A construction worker brought it to my shop. It was a dead battery charger that does not charge the Hitachi power tool batteries for the power drill that he uses for his work. He said that he took it to someone else to get it fixed but the technician only changed the power cord but that did not bring it to life.
Once I opened the cover and scanned the board with my naked eyes, I spotted a resistor that had a black dot on it. It was red black gold and gold. That means it was only 2 ohm resistor and also a fuse. When I measured it with my meter, it was open.
I replaced that with the same exact value and powered the machine. That did not bring the charger back to life.
The main power capacitor was not discharging at all. Even when I unplugged the power source, the capacitor was still holding the 300 dc volt there. To be on the safe side, I had to discharge it before I continue working on this charger.
Later on I found another transistor that was shorted out. The part number was BV42. It is unusual transistor. When I checked the specification on it, it was NPN, 700 volts with 2 amps rating. I could not find one like it in the stores. I checked with some technicians that I know in my area and I was lucky to find one. He had exactly the same charger but with a different problem.
These were the faulty parts that I found in the charger for Panasonic power tool battery. Replacing both the resistor fuse and the transistor brought the battery charger back to life.
To me, it was strange how the guy send it to be repaired and the technician replaced only the cable. It was a guessing work for him. It takes only one minute to find out if the cable is faulty or not. Obviously , the cable was in good conditions because by checking, I was able to find the actual fault with this battery charger. When I checked the original cable that came with it, it was not faulty, it was just dirty and looks old.
Make sure you test things out and not to be fooled with how old or dirty the part look like. Mission accomplished.
This article was prepared for you by Waleed Rishmawi, one of our ‘Master Authors’ and currently working in the Bethlehem area of Palestine repairing electrical and electronic equipment.
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