Right cup stopped working and left cutting out on 2-3 second intervals

Bose QC 35 II – Right Cup No Audio/Left Cup Intermittent Audio (Help Needed)

I’m having an issue with my Bose QC 35 II headphones, which started after a 4-foot drop onto a hard surface. The headphones landed on the left ear cup, leaving a visible scuff mark. Initially, the headphones seemed to work fine after the drop, but after 1 or 2 uses, they began to crackle and screech. Eventually, the right ear cup lost all audio, and the left ear cup’s audio became intermittent. The right ear cup is now completely silent, while the left ear cup cuts in and out every 2-3 seconds. I also hear a faint click or pop from the left driver each time the audio engages.

The power remains on without issue. Upon further inspection, I found that the left ear cup’s ANC microphone (wrapped in black rubber) has a lot of play. This microphone connects to the main PCB board on the left side. Occasionally, pressing the microphone into a certain position temporarily fixes the problem, restoring audio to both cups without interruptions. This led me to believe that the issue could be related to the microphone’s wiring, a faulty microphone, or a potential issue with the PCB.

I took the headphones to an electrical repair shop, where they tested the microphone’s two wire connections. The wires checked out, but the microphone itself was found to be intermittently working. Now, I’m trying to source the exact microphone (or an equivalent) to replace it and resolve the issue.

I’ve included pictures of the microphone (part number Q8207) and the left PCB board (part number 795794-0010) where the microphone is typically soldered. I’ve found used complete boards for around $100 (including shipping), but I’d prefer to just replace the microphone if possible.

My best guess is that the microphone is a cylindrical electret condenser type, around 5mm x 2mm, with an estimated resistance of 650-850 Ohms, according to the repair shop.

Does anyone know the manufacturer of this microphone or where I can source an equivalent? Bose is not offering to repair or sell a new PCB, and although there are refurbishers, the cost—including shipping—would be around $200 CAD.

Note: I’ve tried several solutions, including using electrical tape to prevent any wires from grounding against the case, rolling and pressing paper into the driver, and even bending the silver cable upwards to avoid contact or interference, as suggested in various online forums. I’m also aware of the power switch issue, but the headphones are powering on and off as they should. Given all of this, I’m confident that the problem is related to the ANC microphone. Also, what leads me to believe this is when I use the Bose app and change ANC from high to low the popping/clicking in left cup decreases significantly and when I switch to off, you can just barely hear the continuous clicking.

Thanks in advance for any help!

UPDATE:

I purchased a used working donor parts QC 35 (series 1) headphones [Cost $50 CAD]. Had the ANC microphone (Q8207) tested at the same shop as before with the known good part vs. the one thought to be faulty. It was inconclusive.

So we moved ahead with the full left main PCB board replacement, but the same issue still persists.

I think I've identified the problem. It seems that when the headphones were dropped onto a hard surface, the metal ear cup hit the action button ribbon (Part # Left Earcup Button Flex 789449-0010-01), potentially cutting or shorting it internally.

Previously, when I moved the microphone around on the left main PCB board and it started working, I believe I just got lucky and accidentally created a brief 20-30 second connection within the action button ribbon of the left ear cup.

My main concern now, is that before I took the headphones in for the left PCB main board replacement, I took a picture of the action button ribbon, and it appeared to be in significantly better condition than when I picked it up from the repair shop. This suggests that the ribbon may have been damaged, by the technician, during the repair, and it still may not be the original cause of the issue.

Here’s the picture before the repair:

And here's how it looked after the replacement of the left main PCB board that cost $70 CAD for service:

I tried moving the action button ribbon around to see if I could temporarily restore the connection, but it didn’t work. The ribbon was too badly damaged, and the bend it needs to make, to go from the board to the physical button, combined with the metal ear cup covers proximity likely caused a short or further damage.

The action PCB ribbon eventually broke. Afterward, I removed the action button and the entire PCB ribbon for the action button, as shown here:

The next step is to replace the action PCB ribbon, even though the repair costs are already high and it might not be cost-effective at this point. If I decide to purchase and install the part, I'll update my findings.

However, I’d recommend that others experiencing similar issues check this ribbon as it could also be the source of their problem.

Ribbons are available online, but only used. Good luck!

UPDATE 2:

Ordered a used action PCB Ribbon (Part # Left Earcup Button Flex 789449-0010-01) (cost ~$55 CAD) [$175 CAD deep on the repair so far, not making a lot of sense], should have it in a few days. I'll try to remember to update everyone if this is successful or not. More interested in actually fixing it than whether the repair is worth the cost, at this point. :)

UPDATE 3:

Tested the headphones passively with the wired audio jack with the power switched off and headphones work great, clear in both ears with no interruptions. Once I turn the headphone power switch on, the original issue (right ear no audio, left intermittent every 2 seconds) comes back.

Very confident this is being caused by either the damaged action button PCB ribbon as it activates Active Noise Cancelling. Or this is a short or damage to do with bluetooth components or board where it is located.

To try do bypass the Action button from activating ANC I changed the action button setting in the Bose app to Alexa assistant versus activate ANC, however, this did not make a difference in the devices behaviour.

I also read that when the 2.5mm audio jack gets plugged in the bluetooth is immediately deactivated. So if when plugged in with the audio jack and the power switch is on, the problem persists, we know this is not bluetooth related, as the bluetooth is off, and it is likely entirely Active Noise Cancelling related.

UPDATE 4:

Replaced the PCB ribbon action button for the ANC on the left ear cup. This did not resolve the issue.

Moved attention to Right Ear cup main board and found when pressing down in a certain spot on the board where the gold ribbon cable attaches to the right main PCB board I could get the product to work properly again. We tested the wires on the right board ANC microphone to see if the were shorting or not making a proper contact, but that was not the issue. Replaced the right ear cup main board and the problem has now been solved.

We believe there was either a short in one of the layers of the board on the ANC circuit or the microprocessor for ANC on the board may have had a bad contact.

Anyways, the solution is to replace the right main PCB board.

Hopefully this helps someone else, if they have the same issue occur.

Note: the donor left and right main boards were swapped into the Bose QC 35 II from a Bose QC 35 I. But it still worked.