I really need help with my psr-s670.

I bought a new Yamaha PSR-S670 and used it for a few months after which I noticed that when I turned on the power, is will show an error "Internal Hardware error!", all the lights on the buttons will turn of but no sound is produced. if I leave it for a long time and reboot again, it will clear and work normal.

I have tried factory reset and did not solve it.

After a while, the error dont clear any more. i have seached everywhere on the internet for solution and have not found one.

Can someone assist with any solution to this error?

Thank you.