Troubleshoot Milwaukee 18V Charger

[vidarr]

My charger for my drills stopped working. I need this thing for work. The voltage coming out is very unstable 5V max on one of the terminal fins. The others are around zero to just a couple volts, also fluctuating. I tested to make sure the AC was coming in and it is. After that, I was just guessing and poking around with the DMM; that lasted 20 mins. I did watch some videos, but nothing was helpful.

All of the components seem to be in good condition visually--- except for a diode that looks odd. There are no signs of anything burning out, or smoke releasing though. I know what all the components are more or less. I just need a jump start on where to begin, or maybe there is something that I should start with after the input/output.

Sorry the pics are bad.

Thank You!

edit: The pictures got rotated in the wrong direction by the website.

[fzabkar]

Can you identify the markings on the ICs on the solder side of the PCB?

[vidarr]

Two of them are legible. The third appears to have no markings. There was a layer of some type of glue dabbed on the top of each one that I carefully scraped off.

F2001
08KG4
ATHNO
(HTSSOP14 ic chip? or IC MCU 16BIT 1K FLASH 14-TSSOP? ---- Brown-out Detect/Reset POR PWM WDT)

D413A
BA1219
(P-Channel MOSFET Transistor)

The third one has 8 pins and looks like a timer. IDK what it actually is though.

THANK YOU!

[fzabkar]

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

MSP430F2001 16MHz MCU with 1KB Flash, 128B SRAM, timer, comparator:
https://www.ti.com/product/MSP430F2001
https://ae01.alicdn.com/kf/HTB1FpgOsxWYBuNjy1zkq6xGGpXa6/50-MSP430F2001IPWR-F2001-MSP430F2001-TSSOP14.jpg (photo)

Maybe this application note would help to visualise the circuit? There is a "Block Level Schematic" on page 3.

Li-Ion Battery Charger Solution Using an MSP430 MCU (Rev. B):
https://www.ti.com/lit/pdf/slaa287

[floobydust]

A common problem with the Milwaukee chargers is the cheapass electrolytic capacitors, the bottom tier CapXon, JWco etc. Like the 10uF, 47uF parts I think.
Just replace them, before you blame the IC's. The brownish glue is known to turn conductive with age, so scrape it off from HV areas.

[vidarr]

I tested the MOSFET and got a reading of 2.05 kΩ
According to a video I watched that means it is bad. It was said the reading should be 700.

Looking at the schematic now.

Looks like testing the MSP430 MCU (08KG4) is quite a task. I see a lot of testing videos with Arduinos; I have one, but not the setup I see being used.

THANK YOU!

[vidarr]

Yeah, I hope it is a capacitor. That is much easier to test and replace. I'll scrape the glue off and test them too.

THANKS!

[Richard Head]

In one of the pictures U101 looks like it's cracked.

[vidarr]

I wish it was that. It is not cracked though; it was glue. It would be so much easier if the broken component(s) would just reveal itself. LOL.

Thanks.

[David Hess]

A common problem with the Milwaukee chargers is the cheapass electrolytic capacitors, the bottom tier CapXon, JWco etc. Like the 10uF, 47uF parts I think.
Just replace them, before you blame the IC's. The brownish glue is known to turn conductive with age, so scrape it off from HV areas.

That is my experience with other chargers.  The smallest electrolytic capacitors tend to dry out first, so replace them before replacing the larger ones.

[vidarr]

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!

[vidarr]

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!

[vidarr]

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.

Thanks.

[magic]

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?)

edit
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?

[vidarr]

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!