What are fuses used for?

All electronic devices/circuits require fuses at the inputs to the power supplies. The exception being battery (DC) powered devices where maximum current draw is limited by the battery size.

Contrary to popular misconception by the ill-informed fuses (like all wire) have NO effect upon sound quality. To think otherwise is to believe in magic!

They are used to prevent damage to electric circuits from excess current. A fuse is a fine piece of wire with a selected melting point placed in series with one leg of the incoming AC voltage/current. If an electronic device draws too much current the fuse wire will melt and open. Preventing any AC voltage/current from entering the device. Thereby saving the device/circuit from further damage.

Look on the back panel. Near the AC cord/outlet you will see a round (usually) screw-type cap. Below it will be a designation indicating the size of the fuse required. Unscrew the cap and pull it out. The fuse is held at one end by the cap. It is a press fit. Pull on the fuse to remove it. Hold the fuse up to a light and observe the very thin wire within. If it is intact the fuse is good. If the wire is broken the fuse needs replacement. Replace only with a fuse of the same rating on the back panel.

Some fuse holders are square and require a push-in for release. Others are round and require a push-in with a twist before they can be pulled out.