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Repair: Blown SMD identification problem - Lipo charger/motor driver pcb

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tzaphkiel:
Good morning,

I find myself repairing a shaver with what was to be just a battery replacement. I accidentally inserted the LIPO in reverse polarity and what I suspect to be a protection diode or a cap near the motor blew.
I put here two annotated images: 1) of the whole board, 2) of the component that blew.

It is an SMD component that to me does not look like a diode, it looks more like a cap...
The circuit near the motor looks simple enough: a P-Channel MOSFET, one cap (orange to the right of the MOSFET), a blown component and some control electronics for the charging, switching speed of the motor, etc...

At the moment, I've tried different a diode in reverse bias with my lab supply to power the board with 3.7/4V 1A C.C. (to be safe). The red light lights up supposedly saying the battery is not charged.

I tested the motor separately and it still works. When I flip the switch, the motor twitches and then the red led comes on (batt low or something...).
I believe that even if the blown comp was a diode, the motor should still start turning...
If it is a cap on the other hand, maybe it is to give the initial impulse to the motor to make it turn but then with what cap value should I replace it with ???

Btw, the SMD component had no other markings than what I think is the brand: EDLEN .

Could someone please help me to:
- identify the blown component (SMD)
- possibly point me out to another problem as to why it does not work.
- as I'm a beginner, some pointers to further analyze what is wrong.

Thanks
Tzaphkiel




amyk:
EDLEN? That appears to be a supercapacitor... consistent with it containing liquid (the electrolyte is corrosive, you should clean it off the board as much as possible) as you claim. Diodes do not contain any liquid.

tzaphkiel:

--- Quote from: amyk on March 31, 2013, 10:57:45 am ---EDLEN? That appears to be a supercapacitor... consistent with it containing liquid (the electrolyte is corrosive, you should clean it off the board as much as possible) as you claim. Diodes do not contain any liquid.

--- End quote ---

Thank you, that would make sense... I did clean the board straight away with a short brush and alcohol!

If it is a supercapacitor, why than have two cap in the circuit, one between MOSFET-src/-ve and supercap between MOSFET-drain/-ve ???
How could I identify the capacity? Would a simple cap do ?
So if it is a capacitor, is it to start the motor spinning ?

metalphreak:
That looks more like a diode than a capacitor...

It's across the motor terminals to stop any back EMF from the motor feeding back. Reversing the battery polarity probably let a massive amount of current go through that diode and back through the reverse biased junction in the mosfet. You might find the mosfet is toast as well.

tzaphkiel:

--- Quote from: metalphreak on April 01, 2013, 05:44:04 am ---That looks more like a diode than a capacitor...

It's across the motor terminals to stop any back EMF from the motor feeding back. Reversing the battery polarity probably let a massive amount of current go through that diode and back through the reverse biased junction in the mosfet. You might find the mosfet is toast as well.

--- End quote ---

Yup, well that's what I thought until I saw liquid (electrolyte) coming out of it and after trying with a regular diode in reverse bias... So I'm not too sure about it being a diode.
On the other hand, whether it is a diode or a cap, having had a large current in reverse polarity indeed probably fried the mosfet...
Is there any way to test it ?

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