PSU problem

Hopefully this is the correct forum to use for my query.

On Monday I added a further hard-drive to my home built (PCPro spec) PC. On putting everything back together I go to switch on and nothing. Just the slightest hint of a couple of fans moving momentarily but certainly no more than a few millimetres. Now as the PSU is only 3 years old it seems unlikely it has packed up already and has never previously been an issue. So what else might be the cause? Any thoughts anyone.

Does it still work if you take the new drive out?

If so it could be that the higher start-up surge with an extra drive is tripping the crowbar protection circuitry in the power supply.

Disconnect drives. Be sure to check if the PSU and CPU fans are turning on startup.

In reply to a post by billford:

Does it still work if you take the new drive out?

If so it could be that the higher start-up surge with an extra drive is tripping the crowbar protection circuitry in the power supply.

Bill - it makes no difference. I now have the sides off and nothing else plugged into the back so it is only the internal bits of kit that are drawing power and more importantly can see exactly what does or does not happen when I press the on switch. The CPU fan and several other fans make an attempt at starting but merely twitch the once. A small blue light by the side of the one switch flickers for the merest of time. So I am still perplexed.

Sod's law says that my son has just rang from Gran Canaria and wants a copy of something on one of the hard drives!

In reply to a post by camieabz:

Disconnect drives. Be sure to check if the PSU and CPU fans are turning on startup.

Disconnected all four drives - the previous 3 and the new one and it makes no difference at all. The CPU fan and several other fans in the tower have a momentary attempt at moving but do nothing other than twitch.

Have you checked all of the power connectors, particularly the main one to the m/b, to make sure they are fully plugged in? It sounds to me as if you might have disloged one of the connectors slightly.

In reply to a post by AEP:

Have you checked all of the power connectors, particularly the main one to the m/b, to make sure they are fully plugged in? It sounds to me as if you might have disloged one of the connectors slightly.

Thanks AEP, I did do a quick check last night but it was getting late so I think I will systematically go through and check all connections to the motherboard and also where two cables get connected to each other. It may be that I dislodged something somewhere along the line.

Hopefully that will do the trick as there hasn't been the slightest hint of a problem from the PSU - it is a Zalman ZM600-HP Heatpipe Cooled 600W Modular PSU purchased in April 2008 and from memory I built the PC in late May early June 2008 by the time I had all the necessary parts. It is not my main machine as I mainly use my iMac My son did use it for his course work and his business when he lived here.

I would test the PSU in isolation, to rule out the motherboard. Unplug all the cables including the two motherboard ones. Get the 20/24 pin main motherboard cable, bridge pins 13 and 14, 14 is what tells the PSU to switch on, 13 is just ground (you can use any black wire). It's an easy wire to spot as it is the only green one and it's right next to the clip. Pinout; http://pinouts.ru/Power/atxpower_pinout.shtml
Once you've bridged it, turn the PSU on and either the PSU fan will spin up or it won't. If it doesn't it's knackered, but even if it does, it could be that the PSU is putting out low voltage on one or more of its rails, but that is pretty rare tbh. Usually they just go completely in my experience. You'd need another PSU or a multimeter to go any further.

Edited by deleted (Wed 22-Jun-11 20:10:11)

I used to see some psu's behave like this after a dirty shutdown,
one trick was to unplug the whole machine overnight, and magically it worked in the morning.

Thanks - but the issue is now 3 days old so has been switched off since Sunday, which is when I started on this 'quick' task! No change since then. Looks like I may need to dig out my paper work to check the warranty period or buy a new PSU. Not sure whether it has 2,3 or 5 year warranty. Knowing my luck it will be 3 years and just outside! If it turns out not to be faulty but is a motherboard issue at least I would have a spare PSU. You have to look on the bright side somehow.

In reply to a post by 12eason:

I would test the PSU in isolation, to rule out the motherboard. Unplug all the cables including the two motherboard ones. Get the 20/24 pin main motherboard cable, bridge pins 13 and 14, 14 is what tells the PSU to switch on, 13 is just ground (you can use any black wire). It's an easy wire to spot as it is the only green one and it's right next to the clip. Pinout; http://pinouts.ru/Power/atxpower_pinout.shtml
Once you've bridged it, turn the PSU on and either the PSU fan will spin up or it won't. If it doesn't it's knackered, but even if it does, it could be that the PSU is putting out low voltage on one or more of its rails, but that is pretty rare tbh. Usually they just go completely in my experience. You'd need another PSU or a multimeter to go any further.

Thanks for this and for the helpful link.

So to make sure I understand correctly before carrying out this tricky task. I hate having to remember where all the various wires go. What I need to do is disconnect every wire from the PSU - presumably I can do that from detaching at the PSU cable end of things rather than removing all the small wires to the motherboard and 4 independent fans. Once achieved bridge pins 13 and 14 and turn on the PSU and see what happens?

Await confirmation before attempting. I should have just waited until I really needed the extra capacity on my hard-drives but I have had it sitting there for 12 months waiting for an opportune moment - clearly it wasn't last weekend!!!

I have also seen corrupted cmos values make a machine fail like this, ( for example, the processor thinks it should run at 14tHz... )
testing the psu in isolation( following 12easons advice) should help determine psu or elsewhere, but generally psu's should be tested with some load.

Another thing that can cause this sort of problem is a motherboard shorting to the chassis. The only real way to test that is to take the motherboard and PSU out of the case, put them on an insulated surface with the power connectors plugged in and see if it works (or at least the fans spin). But that's a pain and I can't see how just plugging a new drive in can have made that happen (but it could easily have led to a disloged cable).

Hopefully it will turn out to be something trivial. Good luck.

Good point. It may be worth clearing the CMOS by shorting the appropriate jumper.

reseat RAM, unplug HDD/optical disk drives, replug connections, remove power fully, remove stuff plugged into back of mobo, remove CMOS battery for 30 min. Put bios battery back only, try again.

In reply to a post by lenaspell:

So to make sure I understand correctly before carrying out this tricky task. I hate having to remember where all the various wires go. What I need to do is disconnect every wire from the PSU - presumably I can do that from detaching at the PSU cable end of things rather than removing all the small wires to the motherboard and 4 independent fans. Once achieved bridge pins 13 and 14 and turn on the PSU and see what happens?

If you have a modular PSU with detachable leads, then detaching them at the PSU would be a whole lot easier. You only need the main motherboard cable. Just make sure the 4pin processor cable is unplugged too, those usually aren't modular.

In reply to a post by 12eason:

In reply to a post by lenaspell:

So to make sure I understand correctly before carrying out this tricky task. I hate having to remember where all the various wires go. What I need to do is disconnect every wire from the PSU - presumably I can do that from detaching at the PSU cable end of things rather than removing all the small wires to the motherboard and 4 independent fans. Once achieved bridge pins 13 and 14 and turn on the PSU and see what happens?

If you have a modular PSU with detachable leads, then detaching them at the PSU would be a whole lot easier. You only need the main motherboard cable. Just make sure the 4pin processor cable is unplugged too, those usually aren't modular.

Excellent - yes the Zalman ZM600 is a modular PSU so that makes life much easier. Will have a quick cuppa and then got on with the task. Thanks to everyone else with ideas - I will work through them all to eliminate things. Even in large towers there never seems enough room to do things easily!

In reply to a post by Pipexer:

reseat RAM, unplug HDD/optical disk drives, replug connections, remove power fully, remove stuff plugged into back of mobo, remove CMOS battery for 30 min. Put bios battery back only, try again.

Thanks - I will give it a try later.

12eason - the PSU blue light glowed for a couple of seconds and the fan spun for the same length of time and then stopped. I tried it a couple of times and the same thing happened but it doesn't remain on so I guess it is in fact a fault on the PSU.

I have to say it is a lot easier removing the modular cables from the PSU

I now have the sides off and nothing else plugged into the back so it is only the internal bits of kit that are drawing power and more importantly can see exactly what does or does not happen when I press the on switch. The CPU fan and several other fans make an attempt at starting but merely twitch the once. A small blue light by the side of the one switch flickers for the merest of time. So I am still perplexe

Sounds like one of the PSU protection circuits is kicking in - you get a brief surge of power, then the PSU measures something out of spec (voltage, current, whatever) and turns itself off to protect itself and/or the motherboard.

EIther that or the motherboard power on circuitry is faulty.

Really need to check the PSU in isolation as others have suggested, or at least with the M/B out of the case and minimum hardware installed (CPU, some RAM and Video)

Thanks - please see my recent post in connection with the psu test in isolation. By grounding pins 13 and 14 I was able to get some life but only for a very short time though the internal blue light came on and the fan spun briefly. I repeated a few times with the same results. So I will speak with my supplier tomorrow but as the latest Zalman's only come with a 3 year warranty I fear I am just outside that time frame.

They timed that component failure well then didn't they.

Didn't they just. Now I don't know whether to go for another Zalman or change the make. I have been very pleased with it up to now and it is very silent along with the other very quiet fans. You wouldn't know that the PC is on unless you get very close. Certainly a huge improvement on all previous machines and a great feeling to know that I built it myself from scratch (albeit broadly following recommendations in a PCPro article) having never done anything like it before.

Post deleted by c_j

i been using Corsair power supplies for the last 18 months they seem to be reliable and a pretty good price.

I put four of them in different machines in the last 12 months. My own is around 18 months old and been taken out of my old machine.


Pretty quiet as well considering it is fan cooled. not sure if I like the idea of these power supplies that don't have fans

Well I had the Zalman tested and it is working fine with the internal light and fan operating as usual. But I also borrowed and fitted an alternative PSU and had the same result so it looks as if the fault is elsewhere. So I did a dis-service to Zalman suggesting that the product failed just out of warranty. Ooops

So back to square one and much gnashing of teeth while I try and figure things out.

Not sure I would want a totally fanless PSU either so am in agreement with zyborg.

I'm not sure that testing a PSU whilst not under load is terribly informative. I'd try just the PSU and motherboard out of case to eliminate short circuits. If that fails to run then it looks like it's the motherboard and/or processor. Unless you have a spare processor it might be difficult to determine which. Any dodgy looking (bulging) capacitors on the motherboard?

The good news is that it's probably almost as cheap to replace them as the PSU. Novatech do nice cheap motherboard bundles.

Good luck.

In reply to a post by AEP:

I'm not sure that testing a PSU whilst not under load is terribly informative.

It would not be informative if your goal was to measure the voltages, but seeing if it works or not is fine. All PSUs must power on if the green cable is shorted, it's in the ATX spec. They do not have some sort of load detection and auto shut-off feature.

seeing if it works or not is fine

Apparently not, in this case, according to the OP.

Could have been a internal fuse that needed a few hours to reset, could have been a bad short on the power wire.

Could have been. But it appears that the OP is still having problems.

In reply to a post by 12eason:

In reply to a post by AEP:

I'm not sure that testing a PSU whilst not under load is terribly informative.

It would not be informative if your goal was to measure the voltages, but seeing if it works or not is fine. All PSUs must power on if the green cable is shorted, it's in the ATX spec. They do not have some sort of load detection and auto shut-off feature.

The issue really does point to the motherboard, other component or loose connection somewhere. However I have checked, double checked, removed and then placed back all cables. I have tried out a brand new PSU on the system with all internal connections fitted and I get the same result as with the original PSU - so that seems to eliminate the PSUs in my admittedly non-techy opinion. The fact that the previous PSU, which I did think was the original culprit does in fact power up (under test conditions with no load admittedly) does suggest the fault is elsewhere.

I have checked the power on switch on the top of the tower has not had its wires detached. Given that I hadn't had the slightest problem with the system prior to fitting the new hard drive is the perplexing part.

I have tried to power up with no hard drives connected as well as with just the original three rather than the four now installed. None of which has made any difference. I am just about to try a new cmos battery as suggested by another response. So back to the drawing board

The new PSU presently borrowed and in the machine is an impressive beast - a Nesteq ASM x-Zero 700W - http://www.nesteq.net/gb/products/powersupplies/asm_...

When the power cord is fitted and the switch turned on only the one green light comes on for the 5Vsb not the other three lights.

I don't think you'd need a new battery, just reset the cmos. The worst that will happen if the battery has died is that the computer won't be able to keep time. You'll have to refer the the manual for the motherboard for the correct pins to short to reset the cmos. It's usually a three pin set near to the battery. Obviously, you can remove and reseat the battery too.

Hope it is the cmos, because all the other options are rather more serious. Neither faulty ram or a faulty processor will stop the motherboard powering up and the fans spinning, iirc. So it'd probably be a duff motherboard.

Edited by deleted (Sat 25-Jun-11 17:51:28)

In reply to a post by 12eason:

I don't think you'd need a new battery, just reset the cmos. The worst that will happen if the battery has died is that the computer won't be able to keep time.

Interestingly, I've just had a battle with a non-booting PC. Lights come on, fans rotate, HDD rotates, CD drive rotates, but nothing shown on screen and no POST beeps.
The mobo is ASUS.
I couldn't make any progress until I decided, in desperation, to replace the CMOS battery - when everything burst into life once more.

I was willing to swear it couldn't give the particular symptoms as a result of battery failing, too !!

Edited by dandnsmith (Sun 26-Jun-11 09:44:28)

Does sound odd. I'd have thought the cmos battery was solely used to maintain a clock nowadays. Just assumed all other data was written to flash type memory.

eta: http://en.wikipedia.org/wiki/Nonvolatile_BIOS_memory

Edited by deleted (Sun 26-Jun-11 10:31:52)

In reply to a post by 12eason:

I don't think you'd need a new battery, just reset the cmos. The worst that will happen if the battery has died is that the computer won't be able to keep time. You'll have to refer the the manual for the motherboard for the correct pins to short to reset the cmos. It's usually a three pin set near to the battery. Obviously, you can remove and reseat the battery too.

Hope it is the cmos, because all the other options are rather more serious. Neither faulty ram or a faulty processor will stop the motherboard powering up and the fans spinning, iirc. So it'd probably be a duff motherboard.

Well new battery fitted so apart from resetting the CMOS I have achieved nothing. I am only left with the likelihood of a motherboard that for whatever reason has died on me and the fitting of a new hard-drive was merely coincidental. Goodness knows why the mobo has failed though.

Now need to research a suitable replacement. Oh the joys of computing...... of course SWMBO is not impressed at a week lost when I should be doing other things let alone the cost of it all

I am only left with the likelihood of a motherboard that for whatever reason has died on me and the fitting of a new hard-drive was merely coincidental.

Have you eliminated the short-circuit possibility by trying the motherboard out of the case? It's a very common cause of the sort of problem you describe. You could easily have moved something when you installed the drive. (Or even dropped a screw into the works - it happens!)

If you're thinking in terms of replacing the motherboard then you're going to have to take it out of the case anyway. You might as well try testing it then, even if it's a remote possibility.

In reply to a post by AEP:

I am only left with the likelihood of a motherboard that for whatever reason has died on me and the fitting of a new hard-drive was merely coincidental.

Have you eliminated the short-circuit possibility by trying the motherboard out of the case? It's a very common cause of the sort of problem you describe. You could easily have moved something when you installed the drive. (Or even dropped a screw into the works - it happens!)

If you're thinking in terms of replacing the motherboard then you're going to have to take it out of the case anyway. You might as well try testing it then, even if it's a remote possibility.

Good point - no harm in giving it a try at least. Think it will have to wait until I have done a few outdoor jobs first particularly since it is such a pleasant day and I don't have another mobo to replace anyway. I will let you know if it springs to life. Ever hopeful

This is gonna be mother board and not PSU.

I would take everything off that board and fit one piece at a time and try boot after each one ( including on a empty board) see if it powers up at any time..if not its the mobo

Just to close off this thread. It was indeed the motherboard so have taken the opportunity, after much thought and angst, to upgrade both board and processor.

Thanks to everyone who helped trace the fault eventually.