Braun Series 7 Shaver Repair/Reverse Engineer - Page 1
Forum section: electronics / repair

author: InvncibilityCloak
author_rank: Newbie
timestamp: September 01, 2025, 05:45:32 am
content: I have a Braun Series 7 shaver I use daily. About 9 months after purchase, it "died" so I sent it in under warranty. Now it died again, but no warranty coverage so I figured I would take a look inside. My suspicion was that the inrush current of the DC motor and the battery at a low charge state is triggering the undervoltage protection somewhere.The build of the device is actually extremely repairable. One screw and the outer case slides (no clips!) right off. 5 more screws and the waterproof assembly comes apart. The circuit board isnt even soldered on - there are clips holding it down and making the electrical connections to the battery/motor/charge port. So replacing the circuit board would probably be a 10 minute job at a repair shop. But of course I dont have a replacement.I confirmed that my "broken" shaver is in fact completely functional - motor spins, battery charged properly. A full day of reverse engineering later and I was able to guess that the 3.3V rail just needed to be bootstrapped. If you power on the 3.3V rail externally with a power supply, it stays on and the shaver is back to working.I have seen devices like this before - they have a "shipping/storage mode" where the battery is almost completely disconnected to prevent discharge until an external power supply is connected. Except this shaver doesnt come back on when plugged in to the charger. It remains in the disconnected state until you put 3.3V directly to the firmware flashing pads of the MCU.So I was hoping someone could take a look at the circuit board and let me know if there is a secret way to turn it back on externally.I suspect I will run into this problem again and if there was an easier way than needing complete disassembly, that would be super helpful.In the attached pictures, the goal is to get the 3.3V rail (annotated orange) to turn on using only the buttons or Supply +/- pins. In the lower right of the front side of the board there is a 5-pin device, which I assume is an LDO or similar. I think we are trying to get the enable pin (annotated green) to turn on. There is a whole bunch of resistor divider, capacitor, diode stuff going on on that green line that I havent figured out.Or does anyone have a source for decoding those markings on the ICs? If I could figure out what those 5-pin and 6-pin device are that would be super helpful!PS. I found it hilarious that this shaver has a 48MHz ARM M0+ (CY8C4146) just to blink 6 LEDs and turn on a motor. Oh well.

author: InvncibilityCloak
author_rank: Newbie
timestamp: September 01, 2025, 05:53:19 am
content: Okay I actually just searched on this forum for "braun" and found a different thread about a Silk Epil 9. Looks like they are a very similar design.The poster there mentions the BC847BS which is the 6-pin device marked "1F T" that I was looking for. I'll go digging through the rest of that thread.https://www.eevblog.com/forum/repair/identifying-qfn16-3x3-mm-buck-dc-dc-li-ion-charger/msg5069041/#msg5069041

author: iMo
author_rank: Super Contributor
timestamp: September 01, 2025, 06:18:09 am
content: Quote from: InvncibilityCloak on September 01, 2025, 05:45:32 amHopefully the chips there are rad-hard, as I want to use the shaver while traveling to Mars..

author: 5U4GB
author_rank: Super Contributor
timestamp: September 01, 2025, 07:01:13 am
content: Quote from: InvncibilityCloak on September 01, 2025, 05:45:32 amBunnie Huanghas a great post somewhere about the simplicity of complexity, that it's quicker and cheaper to make it complex than to make it simple. I can't find it ATM so either my Google-foo sucks (quite likely) or it was in one of his books.

author: Mario87
author_rank: Frequent Contributor
timestamp: September 01, 2025, 12:45:32 pm
content: Your "ShaverFrontAnnotated.jpg" file shows the LDO enable signal starts off at 2.7V with 12V supply, by the time it reaches the LDO its probably less (passing through the 16.5k resistor and also being loaded by other circuits).My guess is if you change the 16.5k resistor to something lower you will have less of a voltage drop and it might be just enough to keep the LDO enable signal live. Not sure what that LDO device is, but check the voltage on the EN signal when it does not work and check the voltage on it when it does work, then adjust the 16.5k resistor accordingly so it keeps the EN signal to the LDO high even when the battery voltage drops.Should be a permanent fix...

author: Peabody
author_rank: Super Contributor
timestamp: September 01, 2025, 01:58:31 pm
content: I Googled 'Braun series 7 won't turn on', and see there's a travel lock that's released by holding the power button down for three seconds, or ten seconds produces a "power reset".

author: gamalot
author_rank: Super Contributor
timestamp: September 01, 2025, 03:49:01 pm
content: The one with "ACJN" on top is an MP2615B:https://www.monolithicpower.com/en/mp2615b.html

author: BILLPOD
author_rank: Frequent Contributor
timestamp: September 01, 2025, 07:09:19 pm
content: Good Morning InvncibilityCloak, I'm afraid I can't help with your problem, but I just wanted to tell you how much I love your photos of the circuit board, and how you were able to color code it. I hope someone herecan help you bring your shaver back to life.

author: InvncibilityCloak
author_rank: Newbie
timestamp: September 03, 2025, 05:18:41 am
content: Thanks for all the help everyone! With the 6-pin device identified I put together a schematic.A simulation agrees that the 2.7V test point should be around 2.7V, which is a good sign.Quote from: Peabody on September 01, 2025, 01:58:31 pmYeah, tried that first. When the travel lock is ON there is a red LED lock icon that flashes. Mine was completely blank to all inputs. 10 seconds didnt help.Quote from: Mario87 on September 01, 2025, 12:45:32 pmI thought I had tried just shorting across the 16.5k and that it did not work, but thinking about that now and looking at the schematic, that doesnt make sense. I might do some more poking to see if this works.Interestingly, the 5-pin chip is marked D33 and a google search turned up R1180N331C for a D33 marking. Except the C variant is not supposed to have an enable pin, but on this board the enable pin is wired up and very much working (disabling the output).Anyway, I think I will just cut the trace to the EN pin and bodge the enable pin to the IN pin to permanently enable it. I dont see any reason for it to disable this regulator if that causes the shaver to be a brick.