How to Repair a Bose 4.0 Amplifier on a Cadillac

By Simon Foden

New Bose amps have digital signal processing, managed by the circuit board.
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Certain Cadillacs come fitted with Bose audio systems. For example, older versions of the Cadillac STS has a Bose 4.0 audio system, newer versions have the Bose 5.1 system. The Cadillac SRX also comes fitted with an integrated Bose audio system. The numeric denotation in the name of the audio system refers to the type of surround-sound used in the system. The amplifiers are fundamentally the same in terms of design. If you are experiencing diminished audio playback, your amplifier might need repairs.

Troubleshoot the audio system. To ensure that the amplifier is the cause of the problem, turn on the ignition and send an audio signal to the amplifier, either by playing a CD or switching on the radio. If there is no sound, but the stereo control panel is on, the amplifier is the likely cause. If there is some sound, but it is crackly or only coming from one direction, the speakers might be the cause.

Locate the amplifier. The Bose amplifier in a Cadillac is typically located in the left panel inside the trunk. Pull back the carpet to expose the plastic trim panel. Use a cross-head screwdriver to remove the trim panel.

Turn off the ignition. Disconnect the amplifier. The Bose 4.0 amplifier in the Cadillac STS is 425-watts. This is a potentially lethal amount of power, so exercise caution. Disconnect the power wire (red), remote wire (yellow) and the ground wire (black). Tape the remote wire and ground wire to the inside of the trunk to keep them out of the way. Don't tape the power wire because you need to reconnect it for testing.

Remove the amplifier. Unscrew the screws fixing the bracket tab on the amplifier to the bracket. Lift the amplifier out of the bracket.

Open the chassis. Unscrew the lid and place it to one side. Stick the screws on a piece of electrical tape to stop them rolling away.

Place the volt meter probe directly onto the board-mounted component.
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Plug in the power wire. Turn on the ignition half way so that the battery is engaged and the amplifier is powered. Set your volt meter to "Ohms." Place your volt meter on the first resistor in the signal chain and note the reading. Repeat this for all resistors on the circuit. If any resistor gives a zero reading, remove and replace it. Only a blown resistor gives a zero reading. Consult the User's Manual to identify the correct power rating for the amplifier. If any of the transistors gives a reading outside the 5 percent variance threshold, replace it.

Turn off the engine. Use a soldering iron to melt any loose wiring wiring between the circuit board and the IEC power supply socket. Brush away the solder residue and reconnect the wire.