Thank you for welcoming me on this forum. I have a Psr E443 Keyboard. When you switch on it plays only for 3 minutes & cuts off but display remains on but no sound. And it can't go off on the switch button.
Sounds like (sorry bad pun) it needs opening up and testing of components and connectors cleaning and reseating, if you are a good DIY person with electronics. It is not likely cost effective to have it looked at by a Technician given its age.