First, confirm the DAU and the SIU in the aircraft, not all units belong to Radiant Power.

Issues with the Radiant Power supported DAU's and SIU's are redirected to Radiant Power in Sarasota, Florida (USA):

Radiant Power (DAU & SIU) Repairs
7135 16th St E #101, Sarasota, FL 34243
(941) 739-3200 
7:30 AM - 4:30 PM Monday - Thursday Closed on Fridays