RESOLVED: PC fault diagnosis

TeaLeaf · January 05, 2021, 01:19:25 PM

Hi folks. Dex had a whining fan on his PSU which we decided to swap out for a brand new Corsair RM850. All cables replaced at same time with Corsair's.
PC worked fine with original PSU, it just a noise, but we went with a PSU swap as it might fail RealSoonNow. The new PSU replaced a very old (circa 9-10 years) Antec 1000W PSU. PSU requirement calculated at circa 510W, so a Gold 850W should be fine.
Also threw in a new 3TB HDD on a new SATA cable.
It had a ton of dust in it, this was hoovered out gently whilst carefully earthed.

After changes:

Booted PC and it had no picture on monitor (not signal). Started digging a bit.
Swapped gfx card for older card that I knew was working, no change. So it seems it is not a gfx problem.
Reseated RAM. No change.
Reconnected cables. Reseated.
Disconnected all drives bar the boot SSD. No change.
Booted without RAM sticks, no help.
No post beep.
All case fans spinning happily, apart from two case fans plugged directly into mobo which are not spinning. Tried booting without the fans plugged in, no change. Not sure if these were working or not before the PSU swap.
CPU cooler fan is still spinning (plugged into mobo) on power up. Mobo power light is on.
Noticed Gfx card fans on original card would momentarily start spinning and immediately stop. Replacement card we tried spun up the fan no problem at all. Both used the same 2 x 6+2 PSU cables.
Tried alternative DVI (yeah that's old) sockets on both gfx cards, no change.

So what took a working but whining PC and killed it? Any suggestions chaps? I'm currently at the "screw it, we need a new CPU/Mobo/RAM bundle" stage and want to avoid the cost (although Dex says the extra fps from new hardware would be nice!)

Any helpful suggestions gratefully accepted - may involve extra beers at the next available dMw LAN. :thumbsup:

Chaosphere · January 05, 2021, 01:35:49 PM

Does it stay powered on with no video out, or just immediately shut off? If its the latter it could easily just be a short circuit somewhere. The former needs a bit more digging...

I'd go back to basics.

Take everything out of the case.
Clear CMOS - remove the BIOS battery, disconnect all power.
Put the motherboard (with CPU and cooler) on a cardboard box.
Put in a single stick of RAM.
Connect a monitor to the motherboards video out.
Connect the PSU to the motherboard.
Turn it on - you do not need any sort of drive to get into BIOS, so don't plug these in.

If you get past POST and into BIOS then your CPU, motherboard, and that stick of RAM are fine.
If it doesn't work, try another stick of RAM.
If it still doesn't work, you can buy that bundle! :roflmao:

You can then add bits in one by one to find out where the problem lies. The bit you connect that stops it working is the broken bit :norty:.

smilodon · January 05, 2021, 03:22:39 PM

Can't give you the same level of advice as the Chaos-meister but I killed a mobo while swapping out a Graphic card.

Seems the mobo was on the way out, probably a cracked solder joint that was still making contact, and the flexing etc it got from pulling out the GPU and fitting a new one was enough to end it.

You're symptoms match mine quite closely.

sulky_uk · January 05, 2021, 04:56:51 PM

Again cant give Dr pc's level of advice but,

Funny thing, Paddy had exactly the same issues with his computer that has now been sent back to scan, waiting on a resolution, but I did the same as Ben directed.

Be aware though that some GFX cards have a zero fan setting, they whirl up on switch on, read the temp and then set the fans RPM to the number dictated in the fan curve, some default to zero if under 30c, it could be that you just noticed it as you had your head in the box, Could be the reason for that, could try it in another comp to confirm.

As for paddys comp, i informed scan that i thought it was a suspect modo as everything worked, but no display, although once in every 10 boots it displayed hit f2 or del, but hung there. did the same with multiple gfx cards

so pretty similar at the same time...spooky

Benny · January 05, 2021, 06:46:08 PM

To add my no value here. Took me fking ages to get the kids new pc working to a screen because it had defaulted to the onboard gfx. Then I didn't realise (odd) that the monitor had to be connected and on during the first boot to turn the output on.

Does caps work when it's powered up?

I shall now retreat to the shadows.

Sneakytiger · January 05, 2021, 07:30:59 PM

are you using the corsair 24 pin connector TL or the 1 from the previous psu?

sulky_uk · January 05, 2021, 09:05:15 PM

Quote from: Sneakytiger;444336are you using the corsair 24 pin connector TL or the 1 from the previous psu?

TL used the new PSU cables as per 1st and 2nd line

TeaLeaf · January 05, 2021, 09:42:54 PM

Thanks for the suggestions, I'll be giving the ones not already tried a go tomorrow. I'll report back!

Mikep1212 · January 06, 2021, 12:29:35 AM

So forgive me if I am missing something but did you try putting the old PSU back in the circuit?

The PSU appears to be starting as the case fans are spinning. If your 24pin is 20+4 Make sure the 4 is on the correct side. Make sure you haven't mixed up PCI-E with PERIF and CPU power connectors if all 8 pins from the corsair CPU. Seen this done before with modular PSU users.

TeaLeaf · January 06, 2021, 08:17:25 AM

Thanks Mike, I haven't yet tried putting the old PSU back into the loop, it's a good idea just a hell of a lot of time to do it, so I'll need to psych myself up a bit first.

24 pin on the Corsair is a single block, so no chance of it being the wrong way around. The cables are all clearly identified too, with CPU and PCI-E stamped down the side on those cables, so I'm confident that these are plugged in to the right places. CPU into the mobo, 2 x PCI-E into the gfx card.

Now to see if I can gather sufficient motivation to swap a PSU out for an older one, only to then probably have to swap it back out again........ :frusty:

Mikep1212 · January 06, 2021, 10:40:40 AM

Great, glad they're labelled. Both are obviously just 12V but the pinouts are different I have seen them mixed up in the past.

The only other thing is check the pins in the plugs haven't opened up and are now not making connection. Saw that on a Corsair thread last night.

Source: https://forum.corsair.com/v3/showthread.php?t=189694

TeaLeaf · January 06, 2021, 11:00:37 AM

Thanks, I'll check that too.

Gorion · January 08, 2021, 06:47:51 PM

Swing the tower slightly in case you dropped a screw in there.
Also try to reseat the CPU. During POST you will get error code beeps if the gpu or ram are faulty. But you don't get any if its the mobo or the cpu since the CPU is what technically starts the POST process, and it needs a working mobo and psu to work.

TeaLeaf · January 22, 2021, 11:07:16 AM

Reporting back on the fault resolution!

It turned out that a moving around of modular cables (at the PSU end) fixed the problem. The PSU comes with no manual and I could not find one online which clearly described what plugs into where. This has never been a problem before as all of the sockets are labelled, and many of the plugs only fit certain sockets. However, in this instance, the PSU does not label each individual female socket, instead it labels a group of sockets with a couple of different cable options (e.g. these sockets power 6+2PCIe and CPU4+4). There is nothing to say if e.g. cable option (A) fits into a specific socket from the group, or (B) fits into another one. Anyway, I moved one cable from the upper tier to the lower tier (with the same named options) and this seemed to fix the problem, all the fans spun up, the monitor lit up with a boot logo and the PC booted up without problem.

This is the first time I have ever had a 'wrong cable in wrong socket' scenario. Yes it might be a senior moment, but I have built enough PCs that I reckon I know my way around how to plug things in, so I blame seriously poor labelling and in-box guidance from Corsair. If they insist on labelling vaguely then they really should provide a labelled diagram to clarify things.

Take a look at the below picture and see if you can decide which sockets are for CPU4+4 and which ones are for PCIe6+2. Clearly it *does* make a difference which socket was used, so they are obviously *not* groups of sockets, so *why* label them as such! :frusty: Anyway, Dex has a working PC and is a happy bunny, so all's well that ends well.

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Chaosphere · January 22, 2021, 11:48:03 AM

Quote from: Mikep1212;444339So forgive me if I am missing something but did you try putting the old PSU back in the circuit?

The PSU appears to be starting as the case fans are spinning. If your 24pin is 20+4 Make sure the 4 is on the correct side. Make sure you haven't mixed up PCI-E with PERIF and CPU power connectors if all 8 pins from the corsair CPU. Seen this done before with modular PSU users.

Nailed it!

Glad you got it sorted, and glad it was an easy fix in the end!

The right answer to troubleshoot these things is often to just unplug everything and start again, its amazing how often this will lead to an easy fix!