I recently acquired this DSP and I'm doing the initial setup.
Only two speakers are attached at this time - Wharfedale Diamond 10.1 (6 Ohms) connected to Main A.
When I press the power button the unit turns off straight away.
According to the troubleshooting section of the manual this should be remedied by changing the Impedance Selector switch, but this makes no difference.
In diagnostic mode not all of the receiver is turned on. Seems like the unit goes into protection, Since it won't come on in normal mode without anything connected the problem is internal. Could be a bad amp or processor chip, Hope you can return it since it would probably not be a cheap repair. If it was the processor then the part is likely no longer available.
Update - I found the Service Manual and following instructions was able to power up in Diagnosis Mode (nothing connected - no inputs, no speakers).
I was able to power on and off several times without problems.
Connected digital inputs (1 x Coax and 1 x Optical), front and centre speakers and it wouldn't power up.
Disconnected inputs and speakers and I am back where I started from (unit turns off soon after power is turned on)