Sennheiser SKM 9000 Instruction Manual page 94

Cleaning and maintaining the Digital 9000 system
Cleaning the contacts of the SK 9000 bodypack transmitter
Wipe the contacts with a dry cloth.
Cleaning the L 60 charger
Remove all accupacks from the charging compartments.
Before cleaning, disconnect the NT 3-1 mains unit from the mains.
Use a dry cloth for cleaning.
Use a brush or similar to remove dust from the charging compartments.
Clean the charging contacts from time to time using e.g. a cotton swab.
Digital 9000 | 93