The Sennheiser's FAQ has been done to assist you in the troubleshooting.

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TV Listening Systems
Wireless Headphones
Wireless Microphones

1. Why is it when I plug my MKH416T or MKH816T into phantom power it doesn't work?
   
2. The LED on my K6 & MKE300 only flashes momentarily. Is it broken?
   
3. Why is the audio distorted when I plug my K6 and MEXX capsule into the mic input of my Camcorder?
   
4. My wireless system is noisy
   
5. Why is my headset intermittent on one side?
   

1. Why is it when I plug my MKH416T or MKH816T into phantom power it doesn't work?
   The "T" at the end of the Sennheiser nomenclature (i.e MKH416T) indicates that the microphone requires 12 volt "T" or "A-B" power which, is totally different than 48 volt Phantom Power. One method for using your MKH "T" mic with any phantom power source would be to use our 12T-P48 adapter that plugs inline between the phantom power source and the mic. The 12T-P48 converts the 48 volt phantom power to 12 "T" power and retails for $55.
2. The LED on my K6 & MKE300 only flashes momentarily. Is it broken?
   No. The LED was designed only to flash momentarily to indicate that there still is life left in the battery. If the LED were to be on all the time it would drain the battery too quickly. The battery life is rated for 150 hours of continuous use for both the K6 and the MKE300.
3. Why is the audio distorted when I plug my K6 and MEXX capsule into the mic input of my Camcorder?
   The K6 power module produces a very hot output, almost line level in some situations. When the microphone is recording in a fairly loud SPL environment, the resulting audio signal from the K6 is too large for the camcorder's internal mic pre-amp. The solution for this is to use the K6-RD power module. This version of the K6 has a reduced output level that will accommodate more sensitive mic pre-amps on some camcorders as well as other electronic equipment. You can purchase the K6-RD as is or, you can have your K6 easily converted to a K6-RD. The conversion will be performed at no charge if, the K6 is within its warranty period. Otherwise, the charge is $17.50+shipping for the conversion.
4. My wireless system is noisy
   Never control mixer board levels with transmitters sensitivity settings. The audio level/volume knob on the back of the receiver should be used for board levels. The sensitivity level of transmitter is set by looking at the receivers audio display. The ideal audio level is 3/4's of the way up the display scale. If the display level peaks every now and then that's good. Not enough audio level will result in a high noise floor.
5. Why is my headset intermittent on one side?
   Did you try to re-secure the connection or disconnect and switch sides to determine whether it is the cable or headset?