That would be a good guess.
If it's not the cpu, then it's the DC-DC converter that's mated to that cpu module.
Either way, you need to replace hardware parts.
Go to the Sun System Handbook and get the E450's Service Manual.
( actually, you might as well get ALL the documentation for the system while you're there )
http://sunsolve.sun.com/handbook_pub/Systems/E450/E450.html