**Edited 1/18/10 - Additions at bottom**
I had purchased a used, working well, Bantam BC6 battery charger/discharger/analyzer... quite a fancy & high-tech unit if I do say so myself.
Well about 3 weeks ago when I was doing a multiple charge-discharge test on a battery pack, as part of the discharge cycle, the unit beeped, stopped the discharge, and displayed "Break Down" on the screen. Looking that up on the bantam website and/or related forums, the recommendation is that this thing should be sent back to Korea for repair... not happenin.
So, what I assumed, is that the main heat-source in that whole unit was a transistor labeled IRFZ44N, and that it had somehow gone bad.
On ebay I typed in that part number and got a package of 5 coming this way.
With a few minutes of soldering activity I had the old, dead transistor removed from the board, and soldered in the new IRFZ44N transistor.
IT WORKS! ^_^
What to do & What to look for:
Disassembly - something like 5 screws located on the right-hand face(side where positive & negative charging cables and li-ion charging interface come out from) need to be removed and then the bottom of the unit can be slid out from the rest of the case. After the bottom is removed, you should notice two similar looking objects sticking up from the bottom of the board... these are both transistors. One is a 5 Volt voltage regulator which is located towards the center of the board. The other is THE transistor that you are looking for, the IRFZ44N - it is located near the circuit board edge and is closest to the panel you unscrewed first(assuming you unscrewed the right panel).
Orientation is critical in the re-installation/soldering of the new transistor... the back & shiny face of the transistor should be towards the black/negative charging receptacle; the black & bulging side of the transistor should be towards the red/positive charging receptacle.
Once the bottom is slid back over the newly installed transistor, try to make certain that the back of the transistor is in contact with the blue-ish thermal pad, and that is in contact with the metal case bottom after you slide it back in.... that is this transistors only way to dissapate the heat.
If this transistor fails and the unit breaks down again, I can picture myself setting up a more active method for cooling it... a fan or larger heatsink or something.
**1/18/10 Edit Addition**
Well it was initially embarrassing to discover that although the BC6 appeared to be functioning flawlessly, given a full day of discharging a battery pack... it was obvious that it was not discharging the pack(the voltage never dropped).
With a little Ohm-meter testing it was discovered that a 0.5 Ohm resistor which connects to one of the legs of the IRFZ44N burnt out; the resistor was reading over 10,000 Ohms. The resistor which burned out had R500 on it, and after testing the two R100 resistors next to it with an Ohm-meter and finding out that they are 0.1 Ohms, I made the assumption that the R500 should be
The picture shows the location of the burnt out .5 Ohm resistor(circled in yellow - right side of picture) and the part number & specs of the mouser-ordered replacement part(yellow rectangle around the area).
The dimensions of the resistor(original one and the one I replaced it with) are: .125" x .25"; the height doesn't really matter much, but it was .065" or less. The printed label on the new resistor is R50F - not that it matters that much, the 0.5 Ohms and 1 Watt power handling matter more than the label.
Since I haven't invested in any desolder tools, I ended up using two soldering irons, at once, to melt the solder on both sides of the dead resistor and get it off the board before things cooled.
Now, and with a few days of testing for verifications purposes, I can say the new 0.5 Ohm resistor has allowed this very useful BC6 battery analyzer to function like it originally did and always should.
Here's a picture of the original R500 resistor...