Chosen Solution

I realize that no audio in one ear is a common problem, but bear with me. I already tried to see if it’s the audio jack that is causing it and did all the common fixes, but no luck. Then I took apart the left side to try and see if it it was a wiring issue; yes and no. So the wire to the SP- on the PCB was not even connected, but upon soldering the wire to the pad, there was still no sound. I did a continuity test with my multimeter to see if a wire broke and I actually got a crackling noise coming out of the left ear, so I guess that’s not the issue. So now I’m stuck at this step and have no idea what to do (short of ripping apart all the wiring). Image of left ear PCB: https://i.imgur.com/l5NMG2x.jpg

I have same issue. I never will buy Sennheiser brand anything. This issue so common and you cannot fix it without damaging headphones

  1. Remove the right earpad. 2.Remove the small black stickers wich comouflate the screws.
  2. Undo the screws wich tighten the ear piece.
  3. Upon removing the ear piece, On the upper side of the ear piece you will see a line of several contacts wich are coresponding to contact surfaces on the ear piece.
  4. Clean the lot with oilless contact cleaner. Await the cleaner to dry for few minnuts.
  5. Essamble the ear piece as you desmantled them.
  6. Victory!!! It should work OK.

Looking at your solder work, it looks like you may have a short on the right hand side of the image there. The solder looks like it may be bridging two of the contacts.

I have the same problem but the audio works again when the headband is fully compressed, so I guess the issue is in the headband, not on the left speaker itself. Did you try disassembling the headband to see how the sound travels from the right driver (which seems to be the one with all the master controls and probably the receiver for Bluetooth as well). I haven’t tried to open it myself and was hoping someone knew how to do it without breaking them.