If you do not find a fuse , you have blown a REVERSE POLARITY DIODE.
You ca find this Diode right beside or very close to the power supply inside the radio...Ive fixed a few radios for friends over the yrs...cost for 10 Diodes 50 cents...
total time to fix: 30 mins
Check that out...you might see the burnt diode tap the diodes around the supply ( TAP LIGHTLY ) If blown , they will fall apart ( Carbon ) .
Hope this can assist you