JBL Quantum100 one side not working (how to fix)

In this video we are taking a close look at some defective JBL Quantum 100 headphones, where the left side stopped playing. We can only hear the sound on the right ear cup.
In order to figure out the problem with our headset, we open up the left ear cup and examine the driver, the wiring and the small PCBs.
In this case it turned out that the speaker itself was still working. So was the wiring to the speaker and the soldering work on the PCB. (We are using a multimeter in continuity-mode to check for problems)
It turned out to be a faulty auxiliary cable, which we use to connect to our computer or smartphone. (This model of headphones does not have Bluetooth)
In order to repair this problem, we will have to get a new auxiliary cable and replace the old, defective one - but this will be part of a different video...