I’ve just sent my Lightspeed in today for exact the same problem. I normally let the authorised repair centre carry out the repair. After market support has been great so far.
p.s. Sorry, I didn’t have a broken cable, just a broken outer shell, plus insulation.
It probably got caught somewhere between a door or something. Or a minor cut/scratch that weakened the cable assy.
I have the headset cable of my Sennheiser S1 Digital damaged with multiple cuts, exactly as shown on @Vladimir s photo.
The cable still works and I fixed it by wrapping tape around it.
It’s unclear to me where these cuts come from. The DA40 has fixed seats so it can’t be that the cable got stuck between the seat sliders. It’s my personal headset and I always take it home, so it’s not used that much. The standard David Clark headsets which are in the aircraft don’t have the cables damaged.
So the most valid explanation would be that the cable get damaged by the zipper of the headset case…
It’s not that old but I don’t have any purchase documents any more and also warranty probably does not cover cutting the cable.
The HME100SE had a 10 year warranty if I remember correctly – how old is the headset?
NB for this kind of soldering job, a marvellous tool can be created by glueing two clothespins to any suitable support.
I rather think some modicum of connectivity remains because a very few strands of copper aren’t broken yet – but don’t count on it to last.
If soldering is not your kind of speciality~ you should have someone near at hand. At least resort do feel free to fly over to BE and I’ll merrily do the job for you – even issue a certificate of guarantee (no EASA rubber stamp, though) for your home flight, at least – though I might take longer than Peter’s 10-20 minutes. And sorry to infringe upon Jesse’s market – if you want the job done to professional standard, fly just slightly beyond my little country.
~ us sysadmins always have reserves about application developers’ practical abilities ;)
Vladimir, just get the soldering iron out and be done with it. I thought you were a pretty switched on and practical guy from all your previous posts, now I’m not so sure :)
You underestimate software developers, Peter 
I can damage any cable completely by trying to fix it
I thought about it but the broken wire is very thin, so thin that I don’t even see the wire itself, it’s almost like it’s just the isolation. And my experience is that it goes very wrong when I try to solder so fine wires.
Any idea why the headset is still working fine? Could it be that this exact wire is not used?
This is trivial to repair.
The wires are coloured so trivial to join back up.
Cut out the damaged 2cm or so and join it back up, with heatshrink on the individual wires, and heatshrink overall. 10-20 minutes.
If you can disconnect the cable assembly I will do it for you 
But then so can anybody who can spell s o l d e r i n g
No trade-in programs (that I know of) in Switzerland and sending it in and back to another country + the import tax costs more than the discount you get ;(
