TC40DA - hour meter stopped working

[pak7819]

Jinman, you out there? I found a similar thread from 2010 where a guy's tach and hour meter plunked out, you were very knowledgable.

My 2006 TC40DA's hour meter recently stopped working. Tach works just fine. Any advice aside from checking connections on back of gauge cluster? Hope I'm not looking at a new pricy component....

Thanks,
Paul

 

[jinman]

Paul, there is darn little you can do to repair an electrical problem with the hour meter. The Repair Manual shows next to nothing about it; not shown on schematics. The only thing it says is that it is powered from the alternator. That means it should not run if the engine is not running. It's not replaceable as a unit like many other parts. The best thing you can do is to dis-assemble the instrument panel and try to clean/free up the mechanism. It's probably gummed up from condensation over time. Go to this link and look at what is involved in opening up your panel. I was working on my temperature gage, but you'll have to open the panel the same way.

 

[pak7819]

Not the end of the world. I'm not opposed to getting my hands a little dusty. If need be, I'll run an additional hour meter just so i can track maintenance intervals and fuel comsumption. Thanks for the insight!

Paul

 

[Spicer]

I had the same problem.

My repair of the hour meter is out of the scope of this forum, but hopefully I can shed some light. I repaired the hour meter after the coolant temp gage had failed.

If you are not familiar with electronic repairs you shouldn't attempt it. It could cost you several hundred dollars, send it to a professional.

Do not remove the hour meter from the circuit board as shown.

The hour meter runs when there is power applied to the Microprocessor (U3). The MPU send a momentary signal every 36 seconds to the NPN transistor (Q1). This transistor provides a circuit path to ground on the hour meter solenoid. The other end of the solenoid is connected to 12V positive.

On my instrument cluster Q1 had failed. After replacing the transistor I added a schottky free wheeling diode across the hour meter solenoid leads.

Mike

 

[jinman]

So Mike, you think the collapsing field around the solenoid caused your Q1 to fail? I take it that your Schottky diode shorts the field away from Q1.

 

[Spicer]

Yes, and I know that you know that. You just want me to explain it.

A solenoid is an inductor. An inductor is the opposite of a capacitor; it stores energy dynamically vs. statically like a capacitor or battery.

When you apply a current across an inductor the electrons flow through the winding. Since the electrons have mass they do not want to stop flowing when the circuit is opened. Since you cannot create or destroy energy that energy will ring back and forth through the inductor until it finds equilibrium. At this point there could be several thousand volts and it will find the closest path to complete the circuit. The closest path would be the transistor itself.

A freewheeling diode will protect this circuit. A diode will only allow current to flow in one direction. If a diode is connected across the inductor it will shunt the first ring of the inductor. There was already a freewheeling diode (D2) which was a 1n4006. I felt that the forward voltage on this diode was too high and would not adequately catch the first ring.

Mike

 

[jinman]

Well, since the Schottky diode has so much less forward biased junction voltage drop and is so much quicker, it is surely conducting the lion's share of the current from the collapsing field. What intrigues me is that you took the time to analyze the circuit you found by tracing the circuit thru components on the PCB. I have not been able to locate that level of detail on any schematic. The rruth is that I would have probably attempted to reverse engineer that circuit just as you did if I were to have a failure. Nice job!:thumbsup:

BTW: Is U3 on the part that has been removed or just out of the photo?

 

[Spicer]

From the picture you will see that I made a mistake on the disassembly of the hour meter. What appear to be blade terminals on the ends of the wires are actually the wire termination for the hour meter solenoid wires. These terminals should not be removed from the hour meter. The correct procedure would be to unsolder these leads from the back of the board.

The picture below now shows the MPU (U3).

Mike

 

[RobertN]

My TC40D hour meter works fine. But I don't like it... It seems to record hours running. My old Kubota, the hour meter measured time at PTO speed.

I have put 200 hours on my meter, but the old Kubota would have had 2/3 that amount, since most time was spent below PTO speed...

 

[jinman]

My TC40D hour meter works fine. But I don't like it... It seems to record hours running. My old Kubota, the hour meter measured time at PTO speed.

I have put 200 hours on my meter, but the old Kubota would have had 2/3 that amount, since most time was spent below PTO speed...

Robert, I'm not challenging your description of the Kubota hour meter (proof meter), but that seems like a very weird way to mechanize the meter. For example, if it only records at PTO rpm, then I could run at PTO speed minus 100 engine rpm and never put any hours on my tractor. Surely, I'm misunderstanding your description.