turnigy accucel 8150 old charger repair

[whatever]

so I have to test the irf4905 P-chanel mosfet I took out before puting it back, which means the method using lightglobe and battery has to be changed for P-chanel fet, pics below show the changes
( also will put in new thread on mosfet testing as is handy method for testing fets, very quick also if you have little circuit or breadboard setup).
Using 12v battery with 12v lightglobe no resistor needed in this method:



using led to test mosfets requires resistor 1k in size in series with led globe, I will test with 9v battery also, would make for compact test unit


Although I posted this method back in 2010 ( idea from Warwick Smith from Numurkah secondary school...that guy is absolutely brilliant, not sure what he is doing these days on this forum for 12v testing link to that here:
https://endless-sphere.com/forums/viewtopic.php?t=19585
I went searching for info on P-chanel fets, and came across a really nice video that shows breadboard version for N and P chanel. Its an amazingly simple setup. Also in his comments section someone suggests if using a wire instead of your hand to turn on/off the fet ( via the gate leg) that a resistor should be used on that wire also. Some of the comments are worth a read on this vid:
[youtube]https://www.youtube.com/watch?v=p-PouEtYbns[/youtube]

 

[whatever]

anyone who is interested in a fairly comprehensive explanation of the how these types of boards work, and how the components work together can see this video, at the 22min mark approx, he brings up circuit diagram for a 6s version of similar board, and explains quite a bit of detail using the circuit diagrams.
[youtube]https://www.youtube.com/watch?v=3LfU4mjgpyM[/youtube]

 

[whatever]

Tested irf4905 P chanel fet that I took out of the board, and it works fine. So re-installed it where I put incorrect type fet, tested the unit, at 0.3amp charge current on 24v nom pack the inductor was once again getting hot.
So just trying to nut out what the issue is, the inductor did get very hot previously, so thinking maybe the inductance is not correct,
but really not sure what the problem is.
so went to the circuit diagram previously mentioned, dia below shaded out components not relevant at this stage, just looking at the charging circuit on right, have labelled the bits in case anyone else goes down same path.

It shows the buck/boost part of circuit ( I think that is the function of this part) with relevant components involved with inductor,
mosfets labelled with their position on the board from left to right, the two fets involved are the 4th from left ( z44n) and 6th from left ( irf4905), D2 and D3 are the to-220 schottkey diodes. And L1 the inductor coil.

 

[whatever]

I'll add some detailed circuit pics and specs just for future reference.
Will be labelled to match any circuit diagrams such as in last post. Fairly high res can zoom in and read values,
any values in white not on top of components are my measurements of resistance/capacitance etc, of components in situ.

 

[whatever]

so have ordered lm2904 chip, there is a slight blemish on its surface, which may or may not be a burn mark, that part has now arrived so will instal it and test charger again see if the inductor coil gets hot again............haven't given up just yet
pic of the possible burned lm2904 below, only changing this part not because I understand what it does, simply due to possible burn mark on its surface.

 

[whatever]

my first time removing 8 leg chip, managed to damage some traces on the board, repairs on hold till I remedy the situation,
may or may not get back to this project.

 

[Monteiro]

Hello all
I'm new here on the forum. My turnigy accucell 8150 charger smoked and stopped working, It was disassembled, apparently only this component of the photo is burned. Can anyone say what this component is? Many thanks in advance. Humberto