First, determine the fault range. Turn the volume down to the minimum. If the noise disappears, the fault is before the volume control. Otherwise, after the volume control.

After determining the range, manually test whether there are components overheating in the fault area. Overheated parts, replacement. If there is no abnormality, only two channels correspond to the measured voltage of the relevant part to determine which component is defective.

It is certain that some parts are defective.