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NZT48

PC won't boot after clearing CMOS while turned on

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System specifications: Intel i7 3770K / i5 3570K CPU, ASUS Z77 Sabertooth / MSI GD65 Z77 thing motherboard, 2 x 8GiB DDR3 RAM, ASUS GeForce GTX 1070 OC thing, Corsair AX860 PSU

Problem: PC turns on briefly, lights light up, fans spin up. After a few seconds it turns off then after a couple of seconds it turns back on, etc. There is no display.

Probable cause of problem: The CMOS was cleared while the computer was turned on.

What I have tried: I tried a different and much more powerful PSU, I tried taking the video card out and using the on-board video, I tried taking the RAM out, I tried another motherboard, I tried another CPU.

Any help would be greatly appreciated.

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Is it possible I originally killed the CPU and then when I tried the CPU in the replacement motherboard the CPU killed that motherboard?

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The common advice is that setting the clear CMOS jumper or hitting the button while the thing is powered on is bad, though they don't say why.

IMO could be that it's damaged the SMC or some other component/s but I doubt the graphics card, RAM or CPU has suffered, more like a motherboard component.
You could examine the board for shit-stains.  I'd try powering up without the coin battery and ensure the clear settings jumper is set to "normal" (that's another thing, in some cases having no jumper can cause problems).

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SMC  - System Management Controller.  Or equivalent.  Generally they sit there on standby current or using microamps on a laptop - they do stuff like power the system on, resume from sleep by lid opening etc.

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I've never cleared the CMOS while the PC is running, I don't want to find out either. I guess I know what to expect now ...

 

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I think I've got a P4 board that could be a sacrificial testbed but I suspect the result wouldn't be an indicator of what to expect with every board.

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On 9/15/2018 at 9:01 PM, NZT48 said:

: PC turns on briefly, lights light up, fans spin up. After a few seconds it turns off then after a couple of seconds it turns back on, etc. There is no display.

How many cycles have you let it go through? With modern UEFI systems a bios change or bios reset can make the system do a boot/reboot multiple times as it updates system parameters. However if it's doing the reboot past 4 or 5 cycles something is probably screwed or set wrong.

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22 hours ago, aliali said:

How many cycles have you let it go through? With modern UEFI systems a bios change or bios reset can make the system do a boot/reboot multiple times as it updates system parameters. However if it's doing the reboot past 4 or 5 cycles something is probably screwed or set wrong.

I reckon it has gone through at least 7 cycles.

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Hmm,

 

Whilst as Ry says you should never reset CMOS with power on, in fact the PC should not just be off, but unplugged as mentioned here in several ways to rest CMOS:

https://www.lifewire.com/how-to-clear-cmos-2624545

However you MAY get away with it, but I'd personally never try it, doing so interrupts a process that has done it's primary job, the BIOS, and then is sitting in the background but by doing it whilst on you just lobotomised your computer.

However, I would doubt you actually damaged any components as such, unless you were not wearing a static strap and the jumper removal sparked the board - even then modern components are reasonably static tolerant.

You have a conundrum, it would be nice to flash the BIOS - not something I ever much like doing but you can't even get to the old BIOS to boot off a USB for example so that is out. The only option there is to buy a new BIOS chip, assuming the one on the board is removable, 50/50 on that these days.

One thing you have not mentioned is, after your foobah, did you replace the jumper? If you did not then most boards will go into a reboot loop something like you describe, the jumper is usually in series with the circuit.

I can't make any comment about the PSU or MOBO replacement - that's the two cores of a new system so something is decidedly odd unless you were reckless and installed all your RAM and add on boards instead of doing a bare bones boot. If you did then pull them out back to minimum RAM and you may be on the trail of a culprit component.

It's a lesson for anyone wanting to put CMOS back to default via the jumper, NEVER do it powered on and unplug it as well and leave it a few minutes - on the rare occasions I have needed to do it using the jumper, the BIOS default setting usually is fine, I have even unplugged the PSU, power capacitors can hold a charge for many hours.

I suggest you are probably somewhat out of your depth, but go back to basics, that is the essence of troubleshooting, original board, minimum ram, no add on cards, don't even install a boot drive, if the BIOS starts and you get to boot drive fail then you are ready to go forwards, and, make sure the jumper is installed, correctly ?

 

Cheers

 

 

 

 

 

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