Hi @darronkeit80141
Could be that the power button is faulty.
Here's the [https://elektrotanya.com/yamaha_psre303_sm.pdf/download.html|service manual] for the keyboard that may help.
Below is an image taken from the manual showing the power supply input circuit that may also help if the switch is OK.
If the switch is faulty search online for [https://www.google.com/search?client=firefox-b-d&q=WD893400|WD893400]¹ (supplier examples only) to find suppliers that suit you best.
¹ This is the Yamaha part number for the Standby/On switch - see Parts List section in the manual, p.3, part #40
[image|3464039]
(click on image)