Dead left-side headphone cup

@paulwilliamsjnr could be an issue with the jack, the wire, the connection to the driver (speaker) or the speaker itself. To get to that is actually pretty simple. Use something like this video (turn the volume down. the music ¯\_(ツ)_/¯ ) Once you get to the wire on the speaker, check the wiring. Use a multimeter and one probe on the jack and the other one to the speaker to see if you have continuity on each cable. That is a bit tricky since we do not know which wire goes where. Post some pictures of the wiring once you are getting to the speaker as well as of the jack that plugs in. That way we should be able to figure it out and provide you with more directions.

Adding images to an existing question