An internal electronic component on the audio circuitry has likely blown.
If you can still hear audio through headphones, then the speakers or part of their circuitry may have failed.
The keyboard will need to be opened and some diagnostic tests carried out to help locate the source of the fault.
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- they are the best repairers in your area.
You will need to loosen all of the screws around the edge of the keyboard, then remove the lower panel from the top panel.
Please attach a photo so I can confirm we are talking about the same model.