Guidance on replacing an unknown part for a multi charger - Page 1
Forum section: electronics / repair

author: Atom_slayer
author_rank: Newbie
timestamp: October 21, 2020, 09:00:31 pm
content: I have a friend who plugged the power cord backwards (reverse polarity) into his Imax c6 multi-charger and released the magic smoke. (Really him, not me!) He knows I like to play with electronics so he gave it to me to repair. He already replaced it, so it is not a big deal if I don't get it fixed.There is a bubble on a component close to where power comes into the board so I assume this is why it's not working. The part bubbled up so it is impossible to see what part number it is. This is a generic charger made in China so there are no schematics to look at and determine what part it is. There are several different brands of chargers that are very similar so I'm pretty sure that most of the multi-chargers are manufactured by the same company.I have a multi-charger is close in appearance and function to the bad charger so I took mine apart to compare the pc boards. There is a part on the good charger that has the same footprint in a similar location as the bad board. Also there are three resistors with the same values in a similar location on both boards, so I am going to hazard a guess and say that the bad part in the bad charger in the same location is the same part in the good charger. The part number of the chip on the good charger is 4407, EA9U1K. Looking at the part number, I think it is a mosfet. It has the same number of pins in the same footprint. Also the part in both boards has the same configuration; pins 1,2,3 are all connected together, 4 is on a separate path going elsewhere and 5,6,7,8 pins are all connected. After looking at that, I am more convinced that it is the same part. I am choosing the 30 volt mosfet since I assume the higher voltage seems to be safer than the 5 volt mosfet.My question is whether you agree with my thinking on this part, or am I missing anything or not looking at ir right.There are three resistors next to the bad mosfet. The two left resistors look fine, but the far right resistor looked like it was smoked. Using my multimeter, the resistance is spot on so I think the resistor is still good. . The resistor on the good charger board has the same value as the resistor on the bad board, so I know what value to get.Question 2. Should I remove the bad looking resistor and replace it with a new resistor? My thinking is that if it ain't broke, don't fix it. I am on the fence on whether to replace it or not.I measured the resistor with a caliper and came up with 2.5 mm which makes me think it is a 1008 smd resistor. When I order my mosfet, I plan to order the resistor as well in case I need to replace the old one.I have included 3 pictures; one of the bad board, one of the good board, and one with a flashlight behind the pc board to look at the traces. When I first looked at the third picture, it appeared that some of the traces were broken. Upon further review, I discovered that what appeared to be bad traces was the white outline of the parts. It looks like the traces are intact .I can replace these components for less than a buck (not including shipping) so money isn't a problem.This is really a learning experience. If it works, great; if not, in the trash it goes and I'm out a couple of bucks.Please bear with me. I am low level electronic hobbyist without formal electronic knowledge but have a keen interest in electronics. Thank you for reading this long problem and I look forward to your comments.

author: fzabkar
author_rank: Super Contributor
timestamp: October 21, 2020, 11:01:52 pm
content: AO4407, Alpha & Omega, P-Channel MOSFET, -30V, -12A, 13mOhm Rdson, SOIC-8:http://aosmd.com/pdfs/datasheet/AO4407.pdf

author: Atom_slayer
author_rank: Newbie
timestamp: October 21, 2020, 11:26:51 pm
content: Thanks for your response. I guess you agree with me on what the part is. Do you think I need to pull the resistor and replace it?

author: fzabkar
author_rank: Super Contributor
timestamp: October 22, 2020, 12:34:35 am
content: I would draw a circuit diagram of the affected part of the circuit. I would also measure the resistance between ground and drain, and ground and source.