Mazda Bose KU060 amplifier “machine gun sound”

Problem

A Bose car audio amplifier came in for repair, the customer reported that it made a loud machine gun type of sound from all the speakers. They had unplugged the speakers to make the noise stop but wanted the car audio to work again.

Diagnosis

We found that a dual output voltage regulator that supplied 3.3V and 1.25V had failed, the 1.25V output was actually supplying 2.5V and this had damaged a DSP IC which processes all audio signals.

Solution

We replaced the voltage regulator and checked the output voltages were correct, then replaced the DSP. The amplifier works normally again.

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