A friend pluged in a higher voltage adapter then 9volts and heard a pop when when the power was turned on to a yamaha psr-175 keyboard.so would anybody have an idea of what might have popped.

Hopefully just a fuse. It could have been just about anything though. If you take it apart, there's probably a fuse right near where the plugin port is for the power adapter. But check any and all fuses you can see. Usually it's pretty straight forward to replace one.