It's an external power supply, yes?

When you replaced it, did you get a Yamaha, or some generic? (It IS the correct amperage and voltage, yes?)

If not, get a REAL proper PS

If you wiggle the power cord while you are playing normally, does it power down or re-boot?

If so, replace the PS or solder a new plug to the end (and cut off 2 or 3 inches to get rid of stressed wiring)

Try to replace with a power supply with the correct voltage and polarity, but maybe 30-50% MORE amperage (this will help during extra current load while the Floppy spins up.......), this will not hurt your keyboard, whereas too little amperage WILL.......

If it only re-boots with certain disks and not others, use a computer to copy the SMF to a fresh disk and see if it still reboots.

If it still reboots only certain SMFs after a copy to a new disk, it's a corrupted SMF. Try loading it into a computer sequencer, look for any wierd sys-ex or controller codes the PSR doesn't respond to, and delete them, and re-save it.

Hope this helps......