Kenwood KR-V5090 - Stuck in 'Protect Mode'?

I have a Kenwood KR-V5090 Amplifier with built in radio. Following a power cut last week, when I power it up, it constantly goes into 'Protect Mode'

This means that the display blinks 3 times (as it would anyway), then shuts off, at which point the standby light starts flashing.

I have unplugged the speakers (the protect mode is, apparantly for a speaker short), and have unplugged everything else. No change.

Any ideas?

Mark
September 2008