Inconsistent POST While Breadboarding

[matthew_w_frank]

New build minus a used motherboard (accidental purchase, sigh). I have worked through the troubleshooting thread (http://www.tomshardware.com/forum/261145-31-perform-steps-posting-post-boot-video-problems).

Currently I'm breadboarding it so it's just:
CPU / MOBO / RAM, with CPU fan hooked up and power to the MOBO + CPU.

SPECS:
CPU: i7-6700K
MOBO: ASUS Z170-A (USED)
RAM: Corsair DDR4 2133
PSU: EVGA 650 SuperNova G2

PSU: I have not tested the new PSU. I can swap it out for a known good PSU if people strongly suggest it. But, since I work from home having 1 machine up at all times is desirable, so I haven't yanked a known good PSU from another system just yet.

POST is inconsistent. sometimes no POST at all, sometimes it stays on the CPU, sometimes on the RAM, and then it'll get to BOOT device 5 times in a row - and then go back to not working.

At one point the system was working with a full build - maybe for a week. Boot was inconsistent and I often fought system freezes on boot, but if I could the system running it was stable. Eventually it just stopped booting. I swapped out the RAM because I was running DDR4 3000 with an i7-6700K and while XMP should make it simple stupid I figured I'd tried DDR4 2133 (which is what the 6700K is rated for) - but plopping in the new RAM did not resolve the issue.

Suggestions? Test the PSU? Just swap out the MOBO for a new one? If the system ran for a week it's probably not CPU related, but RAM/MOBO might be a good bet - correct?

Updates:

- Used a known-good PSU, no change
- @barty PSU is a EVGA 650 SuperNova is a G2, 80+ Gold Cert'd
- @barty cleared the CMOS, ensured no bent pins
- @barty 1 stick RAM right now, just to test POST
- @barty MOBO was second-hand via Amazon. It sucks, I intended to buy new, but Amazon makes it easy to accidentally buy used.
- @smorizio - bios bug?
- @smorizio - I've pulled the video card, it's just MOBO / CPU / 1 stick RAM right now

 

[Barty1884]

Can you post the full spec you're troubleshooting with?

 

[matthew_w_frank]

Barty, I've updated the post to include them, but here they are as well:

SPECS:
CPU: i7-6700K
MOBO: ASUS Z170-A (used)
RAM: Corsair DDR4 2133
PSU: EVGA 650 SuperNova

 

[Barty1884]

What does the RAM config look like? 2x4GB? 1x8? 1x4? etc.
It's worth checking with a single module (if you haven;'t already).

Beyond that, clear the CMOS and ensure there's no bent pins on the CPU. But if you've followed the "no post" thread thoroughly, you've probably tried that already?

Where did you acquire the Z170-A used? Was it a refurb? Or an open-box? Or just a second-hand, used board?

Boards that have been RMA'd/refurbished are always tricky.....as there was a reason it was sent back to begin with.

Which SuperNOVA 650? G2? Gs? NEX? etc. There's a range in quality there, although not likely to be the cause of any issues here.

 

[smorizio]

has the mb have the newest bios file to rule out bios bug. if you have a video card is the bios set to post from it or onboard video first??

 

[matthew_w_frank]

Updates:

- Used a known-good PSU, no change
- EVGA 650 SuperNova is a G2, 80+ Gold Cert'd
- @barty cleared the CMOS, ensured no bent pins
- @barty 1 stick RAM right now, just to test POST
- @barty MOBO was second-hand via Amazon. It sucks, I intended to buy new, but Amazon makes it easy to accidentally buy used.
- @smorizio - bios bug?
- @smorizio - I've pulled the video card, it's just MOBO / CPU / 1 stick RAM right now

 

[Barty1884]

No bent pins, quality PSU and not posting with only the bare minimum? Honestly, I think it's time to look at returning the motherboard.

 

[matthew_w_frank]

Thanks Barty. I think I'll take another look at the CPU / socket just to double check, and then I'll start hunting for a new MOBO, and maybe rail at that reseller on Amazon. I shoulda just sent the damned thing back as soon as I saw it was used.