Mystery Part

A picture that shows (almost) nothing..........

Try to heat it up while measuring the resistance (standard ohm meter, at low current), it could well be an NTC for thermal sensing.

A surge protector (Varistor) would be very high impedance at an ohms test, and normally uses thick PCB traces.

Arie

Does the enclosure for this board happen to have an FCC ID# on it anywhere? If so, you might search the FCC's Equipment Authorization database and see if it's listed there. If it is, that's where you'll find photos of the original (undamaged) board, User Manuals, and "sometimes" a parts lists.

Otherwise, hard to tell from your photo, but I don't recognize the part. Good luck!

Thanks for the suggestion but I don't think it likely, its resistance only changed very little when heated up with with 1.2W, and why would they have two of them, quite close together on the same board ?

MK

My pals didn't bring me the box, but I doubt if it will be FCC registered since we are in SW Scotland here (and it's quite old). I'll ask them.

MK

Hard to tell from pic. Any numbers/ letters on it? Two leads? Did you take one lead off to measure resistance? measure an I/V? Some zener diode... maybe back to back...

George H.

What is the make and model of the tractor? Surely you can figure that much out.

Indeed, the photo needs to be in better focus and taken closer to the part, the resolution doesn't support enlargement.

Scottish or UK tractor? Where was it made? Parts seem standard enough, id numbers are not scrubbed off or buried in epoxy.

Might it be an inductor/choke? Do you have a way to test Micro-Henries?

John :-#(#

Did you make those measuremnts in-circuit or did you unsolder it - just wondering if there were sneak paths involved?

Did you try both polarities - just wondering if semi-conductor based?

Can you try substituting from one board to the other?

piglet

Terrible photo. Can you get something better, preferably closer and from two angles?

My guess(tm) is that it's the carred remains of a tantatalum capacitor. The "blackish gunk" if overheated conformal compound (urethane, epoxy, or acrylic) that was used to coat and waterproof the printed circuit board. Look for other parts on the PCB which might be similar to the remains:

It might be useful to disconnect the mystery part, apply power, and measure the voltage across the connections on the PCB. If it's close to the applied or regulated power supply voltage, it might be a (tantalum) power supply filtering capacitor. If it is a filtering cap, the PTO might function with the filter capacitor removed, as in its present condition, might be shorting the power supply to ground (the blue lead appears to be ground).

It's also possible that it's the remains of the rubber plug found on the base of an aluminum electrolytic capacitor. The cylindrical shape of the hard black gunk might be burned rubber. This usually leaves a black or brown mess on the PCB or inside enclosure which seems to be absent. Ask the owner if there was any oily paper, aluminum foil, or a small aluminum can, in the enclosure when he removed the PCB from the enclosure. Also, determine if the PCB or enclosure was cleaned to remove a black stain. It's difficult to tell from the photo, but there does seem to be a blob of clear something directly under the mystery part.

Good luck.

I measured the good one (ie not broken) in circuit - I don't want to risk removing it because the other one was so obviously fragile.

My measurements on the cylindrical blob that was the other one were out of circuit. It's not polarised.

I didn't make clear that the cylindrical body of the broken one is a moulded or machined cylinder with smooth faces - it is most definitely not the charred remains of some larger part.

No spare boards.

MK

Have now got detail from outside of box:

John Deere AL150447 Siemens 5WK10510A

Google on these gets you some hits but nothing useful.

I guess this one is too old for FCC ID.

Thanks anyway.

MK

Thanks. I still have no clue to help you. Are the leads exitting axially (like a 1N4148) or along one side (like an old style tubular cap)?

What else distinguishes the "bad" one from the "good" one - from what I read upstream looks like they both measure 150-180ohms?

Is it this mystery part that stops the board working or could the fault be somewhere else?

piglet

Here are some better pictures, in two of them the "works" from the broken one are sitting on the board between its leads and the unbroken one.

Yes, both measure like resistors.

In real life the cylindrical inside of the broken part looks a lot blacker than the picture.

MK

Thanks, much clearer pics. I have some thermistors in my junk box that look just like that, perhaps exploring their resistance vs temperature behaviour may help resolve.

piglet

Checkout Epcos or TDK - could be like this ...

piglet

Siemens type 382 and Schurter type MST fuses are in a radial case similar to what is described. Now distributed through Littelfuse.

Inductors and thermistors were also fabricated, at one time, in a similar housing.

The case is intended to be flame/explosion proof.

If the flat part of the lead sticking out of the board is soft metal with a punched rivet, rather than a spot weld, it's the terminals of an electrolytic capacitor. I'm not sure those are parts of the component that you're inquiring about.

RL

I think I can read "PTC 420" on the end of the device in the first image.

John

Or maybe 430.