Vega64 ether problem

Hello,

I have a problem with 2 Vega64 rig. While it was mining XMR it did without any problems (1400/1100/950mV). Now I switched to ETH (claymore 15)and can’t get them to accept any OC. As soon as I try to configure any OC (cpu, mem, voltage) Vega’s stop to mine or go down to 7MH/s. Without any OC they mine 38MH/s but with 680W!

Any idea, any help…