Car Audio Amplifier Troubleshooting

A question often asked is how to troubleshoot a car audio amplifier that is not working. This is different than an amplifier that is in protection mode but it is related. If you believe you have everything connected properly but the amp doesn't turn on, or if there is no output, these steps should help you track down the problem. A car audio amplifier needs several things in order to work and we'll check for each of these in the steps below.

1. Is the amplifier mounted to a non-conductive surface? If the case of the amplifier is touching the metal of the vehicle, either directly through the case or through the mounting screws touching metal, there will likely be a problem. Usually this will put the amplifier in protection mode though sometimes it may not turn on at all. First, ensure that the amplifier is not touching any conductive surface of the vehicle.

2. Is the amplifier getting the correct power and ground? The amplifier needs a positive power input and a negative power output. The power to the amplifier must be able to get in and get out in order for anything to happen. If the wiring is not correct, if it is too small for the amplifier, if a connection is loose or if a fuse is blown you'll get no output.

If the amplifier has a built in fuse check that it is in good condition and not blown. Do not rely on a visual inspection but instead remove the fuse (with the amplifier off) and test its continuity with a multi-meter. It should read close to zero ohms. Use a voltmeter to check the voltage between the positive and negative terminals of the amplifier. It should read about 12 volts with the engine off and upwards of 14 volts with the engine running. If it is not receiving power check the connections for both the power wire and the ground wire at any point they could come loose (grounding bolt, distribution/fuse block, outboard fuse holder, battery connection, etc.).

3. Is the amplifier receiving a turn on signal? Amplifiers need to receive a positive power signal on the remote turn on lead in order to turn the amp on. This is basically the on/off switch of the amp. You wouldn't want to use the main power wire as the switch so the amp has an internal relay that turns the amp on or off. This signal is provided by the head unit of an aftermarket (non-factory) radio/CD player through the dedicated turn on or "remote" lead. This lead is usually blue or blue with a white stripe but could be different so check your manual. Some head units will have two blue leads. One will be to turn on amplifiers and other processors (active crossovers, equalizers, etc.) while the second lead will be dedicated to the power antenna. The power antenna lead will only be active, or have power, when the radio is on. It will not have power when another source such as CD is selected. If your amplifier only works with the radio you may have the power antenna only lead connected to the amplifier instead of the remote lead.

If you have a factory radio you will probably not have a dedicated remote lead. In this case you can either use a switched power wire or purchase a unit that senses a signal on the factory speaker wires and uses that to trigger a remote turn on signal for the amplifier.

Test this connection by turning on your head unit to a source other than radio. Use a voltmeter and check the voltage between the remote terminal of the amplifier and ground. It should be around 12 volts. If it isn't change the head unit to the radio and see if it has voltage then. If it does you probably have the power antenna only lead connected instead of the remote turn on lead. If you do not have voltage in either case then your remote turn on lead is not working. Check the connections and if they are secure check the voltage directly at the head unit (you'll have to pull it out of the dash enough to access this lead. There should be a small fuse in that lead that may have burned out. Or if there is no fuse the circuit itself may have burned out. If that is the case you would need to have the head unit repaired or use a different solution for your remote signal. Use a small jumper wire between the positive amplifier terminal and the remote turn on terminal in order to continue the next tests. This is only temporary and the jumper wire needs to be removed after the tests or the amplifier will remain on at all times.

4. Is the amplifier receiving a music input signal? In order to get music out you have to have music in. This is either provided through the low level RCA jacks or through the high level speaker inputs (not all amplifiers have these, not to be confused with speaker outputs). Almost all aftermarket head units have at least one pair of RCA outputs. Some may have up to three pairs of outputs (front, rear, subwoofer). Factory head units will only have speaker outputs which can be connected to high level inputs or converted to low level (RCA) outputs by an adapter. Some newer head units and many premium (i.e. Bose, Infinity, etc.) have speaker level outputs that require special and more expensive adapters. If you have one of these systems it's best to seek out a qualified installer or contact one of the many adapter manufacturers (PIE, PAC, etc.) so they can help you choose the correct hardware.

If these connections (either low or high) are present and connected properly, check the gain of the amplifier. This is what matches the output signal of the head unit to the input section of the amplifier. With the head unit on and the volume at about half adjust the gain control on the amplifier and see if any sound is produced. If it is you can continue to adjust the gain on the amplifier. If not you need to find out if the amplifier is the problem or if it is the signal.

The fastest way to see if it is the amplifier is to connect a known good signal to the amplifier's input. I like to use a portable music player (CD or MP3) with a 3.5mm to RCA adapter cable on the headphone or line output jack. Using this known good source on the amplifier tells me if it is lack of signal that is causing the problem. If the portable player does cause the system to begin working then you know it is a problem with the input signal. This could be a poor connection or another unit upstream such as a crossover that is stopping the signal between the head unit and the amplifier. If any component between the head unit is stopping the signal then it needs to be checked out as well. The easiest way to isolate the unit for these tests is to simply bypass it and run a signal directly from the head unit to the amplifier. If the known good input does not help then it could be the input signal or the output. Leave the known good source connected for the next test.

5. Is the amplifier outputting a signal? Test the output of the amplifier by first disconnecting the speaker wiring from the amplifier. Then use a known good test speaker and connect it to one channel of the amplifier at a time. If the test speaker works on all channels then you know it is something after the amplifier. This could be non-functioning speakers, problems with the speaker wiring or simply a bad connection. If the amplifier turns on but there is no output to the test speaker than you know it isn't a problem after the amplifier. And since you've checked the power and input signals to the amplifier this only leaves the amplifier itself as the problem.

If none of these tests show the cause of the problem and you believe your amplifier is defective contact the manufacturer first, especially if the amplifier is still under warranty. Many have flat repair rates that are very affordable and cover parts and labor. However local repair shops may be cheaper if it is just a small repair. Compare the manufacturer's repair rate to that of a local shop. If you don't know the reputation of the local shop it may be better to send it to the manufacturer who will have working knowledge of the amp and parts readily available.


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