If you enjoy high quality audio playback in your car, you may have decided to invest in a premium quality car stereo system with a separate amplifier. The difference between a high quality stereo system with amp and a regular car radio is power. The typical car stereo has a small amp that powers the speakers. A separate, dedicated car amplifier is capable of driving the speakers a lot harder. This generates more volume. If your CD player or radio appears to be working, but the speakers aren't generating any sound then it's likely that there is a problem with your car amplifier.
Troubleshoot the car audio system to confirm a problem with the amplifier. Turn the ignition key so that battery is engaged. Check the volume settings on the stereo to make sure it is delivering sufficient signal to the amplifier.
Inspect the car amp. If the power light indicator comes on but the amplifier fails to generate power to the speakers, the problem is likely to be located in the output stage of the amplifier. If the power light indicator fails to come on the problem is likely to be located in the power section of the amplifier.
Unscrew and remove the amp but leave it wired in. Most separate amps are located in the boot of the car. If your amp is fried it likely to be because of a blown fuse, shorted transistor or damaged transformer. However it's smart to check for obvious causes such as loose wires and physical damage first.
Open up the amplifier chassis and use a flash light to inspect the circuit board. Replace any damaged wires and loose parts. If you spot any loose wiring, disconnect it and then make a new connection with your soldering iron. The circuit board inside the chassis will have an array of surface-mounted parts, such as transistors and resistors. Gently push each one to make sure the are securely attached to the board. Unscrew the circuit board and flip it upside down. Inspect the solder joints on the base. Melt any bad solder joints and make new ones.
Measure the transformers. Your power transformer takes the current from your car battery and uses it to add power to the audio signal from the stereo. Your output transformer adds voltage to that signal and sends it to the speakers. Damage to either can fry your amp. Turn the car ignition off and attach your meter leads to the primary winding on the power transformer. If you get anything lower than the idle current of the car battery, replace the power transformer. If your power transformer has a secondary winding, test that too. Turn off the ignition, disconnect the meter leads and reattach them.
Turn on the ignition and check the reading. Then perform the same test on the output transformer. If the output transformer gives a lower reading than the power rating listed in the amp's user manual, use the multimeter to check for shorted fuses. Check each transistor, starting with the one nearest to the output transformer. Replace any that give a low reading.
Test out your multimeter on a working stereo to calibrate it.
Exercise extreme caution when testing any internal part of your amplifier. There are potentially fatal currents running through your amp, whether it is fried or not.