I have recently had a bad experience with a brand new NUC5CYPH. In summary:
I added the RAM and SSD, and installed Windows 7. I was most of the way through downloading and installing about 200 updates when the machine started to behave a bit erratically: 100% processor use while simply searching for upgraded using Windows update, and very high RAM use, too. About an hour later I got a BSOD with random white dots all over it. When I tried to re-boot the NUC it simply power-cycled every few seconds (cooling fan switching on and off) without ever reaching the POST screen. At this point the NUC had been powered up for maybe only 8 hours total.
There was no video output from VGA, or at least nothing my monitor could display. My monitor was detecting a signal and momentarily showed the selected resolution and refresh rate, but this was displaying nonsense (refresh rate of 11Hz instead of 60Hz). I have two VGA inputs on my monitor and both gave the same result. So far I have not been able to try it on another screen.
I removed the RAM and SSD and tried to boot from there, but I got the expected "three flashes" from the power light, indicating that there was a problem with the RAM. When I re-inserted that module, the original symptoms came back. At this point I decided it was dead and boxed it back up ready to return to the supplier.
I have since found that the RAM module I bought, while it does meet the physical and electrical requirements of the NUC, is not on the approved list
The RAM I bought is here https://www.scan.co.uk/products/4gb-(1x4gb)-corsair-ddr3l-so-dimm-value-select-pc3-12800-(1600)-non-... https://www.scan.co.uk/products/4gb-(1x4gb)-corsair-ddr3l-so-dimm-value-select-pc3-12800-(1600)-non-...
My question is: Could the "non-approved" RAM module I bought have been the reason my NUC failed so early? I know that the NUC is supposed to tell you if the RAM isn't electrically compatible, and will refuse to boot, but I had no problems whatsoever until the BSOD.
Who says your NUC has failed? You haven't done enough to prove it as yet. It could still be the DIMM that is responsible for what you are seeing. Until you try it with another DIMM, you won't know...
Oops, I didn't answer your question. Modules not being on the approved list does not mean they are bad or can't be used; it just means that Intel has not tested them.
Yeah, I kind of felt a bit daft asking I guess a better question could be "would any suspect RAM module make my NUC fail".
My logic for assuming that it is the NUC itself that has failed is that if it was a bad RAM module then the NUC would be smart enough to diagnose it and I would get a flashing power light error code during power up. As I mentioned in my first post, this does happen if I remove the RAM altogether.
So do you think a bad RAM module could prevent POST altogether, and cause the power cycling, as I described?
Unfortunately, bad DRAM modules can manifest in a number of ways. It may simply not work at all, in which case the module might detect that the module is not present and the three-beeps will result. It may fail initialization and immediately lock up the memory bus. While the BIOS has a watchdog timer to recover from this situation (and will attempt to do so automatically), it can only back off the configuration so far before it might have to give up. It may seem to pass initialization but accesses to the memory fail (and, unfortunately, this may take time to result). In this case, if the bus ends up locking up once Windows starts running, the watchdog timer going off is going to result in an immediate system reset. Otherwise, the running software (including POST firmware) could go off into the weeds and hang the system completely. It may pass initialization but accesses to certain addresses (or address ranges) will fail. If this results in bus lockup, it will result in an immediate system reset. Ok, my hands are tired from typing; there are all sorts of other situations I haven't gotten to. Suffice it to say, if *can* cause symptoms like you are seeing. As I said, get another module to test it with. Don't purchase just yet; borrow one from a friend or have a store or repair shop test it with another module.