Replaced power supply but still not working?

My iMac would not power up at all. I heard power supplies were a common issue with intel iMacs. I purchased a new power supply and replaced. After successful reassembly, iMac still does not power up. I disassmbled again to investigate. While I had the iMac open (taken apart) I tested the AC inlet with a multimeter and got the correct voltage reading. I then connected the AC line voltage to the power supply and tested the DC voltage out: good reading. I did this test on both power supplies with the same results. The power supply is not the issue. I would appreciate any suggestions to what the next step could be in the the troubleshooting process.

I took it to an apple specialist who determined it is a bad logic board...

Thanks for your help!