Zeppelin Air Powers on and buzzes for 10 seconds then turns off.

I have looked into this and the psu appears to be OK. There is 5v on the standby supply and + - 18v on the amp main supply rails.

But as soon as you turn it on there is 18v dc across the sub woofer terminals. After a few seconds the amp protection kicks in and turns the unit off

I think this is a known fault with the d class output stage for the woofer. But whilst I can find a lot about the Psu I am struggling to find info about the amp.