In Case Of Difficulty - Sennheiser HD400 Instructions For Use Manual

Problem
Clear communication but no
active noise compensation
136

In case of difficulty

If problems occur that are not listed in the below table, please contact your Sennheiser
agent.
Possible cause and what to do
The NoiseGard™ electronics are turned off.
Check to see if the ON/OFF switch is set to ON.
The XLR-3 plug has been pulled out of the power source.
Check to see if the XLR-3 plug is correctly connected to the power source.
If aircraft powered: The aircraft fuse is defective.
Check the aircraft fuse.
If battery powered (except HMEC 302, HMEC 305 and HMEC 306): The batteries are low.
Check to see if the green LED on the battery pack is lit. If the red LED is lit, replace
the batteries.