1. Reduce the power supply voltage of the audio part of the audio circuit pc board. For example, if the audio part voltage is positive and negative voltage 45V, use positive and negative 20V voltage to repair, which is safer.

　　2. When repairing the pc board circuit of the audio circuit, be sure to short-circuit the signal input end of the power amplifier to the ground.

　　3. The audio circuit pc board factory found that some speakers cannot remove the power tube for repair. After the power tube is removed, the midpoint voltage cannot be measured. The midpoint voltage is either positive or negative. And it is the positive or negative value of the power supply voltage.

　　4. If the audio circuit PC board is afraid of burning the power tube, you can do this: temporarily use the pair of tubes 2SA940 and 2SC2073 instead. Because the general home audio is not partial armour. The static current is not large and will not burn the tube, but the tube must be attached to the heat sink.

　　5. The component parameters on the bias circuit of the audio circuit pc board must be accurate. The bias transistor pin position and tube type must be connected correctly.

　　6. The "complementary pair" of the tubes used in the audio circuit pc board should basically have a magnification β of one to one.