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HD Amplifier Troubleshooting Guide

“My amplifier doesn’t turn on”
Check the fuse(s), not just visually, but with a continuity meter. It is possible for a fuse to have poor internal connections that cannot be found by visual inspection. It is best to take the fuse out of the holder for testing. If no problem is found with the fuse, inspect the fuse-holder. Check the integrity of the connections made to each of the “+12VDC”, “Ground”, and “Remote” terminals. Ensure that no wire insulation is pinched by the terminal set screw and that each connection is tight. Check to make sure there is +12V at the “Remote” connection of the amplifier. In some cases, the turn-on lead from the source unit is insufficient to turn on multiple devices and the use of a relay is required. To test for this problem, jump the “+12VDC” wire to the “Remote” terminal to see if the amplifier turns on.

“I get a distorted / attenuated sound coming out of the speaker(s)”
Check the speaker wires for a possible short, either between the positive and negative leads or between a speaker lead and the vehicle’s chassis ground. If a short is present, you will experience distorted and/or attenuated output. The “Status” LED will turn amber (yellow) in this situation. It may be helpful to disconnect the speaker wires from the amplifier and use a different set of wires connected to a test speaker. Check the nominal load impedance to verify that the amplifier is driving a load equal to or greater than 1.5 ohms. Check the input signal and input signal cables to make sure signal is present at the “Amplifier Inputs” and the cables are not pinched or loose. It may be helpful to try a different set of cables and/or a different signal source to be sure.

“My amplifier’s output fluctuates when i tap on it or hit a bump”
Check the connections to the amplifier. Make sure that the insulation for all wires has been stripped back far enough to allow a good contact area inside the connector plugs. Check the input connectors to ensure that they all are making good contact with the input jacks on the amplifier.

“My amplifier shuts off once in a while, usually at higher volumes”
Check your voltage source and grounding point. The power supply of the HD750/1 will operate with charging system voltages down to 8.5V. Shutdown problems at higher volume levels can occur when the charging system voltage drops below 8.5V. These dips can be of very short duration making them extremely difficult to detect with a common DC voltmeter. To ensure proper voltage, inspect all wiring and termination points. It may also be necessary to upgrade the ground wire connecting the battery to the vehicle’s chassis and the power wire connecting the alternator to the battery. Many vehicles employ small (10 AWG - 6 AWG) wire to ground the battery to the vehicle’s chassis and to connect the alternator to the battery. To prevent voltage drops, these wires should be upgraded to 4 AWG when installing amplifier systems with main fuse ratings above 60A. Grounding problems are the leading cause of misdiagnosed amplifier “failures.”

“My amplifier turns on, but there is no output”
Check the input signal using an AC voltmeter to measure the voltage from the source unit while an appropriate test tone is played through the source unit (disconnect the input cables from the amplifier prior to this test). The frequency used should be in the range that is to be amplified by the amplifier (example: 50 Hz for a sub bass application or 1 kHz for a full range / high-pass application). A steady, sufficient voltage (between 200mV and 8.0-volts) should be present at the output of the signal cables. Check the output of the amplifier. Using the procedure explained in the previous check item (after plugging the input cables back into the amplifier) test for output at the speaker outputs of the amplifier. Unless you enjoy test tones at high levels, it is a good idea to remove the Speaker Connector Plugs from the amplifier while doing this. Turn the volume up approximately half way. 5V or more should be measured at the speaker outputs. This output level can vary greatly between amplifiers but it should not be in the millivolt range with the source unit at half volume. If you are reading sufficient voltage, check your speaker connections as explained below.Check to ensure that the speaker wires are making a good connection with the metal inside the Speaker Connector Plugs. The speaker wire connectors are designed to accept up to 12 AWG wire. Make sure to strip the wire to allow for a sufficient connection with the metal inside each terminal.

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