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Ok, this is long and very puzzling. I've built a couple of systems and am a computer engineer so I thought I understood these things, but I am stumped at what to try next.

Short story: breadboarded brand new motherboard with brand new CPU does not POST, boot or beep. And I've tried everything, including replacing every component including PSU and clearing CMOS.

Long story:

It started with what supposed to be a high-end gaming rig. i7, water cooling, M2 etc. After putting everything together it didn't boot up, so I started to remove components, even tried with a spare i5 I had. Fans spin up, MB LEDs light up, but no boot or POST.

Breadboarded (put only motherboard, CPU, fan and memory together outside of chassi) but still nothing. Attached a chassi speaker, but no beeps, not even without memory.

Returned motherboard (Asus Prime H270-PRO), came back with one bent pin fixed (but they couldn't tell me if that was on the board or in the socket) but with "OK working" from them. They even upgrade BIOS.

Full of hope, put back the i7 (7700). Still the same, fan and LEDs turn on, but no boot, POST or beep. Swapped to the i5 (6500). Same thing.

Tried another PSU (from my day-to-day computer, so I know it's working). Still the same.

Gave up, got another motherboard, and just to be sure, a brand new Celeron G3900, in case the two other CPUs got fried by the first board. Breadbording this motherboard directly with the Celeron, attached the ATX and CPU-power lines from my new PSU, outside of chassi.

NOTHING! Still not even a beep...

The new board is Gigabyte GA-Z270P-D3. It spins up the fan, rew's it a few times, settles on a moderate speed for a few seconds, then turns off. Repeats this sequence over and over.

Tried my other, working, PSU, still same. Cleared CMOS, still the same.

So it seems like no combination of two motherboards, two PSUs and three CPUs doesn't even get to POST...

Is it possible that the problem with the first motherboard (bent pin?) fried my to CPUs and broke the PSU so that it in turn broke the other motherboard?

I haven't tried the i7 or i5 in the second mobo, since I'm afraid that they could damage this board if they are bad, I wouldn't think so, but I'm starting to doubt my senses here.

Question 1: What does the cycling of the fan speed on the GA-270P indicate? Malfunctioning fan header? Tried one of the other original fans, so it isn't that.

Question 2: So, is there a scenario where the two CPUs were fried by the bent pin (assuming it was in the CPU socket)? And could that have broken my new PSU so that it in turn broke also the new motherboard?

Question 3: Can I safely put one of the first CPUs in the second board without risking that board to go bad too (assuming it is not bad already)?

Question 4: Am I missing something else, really fundamental?

EDIT: Progress on this have been slow due to other commitments, but it turned out that the second board also had bent pins (Is it me? Starting to doubt my abilities...). So we know nothing about the state of the processors. Might still be that the first board is still not working, even stated so by supplier after "fix". Next step, send back board with CPU:s if supplier accepts our claim, or by another motherboard... Sigh...

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  • It shouldn't have fried the PSU, if you suspect PSU damage check the 12v 5v and 3.3v rails with a digital multimeter when you have it powered. I agree that it is strange.
    – Tim_Stewart
    Commented Feb 25, 2018 at 21:42
  • 3
    When you run a computer without a case it's called "Benchtesting" not "breadboarding". This is a breadboard: en.wikipedia.org/wiki/Breadboard
    – HackSlash
    Commented Mar 1, 2018 at 23:12
  • 1
    This is how you benchtest: thenerdbench.blogspot.com/p/bench-testing.html
    – HackSlash
    Commented Mar 1, 2018 at 23:13
  • Is there anything underneath the MB that could short out the board? A screw or any other conductor that could be contacting the MB?
    – HackSlash
    Commented Mar 1, 2018 at 23:16
  • 2
    Yeah but a breadboard is a real thing in electronics and we already use the word "benchtest". Let's use unambiguous terms that are generally accepted.
    – HackSlash
    Commented Mar 1, 2018 at 23:29

3 Answers 3

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+50

The scenario you outline, where a bad motherboard has fried two CPUs, is a bit far-fetched, but stranger things have happened.

Your testing seems to have shown that the PSU is not the issue, and this is also indicated by the fans starting up correctly. The lack of beeps is the most puzzling and seems to indicate a very early problem with some components, but can also serve as a diagnostic tool. (Hopefully the beeper has not been disconnected by mistake.)

I suggest to do the following :

  • Power up without RAM at all
  • If you now get beeps, then this is a RAM problem - insert the sticks one by one to locate the bad one, or check their compatibility with the motherboard.
  • No beeps mean deep problem with MB or CPU, but the RAM is not involved.
  • Follow this tomshardware troubleshooter for further analysis. Post the results even if nothing conclusive is found:
    PERFORM THESE STEPS before posting about POST/boot/no video problems.

If you still cannot find the cause, I would send the motherboard with both CPUs to the motherboard manufacturer and let them know that you suspect that the motherboard has fried both of them before it was repaired. Let them sort it out, and in case the CPUs are fried demand their replacement. Check very well all cables and connectors before sending, to avoid them answering that all is working correctly and the problem is on your side.

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  • Opening a support ticket with the manufacturer is the correct answer but you can't send in other hardware with an RMA. If you mail your CPU to the MB OEM you won't get it back. It always says so in the fine print.
    – HackSlash
    Commented Mar 6, 2018 at 17:09
  • @HackSlash: If that's the case for the poster, perhaps he could get a written exception to the rule. His best solution might be to test the CPUs via a workshop that would have other test methods than plugging a bad CPU into a good motherboard.
    – harrymc
    Commented Mar 6, 2018 at 17:16
  • Thanks @harrymc for adding the comment on the beeper coming lose. But already checked, re-checked and re-re-checked...
    – thoni56
    Commented Mar 9, 2018 at 10:02
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Q1 Answer

The PC is rebooting as it cannot get a response from the CPU.

Q2 Answer

The CPUs can be fried, but any modern PSU will shut-off if it detects that its damaged.

Q3 Answer

I wouldn't. The bent pins on the first MB can damage the CPU, which in turn can damage the second MB (if the bent pins were on the CPU socket, otherwise go for it!).

Q4 Answer

Even the most seasoned enthusiast makes mistakes. Have you checked that all connections are firmly secured? Have you also checked compatibility?

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4
  • Are you sure the memory modules are good? compatible with your rig?
    – ttaylor1218
    Commented Mar 2, 2018 at 3:34
  • Comes under Compatibility @ttaylor1218
    – Ultrasonic54321
    Commented Mar 2, 2018 at 8:01
  • Trying to boot without memory to get beeps....
    – thoni56
    Commented Mar 2, 2018 at 22:11
  • Let us know if any updates arise.
    – Ultrasonic54321
    Commented Mar 2, 2018 at 22:16
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After a long while we invested in another motherboard, one that sported LEDs for the POST sequence. And when we started that, lo and behold, it stopped at the memory LED.

So, encouraged by some progress, we bought new memory. With that installed the new board started up, no problem. Furthermore, so did the original board.

We also tried the three processors we had, and they all worked. And so did the original, repared, motherboard.

So, the problem was the memories. No wonder there was no difference between having memory in or not. Probably the bend pin on the original board fried the memory sticks. Don't understand why there was no POST beep, though. Could have been the beeper as indicated early by @harrymc (but it did work on other computers...).

LESSON LEARNED: always swap all parts with some alternate ones. If we've had some extra memory from the start we could have saved a lot of time, money and frustration. Buying a single stick of some cheapo memory early on would have shown the problem.

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