iMac A1419 emc 2806 no diagnostic Led lights on

Hi

I have an Imac A1419 emc 2806. It won't turn on.

Don't know what happened to it. Saved it from going in a bin.

Here is what I have found so far.

There are no diagnostic LED lights on at any time.

The on/off button works and has resistance

The PRAM battery has been changed (had 2.8v)

The power cable works.

I have power up to LED light 1 but its not on.

Found nothing when searching for any burnt out components or water damaged areas.

I would like to try avoid throwing parts at it and try to fix the issue if it is the motherboard or power supply board first. The trouble is trying to find any shematics or information on the bloody thing. If anyone could help me out there would greatly appreciate it.

What I would like to know is what the voltage readings should be from the power supply to the logic board at each terminal.

Thanks