There are generally two areas that cause problems with Sennheiser Lavalier & Headset Microphones.
The cable is intermittent where it exits the connector (or power supply if it is a hard-wired mic) or the connector is damaged or ripped off of the cable.
Mic element (head) is bad or blown or the cable is intermittent (or frayed or pulled out) where it enters the mic head.
Connector end issues are by far the most common problem that we repair. We cut the cable back about 1 inch from the connector and re-install the connector. We provide this repair service with a quick turn-a-round. Problems at the Head End generally cannot be repaired. For either problem, please see the below link to our microsite for details.