The 7.5 amp fuse is for the radio but also for the clock and instrument panel The 20 amp fuse is also for radio, clock and hazard flasher relay. The 7.5 amp fuse is for the radio memory and the 20 amp fuse is power to the radio. The 20 amp fuse is a switched circuit - power when the ignition switch is on. The 7.5 amp fuse should have power at all times.
Make sure the clock is working if so then the circuit should be good.
If you have no power at the 7.5 amp fuse check the 30 amp fuse at the starter solenoid. Also check to ensure there is power to fuse 3 in the fuse block. Fuse 3 is powered from the same circuit as the 20 amp fuse.
Good luck