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Are your Charging Coil wires broken?

We had a customer email recently here at Ionic Industries. During battery replacement on their Type 3728 Braun Oral-B toothbrush the customer had broken a couple of the 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!

braun-oral-b-3728-professional-care-coil-wires-2Type 3728 Charging Coil Connections

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. To get a good solder connection you might need to scrape the clear insulation off the wires or melt it off using the soldering iron.

Has this helped you? Have you tried it on the Type 4729 or others? Please leave a comment below!

Also see our complete guide to replacing the battery in the Braun Oral-B Type 3728 toothbrush.

17 thoughts on “Are your Charging Coil wires broken?

  1. In the process of replacing the battery on a Braun 4729, one of the charging coil wires has broken off at the point where the wire leaves the charging coil housing. How do I unwind enough wire from the coil to reconnect it? Are the wires glued to the housing?

    Many thanks

    Richard Bush

    1. Hi Richard, if you can’t rejoin the wire you should be able to unwind one turn of wire from the coil to give you enough slack to solder the wire back to the PCB. There might be a blob of glue holding the wires down but if this is “hot glue” you might be able to peel the glue off. Be very careful not to break the other wires though! Let us know how you get on 🙂

    2. I have just fixed my Braun Oral B with exactly this problem. With a big magnifying glass it was possible to see the loose wire on pin 3 . Its a difficult solder but with careful hands you can save a bundle. This was caused by falling off the bathroom shelf into the sink. Be careful when removing the brush head collar and be careful opening the unit using the charger as a spanner.

  2. Great picture saved my bacon two wires broke and wasn’t sure which was which
    Not very easy to solder but sorted in the end with magnifier

    1. Glad it was helpful Delboy!

  3. Hi, many thanks for your drawing. I was in the same situation as Richard above (with a 4729). One of the coil wires got broken and unfortunately it was wire a’ from the coil underneath so I couldn’t unwind just a little bit because the wire was stuck by the coil from the b-b’ wire. Therefore I unwinded both wires completely until I could have the slack I wanted on all wires. I winded everything up again, soldered everything back together (not easy for a beginner!), and the amazing thing is: my toothbrush works again! I must say: I fell in love with the thing after all we went through 🙂

    1. Great work – glad the drawing was useful. Let’s hope you and your brush are together for years to come! 🙂

  4. Hi

    I’ve got a Triumph v2 brush and after replacing the battery and it would not charge I noticed the coil wires broken from each side, the tooth brush does flash to say the battery is low so that’s good. So I’ve unwound all the coil to slacken enough to the right side and rewound the coil back again and got enough for the left side also and this appears to be making contact with the solder blobs it appears to need to touch but when put on charger I get nothing. Can the coil be unwound and rewound? also it there a way of making sure connections are good with solder on the wire? or hot glue gun?

    Thanks in advance and great service you provide.

    1. Hi Jamie, when a coil wire is broken you can unwind a turn of it from the coil and re-solder it to the PCB. If you have rewound the entire coil it shouldn’t make any difference. The main thing is the re-soldering. The wire is coated with a transparent insulating coating which needs to be burned off when soldering. Make sure the tip of your soldering iron comes in contact with the wire when soldering it to the PCB to make sure the clear layer is burnt off.

  5. Quick question: I have a 4735. Is it 4 wires at all times or could there be 3? And by 3, 3 going to the PCB board and not 4? Thank you.

    1. Do you mean a Braun Oral-B Type 4736 toothbrush? On brushes that have 4 wires, two of the wires go to the same PCB pin so there are only 3 PCB pins.

  6. Phew, thanks Ionic, this just saved my $200, 15 year old Braun Oral B Sonic complete, model 4717.

  7. Thanks for sharing! I also have broken wires at home.I will look up some people who are knowledgeable about copper wires to help me. However, I’d like to label broken parts in order to prepare everything right before a specialist comes.

  8. I have a Braun Oral B 5000 series toothbrush. During repair attempt one of the 2 plastic clips on the induction coil assembly witch secure the unit to the housing was broken off. Do you know where I could purchase a new coil and the plastic part on which it is wound?

    1. Sadly, spare parts are not available. You might be able to use glue or hot-glue to repair the broken plastic – it doesn’t have to look pretty! The other alternative is to buy a faulty brush off eBay and use the parts from it.

  9. I had broken coil connections on a 3762. In the process of re-wrapping it, I didn’t realize it had kinked. I broke the copper wire well away from both ends. What are my options for fixing or replacing the coil? Could I possibly purchase bulk wire to replace the whole coil? If so, what would be the specs? It appears to have an outer diameter of 0.0130 inches or 0.33 millimeters, which corresponds most closely to AWG 28 solid wire. However, I see above you say the wire has a transparent insulating coating.

    1. Yes the wire has a transparent insulating coating. The wire you use needs to be suitable for use in coils such as transformers or maybe inductors. Sometimes it is known as magnet wire.

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