[BackwardPawn]

I ended up taking my DT880s to a local electronics repair shop since I didn't want to have Brian work on broken headphones and the factory center isn't open yet.  The guy had good reviews and seemed competent (I left the first shop as he used a multimeter on two pieces of metal the didn't even complete a circuit).
 
Anyway, he said he'd put a new end on and have them back to me in a day.  Three days later I call him up and ask what the status is and says he's perplexed and has seen nothing like it before.  He's taken it appart and put it back together and it still has the same problem.   He said both drivers appear to work perfectly individually and depending on what he plugs it into, sometimes they work at the same volume, sometimes different volumes.  The TRS checked out and the cord checked out.
 
He doesn't want to change any components because he said everything works, but when the headphones are put back together, the left channel is just much lower than the right on some devices.  He said he was using them on a Samsung CD player as I called and they worked, but he's tried them on other sources and they don't.  He said if he can't figure it out tonight, he's going to call Beyer and ask if they've ever run into this problem before.
 
I paid him $20 to diagnose the problem and his assistant said he was working on them yesterday when I called, and he was working on them today when I called...so I guess I'm getting my money's worth, just wish I had headphones.  My inclination is still a bad TRS, but he said the TRS appeared to check out and he didn't want to change it until he was sure.

 

[NA Blur]

Seems like a grounding issue to me.  Sometimes the ground wires are quite small on headphones making them difficult to solder / reinstall.  You can have him measure the resistance between the ground cable and both drivers.  If they differ wildly then this is most likely your issue.\
 
The other thing I can think of is a possible impedance mismatch between the two sides.  Perhaps a resistor is missing from one of the sides?
 
The last thing is that it could be the TRS connector itself and its insertion depth.  Is the connector on the headphone now a replacement?  It may be that it fits nicely into the jack on some units and poorly into other jacks.  This is often found in cheap TRS connectors that have poor Tip / Ring/ Sleeve spacing.

 

[BackwardPawn]

Its the original TRS connector.  I was thinking that it may have gone bad and be hitting the wrong spot on different units.  I suggested this, but he said until he could confirm this, he didn't want to start ringing up a bill.  I'll call him back tomorrow and ask if he checked that the grounding is the same on both drivers.  Just curious, but how does an impedence mismatch suddenly pop up, plus I think he'd notice a missing resistor since he's disassembled them, but I'll mention that too.

 

[BackwardPawn]

The grounding on both sides is fine.  He can send a signal from a 1.5v battery down the line and get equal sound on both sides.  He says the TRS checks out and the headphones work perfectly with some units, but the left channel just doesn't work on other units.  My laymans take is still that the TRS is at fault, but he said he doesn't think the TRS is the issue and doesn't want to change it just to run into the same problem.  He's putting them back together and suggesting I give them to the factory shop once they're open again.  Any other ideas before I pick them up?
 
EDIT:  Everythings been closed back up and the technician assured me that no one can tell they've been checked out since he knows they're going straight in to the factory shop.  Please no more replies as I'd like this thread to disappear into the ether.  Thanks.

 

[NA Blur]

I am with you still on the connector.  Change it out for a high quality connector as soon as you can.