I got another Question. Can hashboards get too cold ?  Its 12 c° / 54 F now in my area. The big fan blows air from the outside directly inside to the miner inlet fans. After I let one miner blow up the hot air in the one miner with the Issue, the chains came back. 

Thanks for your help guys. I do the troubleshooting as you said. The Power_Lost passed away ( I have no clue how) but I found out that the hashchains maybe caused this error. I put the chains in another working Miner and found out that all three hashchains were dead. 1-2-3 0 Asics 0 Asics and 40 Asics. I had to contact the seller, I bought them used and this one never works good from the beginning.

Thank you and keep the good work up, other miners needs your help too  

Hey guys,
I Need help with my Antminer S17 Pro. After it tries to set the Voltage to 21.0 V it puts out the Status: Error_Power_Lost. First I tought it is the PSU. But after running it with another the problem is still the Same.
What can I do to find the Issue ?

Thank you