I am fighting an odd issue in one of my Z400s.
It turns itself off periodically and the beep code indicates "power failure" -- four beeps.
First time I have seen this and it NOT be a power supply (changed PSU already).
So I removed two out of three 1070Ti cards -- running it on just one for at least 24 hours to see if the issues persists. Then I will add cards back one at a time if it does NOT persist on the single card.
I also re-pasted the chipset heat-sink as that seemed to be running a bit hot (just in case).
If all else fails it may be my first case of actual Z400 hardware failing (maybe motherboard).
I only have two Z400's mining with Vega 56's so my sample size is small. One Z400 with two Vega's and the other with one Vega.
During an internet outage I powered down all my miners including the Z400's. When the outage passed I powered on all miners and started them mining.
All systems came back on except for the Z400 with the single Vega. It too had the "Red Power Button" flashing and four beeps. In researching, this error is supposed to be GPU initialization failure. I tried everything (replace power supply, ran memory tests, swapped to known good GPU) and the problem persisted.
I ended up putting the Vega 56 in another system which works fine with the power supply from the failing Z400.
So the issue defiantly is with the Z400 motherboard. I ended up scrapping the Z400.
I tracked my issue down -- and it ended up being one of the GPUs in the system.
After some other swapping of hardware re-including that GPU would actually result in the 4-beep code immediately upon pressing power on.
So far good to go for 24 hours.
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UPDATE (6-22-18):
You may be right, actually, MinersRus! Another day of running and the 4-beeps repeated.
I am going to order a few spare motherboards on e-bay to keep on hand. That is the only thing left it could be.
I have seen similar issues with systems that are powered 24/7 that really aren't meant to be. If the capacitors for the on-board regulators are not of high quality then over time they swell up and sometimes even leak their guts.
I have a Windows 7 desktop computer that runs 24/7 as my home DVR. It is running the Free Windows Media Center. I have had to replace the motherboard once already because of bulging capacitors. Then the replacement motherboard began to have issues. Since I now knew the problem was capacitors I replaced the ones I found bulging which fixed the problem.
Going back to my failing Z400 the reason it failed was when it got powered down the capacitors had pressure reduced because of no power. The constant pressure then no pressure is what caused it to open up and thus lose it's value causing incorrect power on the motherboard.
Because of this issue you may need more than a few Z400 spare motherboards. If a time comes when you have to power off your Z400 miners a number of them may not power up again without issues.