If you have a car amplifier that powers up just fine but produces no sound, there could be a variety of reasons for this issue. In this post, we will discuss one common diagnosis and fix for this problem.
One of the most common reasons for no sound or no output switching is that the output section of the class D amplifier isn’t operational. This means that the amplifier is not being fed with the correct voltages to work with. In this case, the pre-amplifier board needs plus and minus 12 volts to work properly. If these voltages are not present, the pre-amplifier circuit won’t work, and any voltages that are derived from the plus/minus 12 volts or plus/minus 15 volts won’t make their way to the output section drive circuit.
To diagnose this issue, start by powering up the amplifier and checking for power supply operation. If everything appears to be okay, check the output switching. If there is no output switching, probe pin number four of the preamplifier board for negative 12 volts. If that is present, probe pin number eight for positive 12 volts. If there is no positive 12 volts, the pre-amplifier circuit won’t work, and there won’t be any output switching.
To fix this issue, you’ll need to check where the voltage is generated. Start by checking the transformer and rectifier diodes that feed the voltage regulators. After the rectifier diodes, there should be a rectified version of the AC input. If that’s present, but there’s no voltage on the other side of the inductor, the issue is likely with the little green inductor that’s designed to smooth out or clean up the DC before it goes to the smoothing capacitor and voltage regulator.
By changing this tiny little piece, the amplifier section and pre-amplifier section should work just fine again. This quick diagnosis and fix can save you a lot of time and money compared to other issues that can cause no sound or no output switching in a car amplifier.