Motors
Faulty motors cause rotation problems on turntables and tape decks. On record players, try turning the shaft manually. If you meet resistance or hear squeaking, lubricate the motor bearings. If the shaft still doesn't turn smoothly, replace the motor. On tape decks, listen for changes in sound speed or crinkling noises. Rule out the possibility that the cassette is faulty by playing it on a working deck or test your player with a different cassette. Dirty or cracked pinch rollers on tape players can also cause improper playback and fluttering noises, so inspect these before replacing the motor.
Stereo amplifiers
Amplifiers and receivers produce bigger sounds by boosting the electrical current. If there is no sound, the stereo amplifier may be faulty. Inspect the fuses for smoky markings, which indicate a blown fuse. Check wires for loose connections. Test the system with a different speaker to rule out speaker problems. If you find nothing else wrong, replace the amplifier.