The general consensus is to heat the solder joints to get them melted. If there was a bad joint, it should be fixed. If that doesn't fix it, try replacing some of the readily available chips that are on the board. If your skills aren't up to it, you will have to get a rebuilt unit.
I have written an article on soldering basics for another forum. Feel free to take a look for tips. http://elitecaraudio.com/tips/car_audio/soldering1.shtml