Two months ago I bought a NUC6CAYH to use as a small home Linux server. It worked without any problems. Of course, it is running without any monitor.
Today I have got another, identical NUC6CAYH from the same dealer, and I had him put in exactly the same RAM and HDD. And I installed exactly the same Linux version, even the HDD partitioning is the same.
When I disconnected all the peripherals, including display, the NUC immediately froze. I was logged in at the moment and my connection went dead. Reconnecting the perihperals did not help. The display indicated no signal.
After some experimenting I discovered, that the problem is with the display. The NUC has two ports - HDMI and VGA, which behave exactly the same. To boot the NUC a display has to be connected to either of these ports. Disconnecting it immediately freezes the system. The same holds for HDMI and VGA, there is no difference. Meddling with BIOS settings did not help.
When I reconnected the display and restarted Linux, I could see message like this in the syslog (:beta is the hostname)
2020-01-20T15:52:20.338794+01:00 beta kernel: [ 2.468039] BERT: Error records from previous boot:
2020-01-20T15:52:20.338795+01:00 beta kernel: [ 2.468041] [Hardware Error]: event severity: fatal
2020-01-20T15:52:20.338795+01:00 beta kernel: [ 2.468043] [Hardware Error]: Error 0, type: fatal
2020-01-20T15:52:20.338796+01:00 beta kernel: [ 2.468045] [Hardware Error]: section type: unknown, 81212a96-09ed-4996-9471-8d729c8e69ed
2020-01-20T15:52:20.338797+01:00 beta kernel: [ 2.468046] [Hardware Error]: section length: 0x290
followed by some memory and/or registers dump.
I have never seen such behavior. It looks as if the whole video card had gone away upon disconnecting the display. I could get a dummy VGA plug, but I suspect the NUC has a serious hardware problem, because the fist NUC6CAYH I bought last year runs without any problems and does not exhibit anything like this.
Is there anything I could try before returning the NUC to the dealer?
Both NUCs use legacy boot. I don't know the BIOS version of the first NUC bought last year, because it is in my parents' place. The second, faulty NUC report the following version:
The second is bios 0063. Find the bios version of the first.
Also, I would be using UEFI boot on BOTH. You may be experiencing problems with legacy boot.
I would also make sure both are on bios 0066. Make certain you "F9" after updating the bios on both machines to set defaults.
I updated the BIOS to the version you had given me the link to. Did not solve the problem.
Next I tried to reinstall Linux in purely text mode. My hypothesis was that linux with a console in some high resolution mode did not like it. I did manage to boot this text mode linux without a connected display. But when I disconnected the keyboard the system froze again. Another boot without any peripherals - successful. I manged to log in over network via ssh, but it worked for about one minute. Then it froze. Next attempt to boot - unsuccessful, the HDD had almost no activity. Last attempt - successful, but the system returned just few pings before dying off. I had no time to log into an inspect the syslog.
I may give a try to UEFI, but I am staring to believe this device is a real peace of junk.
Finally I gave up. Now I cannot boot the system at all, even with connected peripherals. It freezes randomly and the screen goes black. Sometimes even the HDD led stays permanently lit. I am returning it. Thanks for all your help.
Sounds like whatever is wrong with this box is getting worse and worse. You likely should get it replaced, preferably by the dealer if you can.