With the help of others and the Apple service manual, I have been trying to trouble shoot. This includes swapping A and B CPUs, going back to my original CPU, only using CPU-A, using only 2 good RAM sticks, cleaning and reinstalling the Northbridge, removing and cleaning the PSU, etc.
In following the service manual, I got the right diagnostic lights on the backplane when the CPU tray was installed with no CPU or heatsink (e.g., PSU, 5V STBY, EFI_DONE and GPU_OK). However when one CPU was installed I get lights in the attached picture.
I again removed the CPU and noticed some slightly bent pins, so I straightened those out and tried again. Same... no chime, no screen image. I cannot find advice as to what this series of lights mean, so if you have an idea, please help.
Note, there are no unusual RAM or CPU LEDs on the CPU tray.
Thanks for your help!