How to Repair Common Power Amplifier Faults
1. The Entire Unit is Not Working
Symptoms:
The amplifier shows no display after power-on, all function buttons are unresponsive, and no sound is produced, as if the device is not receiving power.
Maintenance Method:
Start by checking the power supply circuit. Connect the power and measure the DC resistance at both ends of the power plug using a multimeter. A normal resistance reading should be several hundred ohms. If the reading is much higher or the power transformer overheats, it indicates a partial short circuit in the transformer’s primary circuit. If the reading is infinite, inspect for an open circuit in the transformer’s primary winding, a blown fuse, or a disconnection between the plug and power cord.
2. No Sound Output
Symptoms:
Although the function buttons work and the status is displayed, there is no signal output.
Maintenance Method:
For amplifiers with a protection circuit, check whether the protection relay activates when powered on. If it doesn’t, measure the midpoint voltage in the power amplifier circuit, check if the overcurrent detection voltage is normal, and look for any output voltage offsets. If the midpoint voltage is offset or the detection voltage is abnormal, it suggests a fault in the power amplifier circuit. Next, verify if the positive and negative power supplies are functioning properly. If they are asymmetrical, disconnect the load circuits to determine if the issue lies in the power amplifier circuit or the power supply itself. If the power supply is fine, check for damaged amplifier tubes in the circuit.
3. Low Sound Output
Symptoms:
The volume is significantly reduced, as the amplifier’s gain decreases or output power is reduced during audio transmission.
Maintenance Method:
First, check if the signal source and speakers are functioning correctly, using replacement components if necessary. Then, examine the transfer switches and control potentiometers to see if adjusting the volume improves the issue. If everything seems normal, test if the fault is in the pre-amplifier or power amplifier stage. For a specific channel with low sound, switch the pre-stage signal to another post-stage circuit. If the speaker volume remains unchanged, the problem lies in the post-stage circuit.
4. Loud Noise
Symptoms:
The amplifier produces various noises, including hum, crackling, induction noise, and white noise.
Maintenance Method:
First, identify whether the noise originates from the pre-stage or power amplifier stage. Disconnect the signal plugs between the stages—if the noise decreases significantly, the issue is in the pre-stage circuit; otherwise, it is in the power amplifier circuit.
How to Maintain a Power Amplifier
- Placement:
Place the amplifier in a dry, well-ventilated area, avoiding exposure to moisture, high temperatures, or chemicals. Avoid placing it in corrosive environments. - Positioning:
Ensure the amplifier is placed on a secure and stable surface to prevent it from falling or being damaged, which could lead to accidents like fire or electric shock. - Avoid Electromagnetic Interference:
Keep the amplifier away from strong electromagnetic interference, such as aging fluorescent lamp ballasts, which can disrupt the amplifier’s CPU and cause malfunctions. - Reset Function Keys:
After using the amplifier, reset all function buttons. Leaving them engaged for extended periods can wear out the button springs and lead to malfunctions. - Volume Control During Power On/Off:
Always set the volume potentiometer to the lowest level before turning the amplifier on or off. This minimizes the risk of damaging the speakers due to misoperation. - Regular Use in Humid Seasons:
In humid and hot seasons, turn on the amplifier for at least half an hour each day to prevent moisture from affecting internal components like coils and transformers. - Cleaning:
Periodically wipe the amplifier with a clean, damp cotton cloth. When not in use, cover the unit to protect it from dust. - Operating Temperature:
The ideal working temperature for audio equipment is between 18°C and 45°C. Operating below this range can reduce sensitivity, while higher temperatures can cause component damage or premature aging. In hot weather, ensure proper ventilation and cooling.