If you've replaced the LM4766 ICs and the humming sound returned, there could be a few possibilities to consider:
- Grounding Issues: Humming sounds in audio systems can often be caused by grounding issues. Ensure that all components are properly grounded and that there are no loose or disconnected grounding connections.
- Power Supply Problems: The rapid loud hum could be related to power supply issues. Make sure the power supply is stable and within the correct voltage range. Also, check for any issues with the power cables or connections.
- Filter Capacitors: Check the filter capacitors in the power supply section and around the LM4766 ICs. Faulty or aging capacitors can lead to noise issues in audio systems.
- Signal Interference: Electrical interference from other devices or cables can sometimes cause humming sounds. Make sure the audio cables are properly shielded and not running too close to power cables.
- Speaker Connections: Double-check all speaker connections, ensuring they are secure and properly connected. Loose or damaged speaker wires can lead to noise issues.
- Board-Level Problems: There could be other components on the circuit board that are causing the issue. Inspect the circuit board for any signs of damage, burn marks, or soldering issues.
- Magnetic Interference: Make sure there are no strong magnetic fields or sources of interference near the system that could be causing the humming sound.
- Professional Help: If you've exhausted your troubleshooting efforts and the issue persists, it might be best to seek the assistance of a professional audio technician who has experience with Bose systems. They can perform more advanced diagnostics and repairs.
Remember that working with electronics and audio equipment requires technical expertise and can involve risks, including electrical hazards. If you're not comfortable or experienced with electronic repairs, it's advisable to seek professional assistance to avoid potential damage to the equipment or harm to yourself.