Electronics > Repair

Troubleshoot Milwaukee 18V Charger

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I am pulling all the little capacitors now.

My other concern is if I tested the MOSFET (P) properly. I watched several tutorials and followed the one I thought seemed best for my situation.

Thanks Guys!

I took out all of the capacitors and tested them. They were all good except for one was questionable. I bought new ones anyway.

Am I testing this MOSFET (P) right?

It is: AOD413A 40V P-Channel MOSFET (http://aosmd.com/pdfs/datasheet/AOD413A.pdf)

I watched some videos, but I don't know if what I am getting means it is good or bad.

The diode check seems to be good. I get 0.558V (D+ / S-) and "OL" (S+ / D-).

The resistance tests I am getting "OL" between all pins (no matter what two pins, any which way they can connect).

Thank You!

I have not been able to fix this thing yet. Piece by piece everything I take off and test seems to be OK. I need these drills for work and I won't be able to get a replacement for at least another month.

What happens if I use my 19v laptop charger to charge the 18v battery? This is out of desperation.


If it's a 5 cell Li-ion pack: may charge too fast initially and will not charge it fully.

Proper charger would limit current to full battery charge per 2 hours and limit voltage to cell count times 4.2V. The original charger you have likely communicates with electronics inside the battery to determine capacity and monitor its temperature for signs of trouble. (BTW, any chance that there is a connection problem and the charger can't "read" the battery?)

As for fixing the charger, it seems that there is an optocoupler in it. It likely controls the PWM circuit on the primary. Can you determine what's the current through the input side of the coupler (on the secondary of the PSU)? Maybe there is a series resistor near it or something...

I guess the opto is connected to the MCU?

Is the MCU rail stable and sensible (maybe 3.3V or5V)? How is it powered?

Yeah, I think the optocoupler itself is bad. I tested it onboard and offboard and get nothing. I'm going to replace it along with the new capacitors.
Hopefully this doesn't turn into an exercise of replacing components a few at a time until I find the right one, or combination. Or, maybe just several pieces blew at once. IDK.

The MacGyver laptop charging hack is something I don't want to do, so I put it off for now. I forgot how much corded drills suck though.

Thank You!


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