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YDP-121 Yamaha Digital Piano - very low sound volume problem


May 20, 2020
May 20, 2020
I have a 10 years old digital piano model YDP-121. It was working well until last month the sound come out very low even it increased the volume to the highest. I've tried some testing and found that
1) if i play the demo song from the Piano, the sound will gradually louder but still not as loud as it used to be (I think it is loud about 50% of the original max volume)
2) even it plug in the head phone, the sound also not loud

From these symptom, i think there is something wrong with the amplifier circuit. I have visually check the main circuit board and power supply board, i cannot see any burnt or broken capacitor.
I just have little knowledge about the circuit, but can check the capacitor, resistor, or transistor.

I've attached the Diagram for this Piano model.
Please kindly help guiding me how to further check to solve this problem.
Please help point out which Capacitor in the Diagram that most probably effect to this problem, then i'll try to check it.


  • YDP-121 - Electrical Diagram.pdf
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