Hi
Alwas sad when something wrong happens with our keyboards.
Long time since I had a KN2k, but it's a great keyboard.
Some steps to try out:
1. If you use a swell/volume pedal, unplug it.
2. Check that volume for each part are above zero when look in display.
3. Try only the headphones plugged in, and push and drag the jack in and out a bit to see if there is a bad connect.
If nothing happens, sound still dead, it's probably the final transistor for outgoing sound that is defect.
If so, next step will be to visit a serviceshop.
KN2000 is probably less money as second hand at eBay than a repair will cost?
Hopefully your problems is sorted out very soon.
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Cheers 🥂
GJ
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"Success is not counted by how high you have climbed
but by how many you brought with you." (Wil Rose)