No sound from headphone

Worse case scenario is that your left speaker is gone but usually what happens is a break in the cable someplace.Are you using the 1/8" plug or are you using them with the 1/4" adapter. The 1/4" adapter might be worn out but is easily purchased and replaced.The cabling from the plug runs into the left can and from there splits into left and right speakers. There will be a wire that follows the head band under the cushion from left to right. With these headphones there is a swivel above the can and the problem might be in there. Half the problem is getting at the wiring to test it. Usually the plate that the speakers are mounted on is screwed to the back cup and the screws can be reached by removing the earpad. You will need a volt ohm meter to test the wiring. You can also test the speakers with it. Unfortunately most plugs on headphones are molded onto the cable so you will have to start by testing from the plug to the left can. Inside the left can will be a junction point where the main cable feeds the right speaker. Test up to there for right and left and if the connections are good then test the speaker. Hope this helps.