Garden tractor dash question for calibrating air core gauges.

Thread Starter

Eversr007

Joined Apr 10, 2016
40
Ok so Im working on a dash for a garden tractor for a guy and it had a bunch of cracked solder joints on the pins of the connector. I fixed them and need to be able to power it up and calibrate the needles for the two gauges on it. They are only 3 pins on the gauge motors. My question is how do these motors function? Do they run off a variable voltage or is it a signal. Thanks if anyone could help. I will attach a couple photos of the board front and back.IMG_4753.jpgIMG_4751.jpg
 

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wayneh

Joined Sep 9, 2010
16,399
Do they run off a variable voltage or is it a signal.
My guess is the former, an analog current, rather than ay sort of digital signal. Are you thinking to tweak the resistors near them to calibrate them, or to make some mechanical adjustment? I'd be reluctant to mess with them at all unless they were way off.
 

JohnInTX

Joined Jun 26, 2012
4,281
@wayneh is right. These have two analog coils arranged at 90 degrees. The needle is rotated by applying current as the sin of the input to one coil and cosine of the input to the other. 2 coils, one common.
This has some info on how they work:
https://en.wikipedia.org/wiki/Air_core_gauge
The CS289 (DC input) and CS8190 (frequency input) are examples of analog drivers. The sin-cos signals can also be generated by a microcontroller using DACs, PWMs and the like.

All things being equal, if the motor and driver is OK, the calibration is typically done on the front end before any sin/cos driver i.e. scale the voltage applied to the driver and let it drive the needle to the proper angle. Your board looks like the driver / scaling electronics is elsewhere. Calibration would usually be done there.

Not sure what the resistor across the two coils is for. Damping maybe but I wouldn't think calibration...

Good luck!
 

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Thread Starter

Eversr007

Joined Apr 10, 2016
40
Ok yeah so what I was trying to do is apply the analog signal of what the guage would be at its lowest point so I could put the needles back on the instrument cluster at the correct place. And then maybe increase the signal to make the gauge sweep to test that it works at all points. So when they plug it into the garden tractor the gauge will point in the right place. What would I have to get to set this up. Like on a car I run the instrument cluster and test it from a automotive scan tool.
 

jpanhalt

Joined Jan 18, 2008
10,219
You make a key point: needle position.

The one I have actually gotten into to fix actually just had a lose needle. It was the temp gauge from a small (45 HP) tractor. Drove me wild, because it would indicate cold at starting, but then go red high very quickly. Checked everything, then simply put a VOM in the circuit and drove it like that until a new gauge arrived. Put the new gauge in, and it read as expected. Opened the old one up only to have the needle fall onto my bench. I believe that style is otherwise quite robust. A dab of glue would have saved me $$.
 

Thread Starter

Eversr007

Joined Apr 10, 2016
40
Ok so I got all the bulbs to work when hooked up. I attached wiring diagram for cluster if anyone would be so kind to help me figure out how to test the gauges. I could be wrong but they don't look like they are air core motors. The Diagram shows a positive battery voltage and one negative pin and the third goes to sense or sending unit. So shouldn't that be easy to hook up? Also still working on hour meter that doesn't come on but from what I read a lot of them don't work either. Im struggling with this one. Thanks for any help
 

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debe

Joined Sep 21, 2010
1,185
Ok so I got all the bulbs to work when hooked up. I attached wiring diagram for cluster if anyone would be so kind to help me figure out how to test the gauges. I could be wrong but they don't look like they are air core motors. The Diagram shows a positive battery voltage and one negative pin and the third goes to sense or sending unit. So shouldn't that be easy to hook up? Also still working on hour meter that doesn't come on but from what I read a lot of them don't work either. Im struggling with this one. Thanks for any help
The Coolant temp & Fuel senders are variable resistance to ground. You need to work out what the resistance is for a given indication. Some workshop manuals give the readings. Your manual at least gives the fuel level readings of 3 to115 Ohms. The temperature sensor will be a NTC type resistance.
 
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Thread Starter

Eversr007

Joined Apr 10, 2016
40
Thanks for the info. I couldn't get it until I reflowed some more spots on the board. I ended up just doing every single joint on the board. Bad thing is I got the motors to work but one would barely move and the other would move decent when grounded and didn't want to move the other way very easy. And I found the data sheet for the hour meter and took it off board and power it up and its dead to. But I can order a replacement one of those for $40. Would anyone have any idea of where I could purchase these two gauge motors or what they are called so I can search for them. Otherwise I would need to find another cluster for parts I guess. This cluster goes for $797 new to replace it. Thanks everyone
 
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