We had a customer email recently here at Ionic Industries. During battery replacement on their Type 3728 Braun Oral-B toothbrush the customer had a couple of broken copper wires from the charging coil where they connect to the PCB. Using the Type 3728 toothbrush we have for testing we were able to identify the connections for the 4 coil wires and quickly write some instructions for repairing the wiring connections. See below for a copy of the instructions we sent!
Take a look at the photo and hand-drawn sketch of the wiring connections above. You see in the photo where the four copper wires go into the white cap containing the coils of wire? Two wires go in and turn left. The other two go in and turn right.
Let’s call the two that turn left a’ and b’ (a-dash and b-dash). We’ll call the two that turn right a and b
With all four wires disconnected from the PCB you can use a continuity meter to identify the wires and label them using some tiny strips of masking tape or similar:
Wire a and wire a’ are the same wire wound into a coil. Let’s call that coil A.
Wire b and wire b’ are the same wire wound into a coil (coil B) in the same direction as coil A but not electrically connected to coil A.
Pick one of the wires that turns right. Let’s label that as wire a
Using the continuity meter find wire a’ because you should get continuity between a and a’. Label wire a’
The other wire that turns right is b so label it it as wire b
You should also get continuity between b and b’. Label wire b’
It’s important that both a and b are the wires that turn right in the cap.
Now look at the photo again and the PCB with the 3 pins that the copper wires connect to. Let’s label the PCB pins left to right with numbers 1, 2 and 3.
The wires are connected to the PCB as follows:
PCB pin 1 – wire a’
PCB pin 2 – wire a AND wire b’
PCB pin 3 – wire b
Solder the correct wires back onto each PCB pin and your brush should charge correctly again.
Has this helped you? Have you tried it on the Type 4729 or others? Please leave a comment below!