Unnamed 3 Modes Rotating Electric Toothbrush No operation Fix

Suddenly, my cheap China toothbrush stopped to work. I was operating it nearly 6 months.

Button did nothing, but with Type-C connected it flashing the lights, that means MCU is alive.

To teardown first you have to extract the bottom cap. Try to not damage the sealing resin.

Then push the iron bar (toothbrush output) inside to extract the frame. Be careful: all covered in oil to avoid water dripping inside.

Examine the frame. It contains the engine, PCB, and 14500 battery (not soldered)

First I thought that water dripped inside and caused to components failure, but there was no sign of water, so It's a component failure.

In my case I found that failure was in the CM1125-DWS SOT-23-5 discharge battery protection controller with integrated MOSFET. (I will provide the copy of datasheet to the docs)

All voltages were on place, but inner MOSFET was not opening.

I don't have this controller so I've replaced it with a soldered jumper. Please note that after this, battery charge requirements may become more critical (battery can be overdischarged). It's recommended to replace the battery to 14500 with protector.

Be careful when assembling, the rubber seal must have a good contact with case, otherwise all water will be inside and can damage something else.

Try coating the board parts with silicone sealant before assembly to increase service life.