Upgrading CPU's Riser board throws red LED after installing X5690
I upgraded my Firmware to 5,1 on a 2009 MacPro. The computer boots fine with the dual quad core processors. But when I install the X5690 3.46ghz chips - it throws the red led and doesn't chime post, no video (page 34 of the MacPro early 2009 manual).
I have tried booting with different OS versions, tried a second Riser Board, reset smu. Confirmed boot version B03.
I have put the X5690 in a single core Riser Board and it boots fine.
Could it be the chips don't work as pairs?
This was supposed to be attached