Tachometer problem on a Jinma 284

jjkane · Oct 3, 2009

The tach on my 284 up and quit a while ago and I am finally getting around to fixing it. I checked the sending unit and it generates approximately 4.5 to 5 volts AC at idle and increases as RPM's are increased. The tach doesn't work at all. My question is what voltage should I expect to see from the sending unit at idle and at a higher RPM?

jjkane

RonMar · Oct 3, 2009

The sending unit isn't really generating a voltage. Well it is as it is a hall effect sensor(coil in core) that reacts to the ring gear teeth passing in close proximity to the sensor. The signal that the tach gauge is reacting to is the frequency change as the pulses become more frequent as the RPM increases. The fact that it is putting out a voltage indicates that the sensor is probably OK, and the gauge is failing to make use of it...

quicksandfarmer · Oct 4, 2009

These sensors are notoriously fickle. As Ron indicated, the tach works on frequency, not voltage, so it's difficult for someone without an oscilloscope to verify operation. The 5V is a good sign though.

The most common problem is that the sensor has moved a little and is too far away from the flywheel. The first step is to make sure that the sensor is close enough to the flywheel, it should be about 1mm. The way to do this is: (with the engine off!) loosen the locknut, screw the sensor in until it touches, and then back it out 3/4 of a turn and tighten the locknut.

The next thing to test is whether that 5V signal is getting all the way to the tach input on the dashboard. If it is, my understanding is that the entire instrument panel needs to be replaced, there is no repair for the tach.

bjr · Oct 5, 2009

Has anyone tried the replacement tachs at Surplus Center? I called once and was told all they had were the heads and no senders/ transducer units? Why would they try to sell incomplete units? bjr

Bob Rooks · Oct 5, 2009

bjr said:
Why would they try to sell incomplete units?

Um, because they are surplus?

studor · Oct 5, 2009

JJ
When mine quit working I ajusted it according to the instructions above and it worked for while longer then quit -- new sensor is cheap and the most likely solution

quicksandfarmer · Oct 5, 2009

studor said:
JJ
When mine quit working I ajusted it according to the instructions above and it worked for while longer then quit -- new sensor is cheap and the most likely solution

I had exactly the same experience, $19.50 plus shipping for a new sensor. I'll also add the that the guys who sell Jinma parts tend to get them to you on the double, I think I had a new sensor in the tractor two days after I ordered it.

jjkane · Oct 5, 2009

Thanks to all who have replied. If I get home early enough one day this week I'll investigate further the wiring to the instrument cluster. I also have a scope I can put on the sender leeds to check for the change in frequency as the PRM's are increased.

Thanks
jjk

jjkane · Oct 12, 2009

Here is an update on the tach problem. I found I was able to disassemble the instrument cluster and seperate the other gagues from the cluster leaving just the hour meter and tach in one piece. There is a board that is most likely the problem. If anyone has any defective cluster panels maybe I can get what I need to get a working set from them. Any help would be appreciated.

Thanks
jjk

Affordable · Oct 13, 2009

Can you send me a pic of what you need,I have a few used cluster panels that have single gauges that did not work,1-had a bad fuel gauge that I have been keeping for parts
tommy@affordabletractorsalesco.com

Tommy
Affordable Tractor Sales
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