Thermo Start Light

[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.