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System suddenly not powering on

Last response: in Systems
April 7, 2012 5:09:37 PM


I build a system based on an Asus x58 Deluxe v2 board several years ago, and its been running perfectly fine since then (though around a year ago I replaced the RAM and the power supply). For the last few days it was sluggish (e.g. when locking the computer the "lock" sound would drag on for a long time, and when unlocking it, it would lose all responsiveness for 30secs). This morning though it would not turn on. The power supply fans never started, there were no beeps, no sign at all that I'd pressed the power button. Pressing the on motherboard power button produced exactly the same results (i.e. nothing).

My immediate assumption was that the power supply had died (though there were some lights on the motherboard still). I ran a power supply tester tool I had though, and this produced no warnings (all voltages were fine, the power supply fan did start which it did not do after pressing the PCs power button).

It can't be any software problems, and I haven't updated the bios or anything recently. Indeed, since the power supply button isn't even starting the power supply, I think that means it couldn't even be a bios problem, as it's not getting as far as loading the bios.

Am I right in assuming that I'm going to need a new motherboard and/or CPU? There are some obvious other tests it would have been nice to perform (removing cmos battery, resetting bios etc.), but I'm now on holiday (I only just had time to test the power supply before leaving), and ideally I'd like to order whatever I need so that it arrives before I return, if I'm at least 95% confident that I've identified the problem.

Any thoughts or opinions would be much appreciated.

a c 78 B Homebuilt system
a b ) Power supply
April 8, 2012 3:19:19 AM

The voltage meter you used can't tell you what you need to know about this PSU, most likely.

Most voltage meters are not designed to provide good information about switching mode power supplies, which PSUs are. Switching mode PSUs can detect problems in their own voltage and correct them in a matter of milliseconds. That is faster than these devices can detect there is a problem.

The thing that matters most for being able to turn the computer on is one single wire called +5vsb. This is the only wire that has power running through it every minute of the day as long as the PSU is plugged into the wall.

Coincidentally, this wire is also why people should never work with their internals while the power cord is plugged in, because this line still transmits power as long as it is plugged in.

The +5vsb line has very little power capability, obviously it is a 5v line, but it has very little amps which multiplies out to very little wattage.

It might have, for example, 3a x 5v = 15w. That is not a whole lot of juice, even if the PSU is brand new.

As PSUs get old, they lose capacity on all their lines over time, and because this line is generally so small to start with, it is usually one of the first to demonstrate a problem in regular usage.

All the problems you mentioned (indeed nearly all problems in a computer) can be due to a PSU and especially when computers are having problems waking it up that usually points directly at the PSU.

The only way to really test this is to try a different PSU.

However, it is worth noting that USB devices use power even when the computer is off. They suck juice like fiends through the +5vsb wire. The same one that computers use to turn on. If you have lots of USB things plugged in, they can divert power away from the power button and keep it from ever getting any power.

If you have lots of USB things plugged in, try unplugging all of them and hitting the power button again. That includes keyboards and mice too.

If you can turn the computer on with no USB devices attached and you can't turn it on with USB devices attached, that means bad PSU.

However, I feel like I need to have an aside here.

You are running through PSUs entirely too quickly if indeed this is a PSU problem as I suspect. That says to me that the computer as a whole isn't functioning well.

More to the point, it tells me that you need a new case.

If you would, please let me know the maker/model of your case so that I can confirm whether this is the case or not (no pun intended).
April 8, 2012 10:44:31 AM

Thanks for the comments.

The case is a Lian Li PC-A20A, with some fans swapped out for Yate Loon D14SL-12. Bought 24/03/2009 according to my Google logs. The PSU is in a separate section at the bottom with the hard disks.
The original PSU was a Zalman ZM-1000-HP. Apparently I bought it before the case on 29/08/2008. Must have used it in my old PC first. It was replaced with a Zalman ZM770-XT bought 01/09/2010.

Oh and the motherboard is an Asus P6T Deluxe v2. Are you sure it couldn't be something on the motherboard? The motherboard lighted power buttons were glowing suggesting it was getting some power through the five volt line.

I'll try your unplugging USB devices test when I get home in a week. Are you confident enough in your "its the PSU" diagnosis to recommend that I buy a new one now without having been able to try the "unplugging USB devices" test? Assume I value having a PC that works on day 1 of my return at about half the cost of a new PSU...

Thanks in advance,

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a c 78 B Homebuilt system
a b ) Power supply
April 8, 2012 10:53:20 PM

I am not entirely sure that it is a problem with the PSU and yes it could be the motherboard, but my gut feeling at this point is still PSU.

I did some research into Zalman PSUs and they really like to toe the lines about what is and is not acceptable voltage limits. In the information I looked at, if 60% or more of the maximum wattage was pulled from the PSUs, they would start running too far outside of specifications.

Running outside specifications can damage parts. Even running at specifications can, but definitely running outside of them can.

It is possible that some of your other hardware was damaged if these PSUs were being run outside spec constantly and for long periods of time.

That would lend weight to your other parts being damaged theory.

As for the 5v line still giving some power. That is normal, as long as power hits the motherboard out of the 5v the thing will light up. Where it gets redirected to after that depends on the path of least resistance.

There could be more juice being pulled than the maximum the line can deliver, and it could be essentially random which devices end up getting power and which ones not. Often the USB devices do win, though, for whatever reason.

How many USB things would you say are plugged into the computer right now, as an estimate?
April 8, 2012 11:28:32 PM

A few, but most of them have independent power sources. (DVD drive, two USB hubs in monitors, card readers, wireless mouse transmitter, keyboard, printer, possibly a webcam, hard-disk, and/or wacom tablet though I think they're all unplugged at present). I remember the DVD drive was whirring when I disconnected the mains power from the PSU, though it did have an independent power supply. The only other thing that might have been drawing power plausibly is the wireless mouse transmitter, but that was plugged into the monitor hub, and so should have been drawing power from the monitor if anywhere.

I don't think I can have gone over wattage. 1000w is a ridiculous amount even with my old 4870x2. I now have a single GPU nvidia card which draws a lot less, and in any case I haven't played any games since Christmas. The CPU may have been used quite heavily for work simulations, but that shouldn't have ever pushed me anywhere close to the listed wattage.

I was thinking about other possible causes for this, and I do remember that earlier in the week my amplifier turned itself off randomly, and wouldn't switch back on immediately. That could be evidence of a surge I guess, which in turn could have damaged something in the PC. I really ought to have a surge protector...

The timing was really terrible. If it'd happened one day earlier I could have run some of these checks before I went away...

Anyway, thanks for all your help so far.
a c 78 B Homebuilt system
a b ) Power supply
April 9, 2012 12:38:41 AM

If indeed it was a power surge then any of a lot of things could have been fried including the PSU.

Interestingly, the surge protectors just trade one problem for another one pretty often.

They usually (afaik) shut themselves off completely and allow no power to flow through the device when it detects a power surge.

So instead of getting a catastrophic surge of power they get a catastrophic loss of power.

Thankfully, a complete loss of power is usually better for computer components than exposing them to way too much power.

One thing you can do to help mitigate that is to get an UPS and plug that into the wall, then plug the surge protector into that, and plug your stuff into the surge protector.

A lot of UPS have anti surge stuff in them, in which case they will switch over to battery power so the surge protector can still pull juice out of it and everything can keep going. If the surge made it through the UPS it would be no different as to whether the UPS weren't there.

You also get protection against power outages with an UPS too, which is the main benefit. That keeps you from having catastrophic power loss in those cases.

Anyway, if indeed you had a power surge and your computer was exposed to it, then the PSU is almost definitely fried. Maybe something else in addition.

I would really like to see you going again on day 1 when you get back, but I also don't want to see you waste money either. At this point I am not 100% sure a power surge occurred, though it would make sense with the symptoms.

However, even if you got a new PSU, the power may have traveled down through the PSU wires to the motherboard, hard drive, or god knows what and just replacing the PSU may not get you going again.

At this point, I can't fault you for getting a different PSU, but there is just too much up in the air at the moment for me to get completely behind that course of action.
April 9, 2012 8:41:01 AM

Replacing a PSU is certainly going to be less hassle less money than replacing the motherboard, so I'm going to hope for the best and order a new one (along with a UPS/surge-protector). Fingers crossed.

Thanks for all your help.
a c 78 B Homebuilt system
a b ) Power supply
April 9, 2012 2:10:03 PM

Make sure you are getting one of the really good brands of PSUs, they last a lot longer usually, and they don't go out of spec in their power delivery above 60% load.

I would get something from Enermax, they are the best brand at 1000w and up.