PC doesn’t turn on after plugging in 8-pin CPU cable

[madsenmm]

I'm currently in the progress of rebuilding a setup, with combinations from 2 setups.
I read a ton of posts but not really gotten any further on this issue.

Currently the motherboard is out of the case, as I read breadboarding would be a good idea to rule out the case short-circuiting the setup.
I've done the paper clip on the PSU to rule that out, fans spinning as expected.

I've tested with only Motherboard, PSU, CPU, 1 RAM, and both with and without GPU.
Everything works as expected until I plug in the CPU pin.

I think I did a CMOS reset, by removing the battery from the motherboard.

One thing I'm a bit uncertain of, is when running without CPU cable, and the GPU is on, should I be able to see something on the monitor when plugged in? It just goes to blank, and says no device connected

Any help is much appreciated.
How does one test a motherboard in other ways?

 

[Toothless]

Have you done the normal troubleshooting steps? (Clearing CMOS, letting capacitors drain, different hardware, etc)

 

[madsenmm]

Have you done the normal troubleshooting steps? (Clearing CMOS, letting capacitors drain, different hardware, etc)

CMOS I did.
Tried different CPU cooling, RAM, and GPU. The motherboard is the main thing I haven't changed.

Can you elaborate on letting capacitors drain

Maybe I just fried the CPU, if at all possible?
I just did start up, i tried with another PSU, it didn't sound too good, and started smelling burnt.

Now the motherboard lights red on the CPU shortly, and shifts to yellow on the DRAM...

 

[Gungar]

CMOS I did.
Tried different CPU cooling, RAM, and GPU. The motherboard is the main thing I haven't changed.

Can you elaborate on letting capacitors drain

Maybe I just fried the CPU, if at all possible?
I just did start up, i tried with another PSU, it didn't sound too good, and started smelling burnt.

Now the motherboard lights red on the CPU shortly, and shifts to yellow on the DRAM...

He is talking about PSU capacitors drain. Just turn off the PSU and let it off during 1 hour and then try again.

 

[madsenmm]

He is talking about PSU capacitors drain. Just turn off the PSU and let it off during 1 hour and then try again.

Tried it, didn't work

I think the motherboard is toast.. When turning on power, both the CPU cooler and the Motherboard LEDs only show red lights.
Not the indicator lights on the motherboard though, just all the visuals.

Tested with another CPU cooler, in case the current were dead, same response.

Going to test with a new motherboard. But how do you actually confirm a motherboard is dead?

 

[Ferather]

How many watts is the PSU and how much power is needed? - "I tried with another PSU, it didn't sound too good, and started smelling burnt."

 

[RJARRRPCGP]

CMOS I did.
Tried different CPU cooling, RAM, and GPU. The motherboard is the main thing I haven't changed.

Can you elaborate on letting capacitors drain

Maybe I just fried the CPU, if at all possible?
I just did start up, i tried with another PSU, it didn't sound too good, and started smelling burnt.

Now the motherboard lights red on the CPU shortly, and shifts to yellow on the DRAM...

Sounds like all the signs of MOSFET failure. But I usually expect that on motherboards with inadequate MOSFETs.

 

[madsenmm]

How many watts is the PSU and how much power is needed? - "I tried with another PSU, it didn't sound too good, and started smelling burnt."

The original 750W, the one where it started to smell burnt, was 650W.

But only motherboard, 1 RAM block and the CPU Cooling when that happened

Sounds like all the signs of MOSFET failure. But I usually expect that on motherboards with inadequate MOSFETs.

Have seen that on a few posts, just seems unlikely as I understand.

guess I’ll have to pull out a multimeter and test

 

[Ferather]

I will quickly add my motherboard has 8 + 4 for the CPU, where 8 is enough without overclocking if I remember right.
Indeed I would do some power tests and see what you can find. Hopefully its a simple problem.

 

[madsenmm]

I will quickly add my motherboard has 8 + 4 for the CPU, where 8 is enough without overclocking if I remember right.
Indeed I would do some power tests and see what you can find. Hopefully its a simple problem.

My motherboard has the same connectors for the CPU, only using 8 of them. Same for the previous setup it was used in, where it worked.

Are motherboards really so delicate that a slight knock on it can kill it? I thought I was very gentle with it in the build process

 

[Ferather]

It used to be possible to bend capacitors and other connections, but current processes allow them to assemble them tight to the board.
Many years ago it would be possible to bend a whole group of parts when trying to attach the board or other.

I don't even think static is much of an issue these days as long as its a small amount.

 

[madsenmm]

It used to be possible to bend capacitors and other connections, but current processes allow them to assemble them tight to the board.
Many years ago it would be possible to bend a whole group of parts when trying to attach the board or other.

I don't even think static is much of an issue these days as long as its a small amount.

So just really unlucky with the board?
Still can’t make sense of the PC not booting at all with the 750W PSU. But trying something with the 650W

 

[Ferather]

If the board and its current bios supports the CPU and power requirements and the PSU's can supply that, then yes, unlucky indeed.

 

[madsenmm]

Going to try with a new motherboard and new CPU.

Not sure of the odds of the CPU dying just randomly, but didn’t expect the Motherboard either

 

[Calenhad]

Going to try with a new motherboard and new CPU.

Not sure of the odds of the CPU dying just randomly, but didn’t expect the Motherboard either

I had an Asus Crosshair Dark Hero X570 motherboard that just didn't boot one morning. One RMA later and everything is working again with a new motherboard. So the price of a product does not mean it is immune to sudden failures. This happened after about 6 months of normal use.

So the odds are higher than 0

 

[madsenmm]

I had an Asus Crosshair Dark Hero X570 motherboard that just didn't boot one morning. One RMA later and everything is working again with a new motherboard. So the price of a product does not mean it is immune to sudden failures. This happened after about 6 months of normal use.

So the odds are higher than 0

I have a slight idea where it might have gone wrong. I remember now that the old PSU i used in this new setup, weren’t the original cables that followed it as of new. I back then just plugged it in at reused all the cables already installed in the PC.

Now with the new motherboard I just hooked it up the same way, and figured that might have blown something on the motherboard.

 

[Bobaganoosh]

I have a slight idea where it might have gone wrong. I remember now that the old PSU i used in this new setup, weren’t the original cables that followed it as of new. I back then just plugged it in at reused all the cables already installed in the PC.

Now with the new motherboard I just hooked it up the same way, and figured that might have blown something on the motherboard.

Oh dear. Yes that is a major no-no. The power supplies tend to have different pin-outs even though they'll use the same modular connectors. I've seen a few people fry SATA SSDs like that, among other things. Hard to say exactly how many parts have been damaged at that point. You always want to use the power cables that came with each power supply.

 

[Toothless]

I have a slight idea where it might have gone wrong. I remember now that the old PSU i used in this new setup, weren’t the original cables that followed it as of new. I back then just plugged it in at reused all the cables already installed in the PC.

Now with the new motherboard I just hooked it up the same way, and figured that might have blown something on the motherboard.

That'll do it. Board is toast.

 

[madsenmm]

What are the odds that it worked on the other motherboard, been running with that setup with mixed cables for over a year.

and then just instantly kill a new motherboard?

 

[LabRat 891]

If re-using modular cables, always quadruple-check the pinouts with a DMM!

I recently re-used PCIe and CPU-EPS cables; if I hadn't re-pinned them, fireworks would've ensued.

 

[Pickles Von Brine]

That'll do it. Board is toast.

Yep. She is done Jim. NEVER reuse cables from other power supplies. Even between same brand different models (unless same model just more wattage). Corsair is the exception if it is ones using their own speced cables, IE if your power supply uses their P4 cables and your new one uses P4 cables then it is safe to reuse old cables.

 

[Mussels]

What are the odds that it worked on the other motherboard, been running with that setup with mixed cables for over a year.

and then just instantly kill a new motherboard?

Odds are, that you changed a cable over without realising - one unused cable on the old system that is used on the new one, that's enough to kill something without knowing.
It's not 100% certain death to mix cables as sometimes they're compatible - but it should never, ever be done unless they're from the same brand and clearly labelled (like corsair with their gen3/Gen4 labelling)

Everything works as expected until I plug in the CPU pin.

That's actually *nothing* working as in that situation except the PSU, the PC is brainless and inactive.

In case the cable issue has NOT the system and the parts are actually fine, let's cover some of the basics:

POST requires

1. Motherboard with BIOS that supports connected hardware
2. CPU supported by the board and BIOS
3. Ram supported by the CPU and BIOS
4. Graphics output of some kind
5. PSU with at least 20 ATX and 4pin EPS connected. Boards may want 24 and 2x8 EPS, but 20 and 4 is enough to reach the BIOS usually.

Any extras like a GPU or PCI-E card, even USB devices can screw with things and should be removed. Test out of the case on top of the motherboard box if needed, but do NOT use the anti static bag as those conduct electricity.


*ROG STRIX Z490-F GAMING requires bios 2103 for an 11900k, and shipped with 0403. Very unlikely that CPU will work on that board without it being manually updated.
The board supports USB flashback, so you can manually update it in it's current state as long as you can follow the instructions precisely - going off-script will not work, and you get no indication of errors when doing this.

1.You'll need a FAT32 formatted USB flash drive with the current BIOS file for the board on it (and nothing else)
2.Unzip the BIOS .zip file, extract all files to the USB drive.
3.Run the included renamer batch file, which renames the file to one the bios flashback for that board accepts
4. The Motherboard must have the power connectors for ATX and EPS connected, and have power. DO NOT POWER THE PC ON.
5. Connect the USB to the correct port.
Red arrow is the port, red circle is the flash button, blue arrow is the LED that should blink as this proceeds.

6. Press that flash button, look for activity on the LED and wait for it to finish. It can take several minutes depending on the speed of the flash drive, so give it 10 minutes and do not cut power to the system while it's blinking unless an extremely long time has passed like an hour.

*RAM is only supported to 2667 without overclocking, while it may run higher and a cleared BIOS will definitely work, automatic settings may not work for faster speeds depending on your RAM used.

 

[madsenmm]

So an update on this.
Apparently both the Motherboard, the CPU cooling and the PSU itself got fried…

not sure how the PSU itself decided to stop working.

I had done the paper clip test previously when the Motherboard started acting weird, and everything was good then.

So I got a new PSU and new CPU as I thought I maybe had killed that as well, and everything is running now, just need to change the CPU cooling as well now.

quite a surprise that mixed PSU cables, can kill the Motherboard, CPU Cooling and PSU itself at once. Lesson learned.