Fishing trolley will not STOP

[scooby]

As per the title, on my way to the lake yesterday I was run over by my electric fishing trolley. Suddenly,out of the blue it went full steam ahead, the trouble is i was in front of it, lol. The potentiometer on the handle which controls the speed goes completely round, so the trolley goes to full speed, then stops, then gradually speeds up as it is rotated.
I thought this would be the cause, but i tested the potentiometer and it seems fine, so i unplugged it from the trolley but it still goes full speed! As someone who knows very little about electronics any help would be gratefully received, lol. Will pop some pics on, see if it helps.

Edit ; Forgot to add, i have been unplugging the battery while fishing as sometimes the trolley wouldn't always go at the first time of asking at the end of the day

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[kellys_eye]

Similar in concept to many golf trolleys - probably with a similar end result too (no fish or no hole-in-one)!

Usual fault is the MOSFET(s) go short-circuit. That's the two three-leaded devices (black squares) at the end of the board. Simple to replace.

It 'may' be something else but you can make some simple checks if you have a test meter????

 

[scooby]

Thanks Kelly's eye,
i have a test meter, how do i go about it?

Edit; A little more complex than I thought, but found out which legs were which, found a YouTube video (amen), and provided it was okay to test these in situ, my meter says the gate is closed, so will get a new one and try.

 

[duke37]

The soldering looks a bit blobby on the fets. If the fault is intermittent, then the fets are OK.
If the gate of a fet is not connected to a defined voltage, then the fet can do its own thing and turn on and off with a whim.

 

[scooby]

The soldering looks a bit blobby on the fets. If the fault is intermittent, then the fets are OK.
If the gate of a fet is not connected to a defined voltage, then the fet can do its own thing and turn on and off with a whim.

oops, fat fingers! Thanks duke, the trolley goes full speed as soon as I connect the battery. If I was younger maybe it wouldn't be such a problem, lol.

 

[shrtrnd]

MAKE SURE THE POWER IS DISCONNECTED FOR THIS:
As long as you've got a meter (I assume a digital multimeter). You might want to check that potentiometer in the second picture you posted, just to make sure it's still providing a variable resistance.
Sometimes they crack or otherwise fail internally and give you an electrical 'short' or an 'open' circuit.
If you have a meter that checks 'ohms', put one test lead on one end of the three lugs, and the other lead on the center lug, move the turning shaft and see if the resistance value on the meter goes up and down, or if it doesn't
produce a smooth up and down value. Just one more thing for you to check. If the pot was impacted and damaged, you might see the problem you have. (Although it's a good bet a component or two on the circuit board itself is damaged).

 

[scooby]

MAKE SURE THE POWER IS DISCONNECTED FOR THIS:
As long as you've got a meter (I assume a digital multimeter). You might want to check that potentiometer in the second picture you posted, just to make sure it's still providing a variable resistance.
Sometimes they crack or otherwise fail internally and give you an electrical 'short' or an 'open' circuit.
If you have a meter that checks 'ohms', put one test lead on one end of the three lugs, and the other lead on the center lug, move the turning shaft and see if the resistance value on the meter goes up and down, or if it doesn't
produce a smooth up and down value. Just one more thing for you to check. If the pot was impacted and damaged, you might see the problem you have. (Although it's a good bet a component or two on the circuit board itself is damaged).

Thanks shrtrnd, the pot was the first thing I checked. I got the trolley second hand and soon realised the pot would quite easily go past it's maximum setting and back round again! I thought the motor wouldn't run with it disconnected so was surprised to find it made no difference taking the pot out. Anyway, I tested it as you say and it appears to work smoothly

 

[scooby]

Well, received a new mosfet in the post today and, hey presto, my trolley is running again. Thanks everyone for your input, I'd never have managed it without you!

 

[shrtrnd]

kellys_eye scores again.