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New here and I need help

Tunaman

New Member
OK. Well...not really ok. I just wanted to thank those here that helped me so far. I have installed the new transistors, 22ohm resistor, and the new diode. I get the green light to come on, but the voltage on my power supply drops from 12v to 5.6 and keeps dropping. Usually when a battery is connected it goes from green to red when you first hook it up, then turns green when it is fully charged. The mosfet is still getting VERY hot. These chargers are supposed to put out between 20-23 volts so I dunno what to do now.
 

rjenkinsgb

Well-Known Member
Most Helpful Member
Strange. It sounds like something is shorting either the input or the output..

Can you post photos of the modified unit?
 

Tunaman

New Member
I tried the best I could . No leads or pads are touching. I was going to reflow some of the resistors with the hot air but what is the sense if it doesnt work. Maybe someone can spot something missed. The soldering is a little sloppy sorry for that.
IMG_1125.JPG
IMG_1124.JPG
 

rjenkinsgb

Well-Known Member
Most Helpful Member
I'd not really trust all those surface mount components after they have been removed and refitted; it's a test better done on a freshly-failed board.

It's quite easy for surface mount parts to get damaged by stress when soldered with an iron, as they expand far more than the relatively cold PCB.

One thing you could try is disconnect the FET gate resistor from the transistors and connect it to 0V instead, so the FET is held off?

Then see if it draws any excess current with just power connected. If it does, there are component faults somewhere.

If not, check with your meter on AC for voltage on both the transistor bases and emitters, relative to 0V - you should get a reading from the drive waveform on both if the transistors are working and the IC is producing the drive signal?
 

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