I have remote RC 505 -- I'm new user - unit went into protect mode and it doesn't respond to remote. With unit face closed I don't know where to find model designation to see correct model. It has CD and Sirius capabilities.

If the unit is in protect mode then there may be the possibility that the speaker wires may have a short circuit in them or that the amplifier section may be damaged....you can remove the radio from it's sleeve and check the wiring behind the unit...this also would have to be done to see the model number and serial number...it should be on either the top or bottom of the unit...the speaker wires for this unit are the white, gray, green, and violet...each with another of the same color but has a black stripe in it...the black stripe is the negative side of the speaker wire....you can disconnect these wires, then turn on the unit to see if it comes out of protect mode...if it does, then there is either a bad wire somewhere in the car or a bad speaker...if the unit stays in the protect mode, then you will have to take the unit in for repair, as this indicates a circuit failure