I’m going to look at some Bluetooth audio receivers and more particular amplifiers and showcase how to repair them in case they fail. If your Bluetooth audio receiver doesn’t work anymore than the first thing to check is that it has adequate power. To do this, I would recommend using a voltmeter. Simply plug in the power supply which is shipped with the receiver and measure the voltage that is supplied by the power supply. The number that is shown by the voltmeter should match the number which is printed on the label which is attached onto the power supply. If the voltage differs significantly from the nominal voltage then it is time to swap the power supply. You can purchase another power supply either from the original manufacturer or from another manufacturer.
If you decide to purchase from another manufacturer that you have to make sure that the voltage as well as the current matches the rating of the original power supply. Also, make sure that the plaque of the power supply is the same diameter. Finally, ensure that the polarity of the DC plaque is the same. If you do pluck a power supply into your receiver that has the right polarity then the worst case scenario is that it can irreparably destroy your receiver.
Also, most manufacturers will not warrant their products when used with the power supply that is not purchase from the original manufacturer. Once you’ve checked that power is adequate, it is time to see if anything is wrong with the connectivity. Use a device that you haven’t used before and search for Bluetooth devices. The receiver should be displayed. If it doesn’t then power cycle the receiver and try the same process again. If the receiver is not visible then it is time to send it in for repair. Also, once the receiver has paired up but you still get no audio it is time to verify that the connecting cables between the receiver and you amplifier are okay. I would recommend to simply switch the connecting cable with a new one. If you still get no sound then again it is time to send the unit in for repair by a qualified service facility.