Error code VLT0204 on a Poweredge R720

Hello,

     I picked up a server recently and have been trying to diagnose its problem.  I have error code VLT0204 "the System Board fail-safe voltage is outside of range" and a 2cpu configuration in a C4B3R motherboard.  Some things I have tried:

• Reduce server to minimum configuration (same error occurs)
• Swap power supplies out in minimum and fully loaded configurations (same error occurs)
• Remove all swappable drives (same error occurs)
• *Notably there is a green light on in the Riser 1 area of the motherboard (so I assume power is going there)

I'm thinking that there may be a short in the motherboard somewhere, and am wondering if I can get a detailed diagram of the motherboard to help diagnose where it could be. Or if there are any other tips to diagnose.

Thank you!