[SOLVED] Odd issue with DT990 PROs

[ydoumus]

I know nothing about headsets, so this may not be odd at all. However...

My trusty 10 y.o. Beyerdynamics DT 990 PROs have finally started giving up. The left earbud cuts off, progressively losing volume output in a few stages over a second or so till it goes silent.
Out of frustration I lightly slapped the left earbud in a stereotypical russian fashion and, to my surprise, earbud started working again.

So I opened up the earbud and saw no visible issues; solder points were solid, no burnt areas or broken cables inside.

Does anyone know what could be causing this?

 

[hang-the-9]

Could still be a loose cable even if they look ok to your eye, re-do cables on the left side if you have the knowledge with wiring and soldering to do so. As an FYI, "earbud" is only a term used for in ear headphones, on a over the ear it's a "cup".