Microphone on Flightcom 4DLX (Blackhawk)

[Okavango]

I've got a pair of these for passengers which I picked up cheaply on Ebay. When I first tried them the mic wasn't working but once I found the switch on the lead (labelled M - S which I presumed were mono/stereo?) playing around with this seemed to get them fully functional. However, recently a passenger tried them and now I can't get the mic to function at all. Has anyone else had trouble with these and is it just a dodgy connection in the switch mechanism which turns the mic on/off or is it just that mics are flakey on cheaper sets?

[B2N2]

I picked up cheaply on Ebay

Mike should work fine, it's a wiring problem somewhere, maybe a broken wire from people always wrapping the cord around the headset too tight.