It's most probable that you've just blown the fuse in the internal power supply.
Typically they look like this immediately after the power in socket..
Look for the big capacitors and possible other components like diodes and chokes.. the fuse is likely there..
Probable that the fuse is a push-in fit, sometimes they are hardwired. In all circumstances replace it with one of equal value. If it's not written on the fuse ends then it's possibly written on the circuit-board itself..
Maplin of course for parts..
IF by chance the fuse isn't the problem, then a blown diode or something in the first part of the power circuit is probably gone, fear not, any good amp technician can find and probably sort it for you. Someone who works for a music ship doing keyboard or amp repairs should be able to sus it out..
