Its possible to repair but its not a swap the fuse out type job. you need a board solder and access to proprietary parts.

If you want to ensure that the problem is the turn on circuit, first check the outer power fuses, then open it up and trace the remote lead until it reaches a small black chip. That chip will have several outputs that check for protect mode conditions before sending power to the transistors that supply power to the amp circutry.

Check that you have power at the lead that supplies power to the circuit.
Check that there is continuity between the RCA points and the 1. parallel resistor across the leads 2. the choke coil(spooled wire around some type or core) and to the RCA plug.

Also check the primary choke coil which is really big copper coil of wire that filters noise from the power line - they vary as to their configuration so I couldnt tell you what to look for.

Ensure there is NOT continuity between the gnd and the RCA leads pos leads.

Back to the turn on circuit:
Check each terminal - there should be one lead that shows 12v to the turn on relay(usually a transistor to prevent noise), the rest should have either no power or consistent voltages as they are protect mode leads.

As you can see its not an easy process to diagnose board problems and this barely scrapes the surface.

Some amps such as newer JL and the kenwood SX amps even have binary turn on signals which cannot be read with a multimeter. Your best bet is to send it in under warranty.