The first thing that I would try is removing power, either by the fused power lines (both of them) going to it or removing the fuses from the fuse block, if the power is routed thru a fuse block panel. Then try re- powering the unit to see if it goes back to normal. I said both power lines because one is normally a red wire and the second line is an 'always powered' line that keeps the radio memory for preset stations, clock, etc.
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