Paslode B20543A aka 902661 Li-Ion Battery Charger Repair and bonus battery fix

[GraemeG]

My nephew asked if I would have a look at a couple of faulty Paslode nail gun battery chargers and batteries. He and his friend both had failed units and just for fun added a couple of dead batteries.

The charger is held together with 4 pozidrive screws and is easily opened. The board just lifts out. Both chargers I had used the same revision circuit board labelled PT-244-01 Rev1.3. Here are some photos of what the units and charger PCB look like. We already suspected an intermittent power connector due to flickering LEDs when the power plug was moved on one of the units. Taking a closer look at the PCB under the power socket showed the tracks and pads had lifted and broken away.

[GraemeG]

With one of the chargers, two pads on the power connector had completely lifted and when the socket was unsoldered they both came off. On the second charger only one pad had lifted a little but it had broken the track at one side.

My solution was to glue the connectors to the board with 5 minute epoxy and just to be sure it stayed there I drilled a couple of holes in the board and added a copper loop over the top of the connector and soldered it to the board. I had to do some careful scraping to remove the green solder mask to solder on the copper loop and for the repair to the tracks. On the board with the missing pads I added a couple of short bits of copper wire to bridge the missing copper pads. The photos of the repaired boards are not great but I have included both to show the copper wire bridges on one and the extra solder to reinforce the other. No other faults were found and both chargers now work. Easy!

[GraemeG]

But wait! There's more!!

The 2 batteries that turned up with the chargers were also both "dead". Neither would take a charge and both showed 0 volts on the connector. The centre connector is for a thermistor to monitor the battery temperature during the charge. While running some checks on the repaired chargers I noticed the voltage on the centre connector was about 2.7V on one battery and floating at 5V on the other battery. With the battery off the charger and checking with the multimeter I could measure between the negative and centre connectors about 12Kohms at room temperature on one battery and open circuit on the other.

The batteries are a pain to get apart but I cut a few small strips of thin metal (from a piece of colorbond roofing!) and slipped them under the plastic clips. With some careful levering I managed to get the first battery apart and only broke 2 or 3 of the clips. I was getting pretty good at by then so with the second battery I still broke 2 or 3 clips but it only took a 10th of the time and swearing 

BTW the cells and circuit board are well (seriously well!) glued into the bottom half of the battery case. But if you lever and keep applying pressure it slowly peels the glue away from the case. Start at the end away from the connectors, levering at the sides. Be careful not to damage the cells.

In the photo you can see the small white thermistor taped to one on the cells and in the bottom view I have marked the 2 pads where it is soldered to the PCB. A quick check with the multimeter confirmed one thermistor was open circuit and the other was in the 10-15Kohm range depending on the temperature. To make life interesting, the battery pack with the good thermistor had one dead cell. The good cell was at 4.1V and the other was zero and would not take any charge from my bench power supply. But in the second battery pack the thermistor was open circuit and both cells were at about 2.6V. Promising!

A quick transplant of the good thermistor into the pack with 2 good cells and we were in business.