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You may find that when you press the trigger the motor doesn't turn. It may just give a little tick and the front light may flash briefly. With the direction switch in the middle (off) position, the front light lights normally.

This is due to the internal resistance of the battery increasing as it ages, even though it may still have plenty of capacity. The initial surge as the motor starts causes the battery voltage to instantaneously drop below the fully discharged voltage. As a result, IC1 disables the motor.

The simple fix is to replace the battery with a brand new one, preferably of higher quality, though the quality of lithium batteries you might find for sale is hard to judge.

The alternative is a modification to the circuit to prevent the dip in voltage reaching IC1. You will need a surface mount 2.2k resistor and a surface mount 100μF tantalum capacitor.

Remove R7 and replace with the 2.2k resistor. Remove C2 and replace with the 100μF tantalum capacitor. The end with the bar on it should be away from the board edge.

The tantalum capacitor will be considerably larger than the one you are replacing and so scrape away a little of the solder resist close to the board edge in order to make a new solder pad. Alternatively, use a wire-ended electrolytic capacitor. Positioned carefully on the other side of the board it should still fit within the screwdriver case.

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