Question Build won't POST, how to verify it's the CPU

Aug 1, 2019
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I have two homebuilt computers that we use in my lab that stopped working. First they occasionally blue-screened, but then got to where they wouldn’t even POST. This happened about a year apart at the same station.
I later learned that there was a faulty UPS there backing up the PC power supplies that used to flicker and frequently brown out and black out. I have been trying to get one of the builds working again and have not had luck.

Motherboard: ASUS Rampage V Extreme.
CPU: Intel Boxed Core i7-6850K Processor (15M Cache, up to 3.80 GHz) FC-LGA14A 3.6 6 BX80671I76850K
RAM: gskill ripjaws v series 16gb ddr4 (2x8GB) F4-3200C16D-16GVRB
I also have cooler fans, a graphics card, SSD, and optical drive. However, I’ve stripped the build down and still had problems, so I don’t think any of those are the issue.

I did the typical check of all connections, reseated and used compressed air to blow off all connections and had no luck.
I replaced the RAM with new RAM with no luck.
I stripped the build down to CPU, cooling fans, and power supply but still couldn’t get it to POST. No digits, no beepcode (I have the beeper plugged in), just fans and lights would turn on. The CPU indicator light is also on.

I tried clearing the CMOS with no luck. I also tried the second BIOS and tried flashing the BIOS.
We had a third motherboard around, we had bought it used but not used it before. I swapped it in but still had no luck.
I replaced the power supply units with Seasonic FOCUS 750W Gold in case the PSU was bad. The PSU was working on another similar build so I know it works, but it still did not fix the problem.
At this point, I feel like the only thing left to try is replacing the CPU. I’m hesitant to buy a new CPU unless I know it is going to fix the issue.
So at this point I have three main questions.
  1. Can frequent power interuptions cause the CPU to fail in this manner?
  2. If somehow all 3 motherboards are just bad, will taking a good CPU from a working setup to test it here put that CPU at risk? In other words, should I swap CPUs around between the working and not working setups to test things or is this risky?
  3. Is there anything else that I need to try?
 
Aug 1, 2019
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Are you sure the monitor/ cable you are using to see if it posts is working?
I checked that early on, yes. Currently, I'm testing without a monitor but was previously using working monitors. Right now I'm watching for startup codes on the 2-digit display built into the motherboards and trying to get some beepcode.
 

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