltage to the tach. I'm looking for a schematic for the switch on instrument panel or suggestions on where to look for an open circuit.


yanmar instrument panel_1 by chuckanastasia, on Flickr


yanmar instrument panel_expl_1 by chuckanastasia, on Flickr

[Captainmeme]

I did find a service manual in pdf format on the web. Hold one,.........ahh,
j30.us/files/yanmar-manual.pdf
Take a look towards the end of the manual, there is a diagram showing the tach wiring.

[rikhall]

All of the times that my Yanmar tach quit working it was because some idiot (usually me) had bumped the wires on the engine and one had come loose.

Start simple and go from there.

Rik

[mm2187]

If that panel is the same as my engine the toggle switch you are talking about only allows you to illuminate the tach and to allow you to test the alarm. It has nothing to do with powering the tachometer.

[imagine2frolic]

I have the same panel with a 3GM30F, and my problem has been a loose wire on the sender at the back of the block........i2f

[ChuckA]

Thanks Captainmeme, that's a helpful manual. Here is the schematic from p 56. Now I see where I went wrong. This is from the trouble shooting guide I was looking at from a Yanmar workshop manual.

Tachometer Gauge
To check the tachometer gauge unit, proceed as follows:
1. Disconnect the red/black and black wire leads from the
tachometer. With the key switch ON, measure the voltage
betWeen the two wires. There should be 10-16 volts (battery
voltage). If not, detennine the cause.
2. Disconnect the orange and blue/red wire leads from
the tachometer. Run the engine. Measure the alternating
current voltage between the orange and blue/red wire
leads. The voltage reading should be at least one volt.
3. If the voltage reading in Step 2 is less than one volt,
check the wires and connections and check the sender as
described in the preceding section.
4. If the voltage readings in Steps 1 and 2 are satisfactory,
replace the tachometer.

I confused the red/black for the bulb with the red and black leads. I'll check it again in the morning.


wiring diagram_1 by chuckanastasia, on Flickr

I appreciate the help!

[MY36]

I have a similar problem with my Yanmar 3JH3E. Can anyone tell me where the rpm sensor is on the engine? Is it flywheel driven?

Lawrence

[RichH]

Carefully look for corrosion on the tach sending unit at the bellhousing/flywheel and all the connectors on this entire circuit. Yanmar still uses non-tinned wire on its control panels and the tack sending unit (and the starter solenoid) wire connectors are quite vulnerable. Physically look at the connector as a multimeter reading when the connector is still 'wetted' by the atmospheric moisture will provide (some) continuity ... let it dry out by engine heating and the corrosion will show as an 'open'.

[ChuckA]

Lawrence: The tach sender is on the flywheel housing near the transmission.


Yanmar 2GM20F tach sender by chuckanastasia, on Flickr

[MY36]

Thanks RichH and ChuckA - especially for the picture. I'll start limbering
up for the contortions I'll have to go into to get at it this weekend.

Lawrence