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I visited a popular electronics forum to ask about it, and one staff member left this message.Hope this thing can help you if you suffer from the same issue.-----------------------------------------------------------------Probably the capacitors although there could be other reasons. They are the three brown cylinders on the left of the board. They all eventually fail but I'm surprised they died so soon on a relatively new unit. Normally you would expect 5+ years before hum becomes noticeable. They are not expensive to buy and easy to replace.I'm not sure where you are but my guess is you have 60Hz mains power at your wall sockets. That is the clue, the bridge rectifiers (the four gray things with silver bands at one end near where the yellow and green wires reach) convert the 60Hz AC into pulsed DC at a rate of 120Hz. The capacitors act as reservoirs to hold the pulses at a steadier level before feeding the voltage regulator circuit. If the capacitors become inefficient the reservoir holds less and the pulses start to show across them and then conduct to the rest of the circuit.
I visited a popular electronics forum to ask about it, and one staff member left this message.
Hope this thing can help you if you suffer from the same issue.
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Probably the capacitors although there could be other reasons. They are the three brown cylinders on the left of the board. They all eventually fail but I'm surprised they died so soon on a relatively new unit. Normally you would expect 5+ years before hum becomes noticeable. They are not expensive to buy and easy to replace.
I'm not sure where you are but my guess is you have 60Hz mains power at your wall sockets. That is the clue, the bridge rectifiers (the four gray things with silver bands at one end near where the yellow and green wires reach) convert the 60Hz AC into pulsed DC at a rate of 120Hz. The capacitors act as reservoirs to hold the pulses at a steadier level before feeding the voltage regulator circuit. If the capacitors become inefficient the reservoir holds less and the pulses start to show across them and then conduct to the rest of the circuit.
