Common problem diagnosis and solution for power amplifier failure

No Power Supply:

First, check if the power cord is properly connected to the fuse. Ensure that the power cable is not damaged or broken. Also, verify that the fuse is functioning correctly and not blown. If the fuse is faulty, replace it. Next, inspect the rectifier bridge or electrolytic components in the power amplifier’s power supply section, such as diodes or bridge stacks. Check for any other potential issues in the power circuit, including the power amplifier tubes.

Signal Indicator Lights Up, but No Sound Output:

Start by checking if the speaker unit is working properly. If the speaker is fine, test the speaker cables for good contact at the terminals. Open the case and visually inspect the connections or listen for the output relay to engage. If the relay is not closing, check for oxidation or damage on the contacts. If the contacts are faulty, replace the relay.

Power Light Works, No Sound, but Relay Sounds:

Use a multimeter to check if the power supply to the amplifier is stable. If the power is normal, touch the signal input with your hand to see if you hear a loud current, which indicates the pre-amplifier stage is likely okay. Then check the signal line for poor connections or broken wires. If there is a problem, use the multimeter to locate and fix the fault.

No Sound from Amplifier Output:

Ensure the speaker is functioning correctly. Check for any burnt or loose terminals. If the terminal is blackened, clean it thoroughly and tighten the screws to ensure a solid connection.

Boot Protection Light Is On:

First, measure the resistance of the speaker coil using a multimeter. A normal reading should be above 30 Ω. If the resistance is low, there may be a short circuit. If the external wiring is fine, the issue is likely with the power amplifier itself. Check the power supply section for faults.

Sound Volume Varies:

1. Poor contact in the signal cable;

2. Faulty potentiometer contact;

3. Damaged signal coupling capacitor;

4. Poor contact in the feedback resistor.

No Sound After Checking the Motherboard:

1. The signal cable is disconnected or the coupling capacitor is open;

2. No power supply to the front-end section — check the power supply;

3. Faulty volume control potentiometer;

4. Faulty operational amplifier IC.

Distorted Sound from Pure Power Amplifier:

1. Soft breakdown in the power tube;

2. Insufficient or unstable voltage between positive and negative rails;

3. Faulty resistor values or component failures.

Level Indicator Not Working:

1. Check if the voltage is within the normal range;

2. Confirm if the signal is being sent properly;

3. Test the components for damage or failure.

Treble and Bass Controls Not Working:

1. Check if the potentiometer is functioning correctly;

2. Ensure the voltage is stable;

3. Verify that the RC components are in good condition;

4. Check for loose or broken connections in the wiring;

5. Look for cold solder joints or false soldering on the board.

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