Thermo Start Light

[Scotty Dive]

I have what I believe is a light that is the thermo start indicator light - mine does not work. I actually thought it was for illuminating the gear shift when the headlights were on.

Can anyone tell me what it is actually for? And - if its the thermostart light - how does it work? In other words, the manual says to hold the key switch to TS to begin the heating process. The light will go off when you are ready to start the tractor. How does the thermostart provide voltage to this light?

 

[winston1]

Scotty, I believe you are correct about that white light. I believe that is just a work light to illuminate the gear shift, etc. My 2002d has one just like yours. It comes on with the light switch.

I do have a red light up higher that did come on when using the thermostart. You can see both lights in the picture. The other picture shows the little black box beside the regulator. My red light did not work when I bought the tractor although the thermostart did work. At one point I took the little black box apart and found something loose. To long ago for my old mind to remember just what. I know I soldered something in there and the light begin working. When holding the key to the left it would come on and go of automatically a few seconds later. Just guessing 10 to 15 seconds. The light has quit again although the thermostart continues to work. The parts manual for my 2002d shows this on the thermostart page with part number 121474-77920. Description comes back as a timer.

 

[Scotty Dive]

Well - thats interesting Winston -

So - I do have a missing light near the the key switch and I do have a similiar black box in the engine compartment - wonder if I am just missing the light?

 

[winston1]

Do you have a parts manual for your 2020? If so, check the thermostart page.

 

[winston1]

I went out and looked at my black box. I can make out WI1-07 and Japan. It has three wires coming off of it. Red, black, and yellow.

 

[Scotty Dive]

Winston - Looks like I have the same black box. I did not remove it but saw no numbers on it. Wonder if it works??? Any idea what I should expect in terms of voltage across those wires? BTW, it does show up in the schematic too. I haven't had a chance to look at the wiring schematic but those are in Japanese so its kind of tough figuring it out. It will be easier to see what wires are behind the ignition switch where that thermostart light would live.

 

[winston1]

As I stated, my light is not working right now. I went out and tested with black test probe to a ground. Red to wires. There is no voltage at any of the wires until the switch is turned to the thermostart position. Then there is 11.27 volts at both the red and yellow wires. Nothing on the blue wire. I held it in that position for at least 20 seconds and nothing changed. That sort of indicated to me it is not working correctly. The thermostart element heated up, by the time I turned it off the manifold was good and warm at that point. I did have 12.6+ battery voltage.

When I get adequate time I may take my box off and take another look in it. I'll try to remember to snap a picture of the innards.

 

[Scotty Dive]

Thanks Winston. I had a few minutes today while it was still warm enough to be outside...I did some digging under my dash - mine is covered with panels and was hoping to find a bare wire with a plug where the TS light would be - no luck....but just for grins I looked up on the opposite side and I could just barely see a bulb tucked way up behind more wires....I fished it out and pulled it over the steering column and it clearly is the TS light. Bulb is still good but it does not light up. Still trying to figure out how it stickes out through the empty hole in the dash as its way to big and I am clearly missing the red lens too. TS does work and heats up in the intake. I even got curious and removed the black box (no numbers anywhere on it) and popped the top to peer in. I have no idea what I am looking at when it comes to circuit boards, but nothing looked broken.

 

[Neat 1500]

I imagine it would go like this - RED is supply from TS position
BLACK is earth
YELLOW is timed supply to lamp which should extinguish after xx seconds.

As it does not actually drive the TS plug i dont know why they went that way in designing it?

 

[winston1]

Here is a shot of the other side of the circuit board. Pretty sure our boxes are identical. You might be able to see where I soldered the middle post on the little black box in the upper right corner. It went to working for awhile but has since quit. It is all over my head now as I don't see anything physically loose or broken.

 

[Roonabeck]

Usually the unreliable component that's most likely to stop working over time is a capacitor. Sometimes they explode which makes it easy to identify the problem part, but they can go bad without any obvious indication also. You could try de-soldering the two capacitors on the board and replace them with new capacitors of the same capacitance (measured in farads (F) or likely in this case microfarads (uF)). That's almost certainly more trouble than it's worth though, if the thermostart itself is still working fine.

The little black box you soldered the middle leg of looks like a transistor, large enough to supply current to power something (possibly a light bulb).

 

[winston1]

Roonabeck, you must be an electrical engineer. I wish I had a better understanding of electrical systems. You are right, after another inspection of my timer box I could see nothing physically wrong so I put it back together and will be satisfied that my thermostart works. Thanks for you comments.

 

[California]

The little black box you soldered the middle leg of looks like a transistor, large enough to supply current to power something (possibly a light bulb).

It looks a little cooked.

I see C1881 K and the Hitachi logo on it. So maybe its this one:

2SC1881K datasheet pdf datenblatt - Hitachi Semiconductor - Silicon NPN Triple Diffused ::: ALLDATASHEET :::

Take a look at the six HTML pages referenced from that link.

 

[winston1]

It looks a little cooked.

I see C1881 K and the Hitachi logo on it. So maybe its this one:

2SC1881K datasheet pdf datenblatt - Hitachi Semiconductor - Silicon NPN Triple Diffused ::: ALLDATASHEET :::

Your a amazing California. I do believe that is indeed the part. A little research shows I could buy a package of 2 for $1.78. Two problems, I don't know for sure that is the problem and biggest problem is I don't think I could successfully remove and install one on that circuit board.

 

[California]

Maybe take it to a TV repair shop? An electronics tech will have a small soldering iron that includes a suction attachment for getting the old part out without overheating the board. He could also analyze if the other components are working properly for the box overall to function as a timer.

You might also look beyond the black box to see what overloaded that component. Maybe a dead short at the lamp. Or maybe the box is designed to time the lamp only, but it was mis-wired to carry the full load of the Thermostart heating element. Does the output of this timer run to a high-current relay which powers the TS?

If the box only times the light and not the TS - I might ignore it. The earlier Yanmars had just an instruction in the manual: 'in cold weather use the TS for a few seconds'.

 

[winston1]

Unusual for me, but I started thinking today about the bulb possibly being bad. I usually try to check out the unlikely first and then proceed to the likely. Although the filament in the bulb looks good I do not get any ohm reading across it. Should I?

 

[Scotty Dive]

Not sure about ohms, but I use the continuity setting across the bulb - thats where the volt meter makes an audible sound when a circuit is present

 

[Roonabeck]

It looks a little cooked.

The only thing I saw that looked a little off in his picture was one of the leads on a diode (labelled "ZD2" I think) looked blue, as if it had become too hot at some point.

Your suggestion to visit a TV repair shop is a good one, although I'm not aware of many of those existing any more around here. You might also try a local makerspace. Someone there might find it interesting to debug a 30-year old tractor circuit board, or might be willing to teach you how to do it yourself.

Although the filament in the bulb looks good I do not get any ohm reading across it. Should I?

Not sure about ohms, but I use the continuity setting across the bulb - thats where the volt meter makes an audible sound when a circuit is present

Zero ohms means continuity, and yes both indicate that the bulb itself is not burned out.

 

[California]

Although the filament in the bulb looks good I do not get any ohm reading across it. Should I?

Should be some very low number of ohms, maybe a fraction of an ohm. (Somebody verify this - I didn't understand Ohm's Law clearly 55 years ago in shop class and haven't thought about it much since. )

That's after removing the bulb. You can't measure it in-circuit because that may also measure other circuit components at the same time - resolving nothing.

A simpler test is remove the bulb and put 12 volts across it. Look at the bulb carefully and be sure it says '12V' before doing this!

 

[California]

You might also try a local makerspace

only thing I saw that looked a little off in his picture was one of the leads on a diode (labelled "ZD2" I think) looked blue

Wow. So thats what kids and hardware-heads are up to in the present century. Fascinating!

You're probably right, more likely ZD2 (or D1) which show some bluing, and are sensitive components. The bubbling on the IC could just be the lacquer visible everywhere on the board. An electronics bench tech would know in a couple of minutes of testing.