MacBook 12 A1534 no sound, FaceTime camera hot, WLAN poor
If you have three simultaneous problems with a MacBook 12" A1534, then you may have damaged the display cable during a repair. Not the one that comes directly out of the display (that can't be changed anyway), but the one that leads from the small display board to the motherboard. This is glued to the lower aluminum bottom case and you have to remove it carefully.
If you are not very careful and take a spudger or something and just pull the cable off, you might damage the outer black coating and with it the small copper wires inside. Depending on where you damage the cable, this will cause some functions to fail.
In our case, FaceTime always reported that the camera was overheated. The sound output also failed completely. The internal speakers were also no longer displayed in the system settings. The WLAN also deteriorated significantly. Apparently, the connection to an antenna via the small cable was also affected.
The cable shows the damage quite clearly. And no, a bit of tape does not help. :) But practically, the display cable is very cheap and available everywhere: just replace it and camera, speaker and WLAN will work again.
Buy display cable: Amazon Aliexpress