if Alpine
The fault is caused whenever a speaker lead is grounded to the vehicle chassis or other ground, not because it isn't grounded. First make absolutely sure that none of the speaker wires are grounding out. The best way is from the from the head unit side with a multimeter. Set the meter to read the lowest resistance scale (ohms), ground the negative meter lead, and probe the positive lead to each speaker wire. If you find a low resistance, repair or replace the wire.
Inside the faceplace near the bottom left, there's a little recessed pushbutton. Remove the faceplace and with a straightened out paper clip, tip of a ballpoint pen, or similar object, press the button for about 1-2 seconds. Then go into the "audio settings" and set POWER IC to POW ON. If this fails to work, the unit is probably defective.
xxxxx, December 2010
