Is my PSU broken?

milko

milko

milko

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That seems to me a strange question, I would've thought it should be obvious. But!

My PC was running fine two nights ago. I shut it down and went to bed. The next evening, when turning it back on, nothing happened. I have a power button built into the motherboard itself, and pressing that also causes nothing to happen.
What makes me have some doubt is that the power button and some other motherboard lights are lit up. As is the power LED on my external USB-connected card reader. So clearly some power is getting through.

Before I go spending most of £100 on a new PSU, can anyone suggest anything else I should be checking? Thanks!
 
You seemed have similar issue from other thread, guy fixed it by removed 2 memory sticks then reseated 1 stick, switched on PSU and powered on PC fine. He repeated the procedure removed 1 stick and installed other stick, switched on PSU and pressed power but PC wont powered on so guy RMA dead memory stick.

How many memory sticks you have?
 
I've got two memory sticks. I'll give that a try then, thanks for the tip. I wonder why such a failure wouldn't make the motherboard do POST beeps instead of just sitting there in silence.
 
Does your case have a speaker? I've found that quite a few cases don't have one anymore. It could just be trying to beep with a blank screen, but without a speaker.
 
Thanks all who've posted here. I'm gonna try that tonight, and the memory. And I've got a multimeter so I could maybe do something a bit more precise to test that PSU. AND I've checked out my motherboard manual (ASUS Maximus Formula VI) and there should be some error lights and/or numeric codes visible on the motherboard for a lot of POST-related stuff.

I'll report back with how I get on.
 
Here we go:

Ok. Paperclip and multimeter on the go. It seems to only be giving 3.3V out of the 12V line. That's broke then is it? Only thing that makes me doubt it is that maybe it has some clever "keep volts low if there is no load" thing going on? It's quite a fancy PSU (BeQuiet P8 1200W that I got from a friend and had running for a couple of years now) so I wouldn't be that surprised. It's just the rather precise 3.3 that gives me that thought. The 5V line is still 5V.
I also tried pulling the RAM and the graphics card out, that didn't help. Still no life, and none of the board's diagnostic LEDs are coming up. Reset the CMOS too, no help.

The fan on the PSU spins but if I connect a case fan to it (which is a bit awkward as none of the cables are a direct match, normally run via the motherboard) it doesn't spin at all.
 
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Oh hello. Different cable (same type) into different socket on the PSU and it reads 12.5V. Hffffffff.

Yeah, ATX is showing 3/5/12 as it should. Well, 12.5. Maybe one duff HDD molex cable was enough to cause this, plugging the other into the same bit works as well for the case fan. Weird. Time to put it all back together.
 
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And still nothing. Close to "throw it all out of the window" stage now.

Rrrgh. So I started again thusly: PSU connected to nothing, ATX shorted with paperclip. Powers on, volts read as they should. Plugged in the 'other' motherboard power (that fires up the CPU I think) and powered up, volts read as they should. Plugged in PCIe for the graphics, volts all good. Plugged in AIO CPU cooler power, volts all good. Plugged in hard drives power, NOTHING. Hello. Went back a step, nothing. Mixed and matched a few steps, nothing. Went back to just PSU With ATX cable shorted, nothing.

*flings hands in the air*

*goes to bed*
 
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This morning, PSU with ATX cable shorted is back to normal. Then l left for work rather than try and go through all that **** again. I have no idea what's going on anymore.
 
milko said:
Plugged in hard drives power, NOTHING. Hello.
Click to expand...

So your PSU shuts down when you introduced the Hard drives?

Maybe there's a short in the drive/drives or the cable running to it/them.

Once a decent PSU sees a short it'll shut down and stay down despite removing the offending short for a certain length of time. It forms part of the safety mechanisms.

If there's a short in the hard drive you should be able to see it with your multimeter in ohms or continuity across the 12v pins if you can get to them. I've seen quita few SATA power connectors melted by a short across the 12v and ground pins. Some of those SATA connectors are really quite shockingly poorly manufactured.

So does the system start without the hard drive now that the PSU has had time to reset the short condition?
 
This evening I'll try again and see if I can get through to the point of connecting the HDD again. I was using a different cable for the power last night than what I'd had before, so if it is indeed that, whatever caused it to happen still is doing it. I've an SSD and a regular mechanical drive on that line so I'll also only try one at a time this time.
 
Update time!

Set the whole power chain up again. If I plug in everything but the motherboard, and short the ATX pins with a paperclip, it powers on. So, motherboard failing, right? Switched it off again to think about the next thing I can do. Except I just thought "oh yeah, recheck voltage" and went back to it and now it will NOT power on. Wtf? Argh! I really wish I had a spare PSU to try out here.

After leaving it a while then trying again it switches on and let's me read a good voltage. It really seems that connecting the motherboard is the step that jiggers it and puts the PSU into some kind of safety mode that shuts off the power for a bit.
 
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I thought it failed on the hard drives step? Oh well if they allow it to run when they are connected then I guess not them

Anyway you can forget about CPU 12v and GPU not being the problem as they start to draw power later in the power on stage. They might not be. We just don't know.

Do you even get a twitch out of the fans when you connect the motherboard up? If not then you must have a short somewhere as overcurrent would take a moment of two to kick in. A motherboard failure would allow your fans to run.

If it were mine I'd be getting my multimeter out and checking across the 12v to ground wires for low ohms or continuity and working from there. It could be the PSU still though. None of the tests you have done are conclusive. You'd need a PSU load tester (or suitable home made equivalent) to be sure the 12v rail is solid.
 
Yeah it seemed to fail at hard drives earlier, but since then it definitely can run those. At some point.
Not so much as a twitch when the m/b is connected, no. I've got a multimeter but struggling for the expertise to get more conclusive. I've a new PSU arriving for tomorrow, see how that gets on and if it doesn't cure it I guess I'll have to learn how to dig deeper!

Thanks for all the advice.
 
Absolutely nothing happening. I've got the motherboard out of the case, no ram no graphics, literally just the CPU and cooler (corsair h80i so it's using a few plugs to supposedly power that). The motherboard lights come on as so as I turn on the PSU, but I can't get it to go any further.

Is it possible for the CPU to cause this, or am I pretty much able to blame the motherboard at this point?
 
Just to confirm for posterity, it was indeed the motherboard at fault - a new board in and all is running hunky dory. Well, except for that Windows is really upset about the change and I've had a heck of a time getting things like the network connection back up and running. I've fixed most things but it's still not happy so I'm trying to upgrade to Windows 10 since it's out today.

Thanks to all who posted in this thread, it was very helpful.
 
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