My CTK-671 Casio keyboard with power on, has no keyboard sound

"Casio CTK-501 Digital Keyboard Troubleshooting - iFixit" https://www.ifixit.com/Wiki/Casio_CTK-501_Digital_Keyboard_Troubleshooting

Question moved to Casio Keyboards.

Take it in for service. Sounds like it needs a new switch or control board.

https://www.google.com/search?q=Casio+CTK+4400

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When wiring around circuit board cracks, one must use adequate sized wires and keep the leads short. Also you MAY have a microscopic crack in yet another conductor that flexes when you play the keyboard and freezes it. Use a high intensity LED light from the topside to "candle" the board and look for cracks. Look for cracking of the board material that may have tiny cracks in the circuit traces.

There probably is NOT a fuse and usual cause is problem with the adapter or the power connectors. Broken solder of the connector in the keyboard is common. Broken cords on the adapter is common as well.

First verify with a voltmeter that the adapter IS producing the voltage it is supposed to.

The cords and internals of these often fail.

Anything beyond that will require servicing. One could oppen the unit and look for bad solder or cracked board NEAR the power input jack.

OFTEN the power connector in the synth get broken from the circuit board connections.

ALSO verify the adapter is actually putting out the correct voltage or slightly above it..

Check the power adapter for proper voltage. Anything more will require taking it in for service.

Sir, This jack installs on most Casio keyboards to replace broken ones-a common problem. Often the broken jacks have the center connection pin ripped out or loose when the power cord cable has been pulled with a vacuum cleaner or yanked by a pet or child.

A technician is recommended to replace this part on your Casio instrument.
check with site www.keyboardstoday.com
Thanks Good luck

Try plugging in a set of head phones , if you get sound that way the input jack may be causeing the prob. try pulling it back an forth a few times, sometimes this will free up the head phone jack. I hope its that simple . May be some one will have another idea Good luck DFD please rate me TK U