Oral-B Fuse Replacement Guide

Yesterday I was connecting my Oral-B Genius to Home Assistant. Once I got it on the dashboard, I started playing with the pressure sensor. Bad idea.

Rather than pressing laterally on the axle, I stopped it from rotating, which I imagined spiked the motor current. Everything slowed down and then halted. Once I pressed again, the motor would spin for about 1 second before giving up. HORROR.

I immediately looked online what could have happened, and luckily I found a few tutorials in video format that pointed to the internal PTC fuse. Phew. The toothbrush is safe.

This page will guide you through the process of replacing the fuse yourself.

A bit of physics to put things into perspective.

When current passes through it, the PTC experiences a phenomenon called thermal expansion. When the temperature reaches a critical point, the conducting particles are pushed too far away. The current cannot find any path to move through the interal non-conductive polymer. The circuit is 'open'.

Guide to fix any Oral-B model toothbrush fuse

Here you can purchase a replacement fuse, you are going to need a 0805 6V 1-1.5A.

Step 1: use a pair of pliers to pull-out the bottom. Pay attention not to break the plastic.

Step 2: pay attention to put the spring back inside at the end of the procedure.

Step 3: an overview of the internal PCB. Notice the square microntroller (MCU) angled by 45 degrees.

Step 4: close-up of my old PTC. You can press it down on the PCB to short it together and test if that was the issue. If so, skip to step 8 to reset the MCU, otherwise keep reading.

Step 5: add some flux to aid with the reflow.

Step 6: clean the solder joints, add more flux if necessary.

Step 7: the new PTC is in! Keep reading to reset the MCU, the motor won't spin just yet.

Step 8: we need to jumper a ground point to a test-point on the PCB. Prepare a set of tweezers so that you can use them as a bridge. A very solid ground point you can use is the motor metal case. Just apply pressure with your fingers to keep in place one end of the cable over the motor.

Step 9: the testpoint is on top of the microcontroller. Touch it with the tweezers to reset the failsafe condition. Pay attention, the motor will start spinning immediately. You can safely turn it off by pressing the power button.

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