Power failure, but not complete

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My desktop (a home built machine) just clicked and went dead a few minutes ago.

The PSU is a Corsair HX850,  which (checking my old expenses) I see was purchased 8.5 years ago. It hasn’t given me any trouble until now. Almost all the components are RGB.

I disconnected from the mains, switched the PSU off, and let it cool down for half an hour, then plugged it back in and switched the PSU on. The LED panel on the motherboard was illuminated, the keyboard lit up, and a controller connected to a USB socket  buzzed. So there’s at least some power getting through. When I press the power switch on the front of the case the memory strips light up, but nothing else happens; no fans, no disk action, the DVD drive won’t open.

Before I rush out and acquire a new power supply, is it possible that the PSU is OK and the problem is the motherboard? Or something else?

Cheers
T

 

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Check the voltage on the power good line (usually a grey wire) – it should be 5V if the supply is working.

That being the case, if your confident you can sort out the settings, try a CMOS reset as that data can get corrupt if the system crashes (I’ve seen it a few times with CPU overheating..)

Next, make sure you have some sort of speaker on the main board (it can be soldered in, just needing a jumper left in the default place..). If the CPU is active the machine should bleep if started with the memory removed..

The lack of DVD activity is perhaps a bit of a red herring – it could be lack of 12V supply, which would imply a CPU regulator fault (but could it be an IDE drive with the data bus locked out? as said, never seen that one.) With a regulator fault, unplugging the ATX2 (4/8 pin with yellow and black wires) should get the tray working but I both haven’t had a PSU work under those conditions, and if yours does it leaves you with potentially replacing PSU, motherboard and CPU, all the CPU regulator faults bar burned connectors I found (admittedly only three, and two were spillage)  have killed the CPU eventually.

Finally you say the keyboard lit up – background illumination only? (in which case it could be just standby power, (5V, usually purple or mauve wire) but not stable enough to operate which causes the grey wire to remain below 2.5V holding the machine in reset to prevent clock drive and minimise damage to the silicon)

If the keyboard lights flash and go off it looks like a later Post fail in which case rearranging the memory might get things moving. Final note – power on is usually green (sometimes grey but that’s more often -5V) – below 2.5V turns the main power on, all black wires are ground. Orange is 3V3 for chipset and the like.

To be honest the PSU is the cheapest bit unless you plan to buy for upgrade so probably just try another. Maybe you can borrow one locally for testing?

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aquatarkus

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When I say the keyboard lit up, I mean that the backlighting of the keys (RGB) is on. The keys themselves do not seem to be doing anything – pressing caps lock does not illuminate the caps indicator for example. But if I plug the controller into the USB slot on the keyboard it still buzzes when I turn the PSU on.

Oh, with the PSU switched on the front power switch on the case is not illuminated, but if I press that switch the memory LEDs light up and the case power switch comes on. Nothing else though.

I can get hold of a replacement PSU relatively easily; what’s the likelihood that my other components are fried, d’you think? (Not asking for any guarantees, just wondering where I should set my expectations and how depressed I should be.)

cheers
T

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To start somewhere you’ll need the PSU replaced as if that’s not doing its job nothing’s going to work properly. I’d start with that as a first action and disconnect absolutely everything else from the power and motherboard connections (so you literally have a powered motherboard on  working PSU, CPU and memory only in the board, and turn the main power on by bridging the power switch connections with a screwdriver. If you have no speaker to hear a bleep you’ll have to keep the keyboard to try the caps lock test if you had a separate graphics card.

The reason for the screwdriver turn on is a stuck or “leaky” switch can cause problems – sorry, I forgot to suggest unplugging the reset switch during diagnostics – most newer OEM machines don’t have a reset switch. If you have a faulty reset switch it can replicate the effect of the PSU not asserting the power good, though it won’t affect that voltage reading.

If that doesn’t work then try the CMOS clear jumper again (power off and drain the power by trying to turn it on before moving the jumper.. and leave it a minute) then REMOVE the battery before moving the jumper back and trying again – it won’t hold settings but that makes sure the code BIOS detects a battery fail and defaults if it’s trying..

Then if still no joy, reseat the CPU (the PGA chips were worse than the LGA for poor connections but heat and fine dust is a large factor in the reliability with either), juggle the memory modules and see if there’s any life. If all that fails to produce any sort of activity and your display port is on the motherboard then I’d be looking to swap the plugged items as the motherboard is likely to be the harder and more expensive part to find. If you have a graphics card which plugs in, perhaps start there, especially if you find the fan cooling it has given up (that’s easy to miss) but if it is the cause removing it should increase the signs of life in the “memory out” test.

If you could perhaps post the motherboard model (or the machine model for OEM) someone might have posted a similar problem / solution to inform the likelihoods for the cause..

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aquatarkus

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Hi

The MB is a ROG STRIX Z390-F and the CPU is i9-9900K. GPU is GeForce RTX 2060 SUPER XC. The C drive is a 512GB SSD and there are three other HDD (although one is just the C drive from this machine’s previous incarnation).

If that helps

cheers
T

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Eight years and six months is a good life span for a PSU, but all of them fail in different ways.

Weird question but it is important, have you smelled any odor?

Burning or burnt power supply parts, and capacitors (large and small round cans) can emit acrid smells and sometimes (magic) smoke. Also look at the power supply’s circuit board with a bright flashlight for visible damage.

If failed capacitors do not emit an odor the can also silently leak their corrosive electrolyte causing damage from the bottom; Or they vent gas through the top and you will see the exposed metal forcefully opened similar to a canned drink causing a slow drying out over time. Any of these signs are good cause to replace your power supply.

The sound of an attached controller buzzing is a unwelcome sign… Do not despair yet, replace the power supply and test, hopefully the current one has not been frying your motherboard.

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If the keyboard lights up normally when you power the machine up, then the machine is powered up but doesn’t run.

Unfortunately, it could be either PSU or mobo and there is no easy way to test this without the right equipment.

cheers, Paul

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No odor, at least not that I noticed. There has been a little more noise at times since the beginning of the year, and there are quite a lot of tiny white flakes collected around the base of the PSU housing (see attached).

 

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Given the age and the power consumption of the machine I would expect that PSU to last it’s MTBF and probably not much more. You could possibly enumerate it’s running hours by reading the running hours from the original C drive which presumably stayed in the machine running while the PC is on (crystaldiskinfo) and comparing it to the datasheet value (100K hours which would show as 186A0 in raw data, figure from https://www.corsair.com/uk/en/Categories/Products/Power-Supply-Units/hxi-series-2017-config/p/CP-9020138-UK#tab-tech-specs)

As suggested by https://www.askwoody.com/forums/topic/power-failure-but-not-complete/#post-2434992 if you see capacitors which look like the ones shown by https://www.google.co.uk/search?q=failed+capacitor+split+vent&source=lnms&tbm=isch in your PSU then there are probably issues.

That said the product page now indicates a 10 year warranty so maybe you could “negotiate” an advance replacement – they can probably tell from the serial when it was made so maybe don’t open it up to look just yet, just look through the fan..

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Update: I had already ordered a new PSU from the supplier accompanied with a dialogue about exploring the warranty option. They kinda brushed that aside, but the new PSU (the same HX850 but with a 10 year warranty now) arrived today and when I swapped it for the old PSU (I had to do a bit more cabling work than expected because the connectors have changed slightly) everything worked perfectly. I’m not going to cry over $200 when I was half-expecting a considerably bigger bill and days more inconvenience.

All’s well that ends well, I guess.

Thanks everyone for your assistance.

cheers
T

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Lars220

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