You wil be lucky if it is the CPU board, cause with some luck you can find a replacement.
The symptoms you described makes me think of a dead board OR CPU card.

In the case of a dead board, a common issue is the dead Marvell Discovery II MV64361 Northbridge.

At least this was the case on my case. Cause I had two dead Pegasos 2 in total.

Perhaps you could be lucky and the case is the CPU module. In that case, yes a replacement Module would do the trick. Try to find one and check with your existing board.