PSU Testing Basics for Techs
The computer just won’t boot up. Yes, the cord is plugged in, the PSU switch is on, and the red voltage switch on the back is set to the correct voltage. You’ve eliminated the possibility that the power switch on the machine failed as well. Now what? In this article we’ll walk through some basic troubleshooting steps when testing a PSU for failure. If at any point you determine that the issue is not the PSU, I’ve included a link to a handy flowchart for PSU Testing at the bottom that lays out some more complex steps involved that can help you narrow down the problem.
1. Before you get started testing any PSU, you should find out from the owner of the machine what led to this inoperable state. Is this a new build? If it has been in use for some time, was there an electrical surge? A lightning storm? Electrical work done on the house? Was new hardware or software installed recently? Were any objects inserted the wrong way into the machine ports such as USB drives or media cards, inserted into the wrong ports altogether, or were foreign objects involved? Was there any smoke when the machine failed to operate, or any burning smell? These are important indicators that can save a lot of troubleshooting time.
2. If there were noises or smells reported by the client, I wouldn’t recommend trying to power up the machine with it in. It’s not worth damaging the machine over the cost of a new PSU. It would be better to use a PSU tester on it first, if you feel inclined to believe that the noises and smells were possibly coming from another source. If there were no noises or smells reported by the client, try booting the machine. Observe the PSU when attempting to power up the machine, and note any noises or smells coming from the unit. If you get odd noises such as sparking or bad electrical smoke smells, unplug it immediately, and replace the power supply with a unit matching the specifications of the original unit.
3. If the fan spins or the hard drive spins when you attempt to power the machine on, the problem may lie elsewhere. You might want to check for any of the ‘beeps’ that indicate issues such as memory problems or other issues. If the fan doesn’t spin, and there is no change in the state of the machine, continue troubleshooting.
3. Check all the PSU connectors in the machine. If any are loose, that could be an indicator of a problem other than the actual PSU components. You may want to disconnect all connectors and reconnect them to eliminate any doubt as to that possibility.
4. Many motherboards have a small LED, and if this is on when you have the PSU plugged in, the PSU is sending power to the board. If it’s off, you will need to continue troubleshooting. If it’s on, you may try disconnecting all the hardware connectors to the motherboard to determine if hardware may be causing a short in the machine. Sometimes media card readers can cause issues where a short will cause the PSU to behave as if it was failing. If you still can’t locate the issue, continue troubleshooting.
5. Use a PSU tester. Yes, you can use a voltmeter, but PSU testers are cheap, and they’ll save you a lot of time. You can also test a PSU by shorting out two of the pins, and while it seems like an easy check, it won’t tell you everything, and a PSU tester will also work towards demonstrating to the client that you have the tools for the job and don’t need to ask for paperclips to get it done. This step can often be done first to eliminate the possibility of a failed PSU, but if the PSU still fails to power the machine, you’re still at square one on troubleshooting.
6. If you have a spare PSU that meets the wattage and electrical specs of the original PSU, swap it out, and see if the machine boots. If you’re certain your PSU is operating correctly, and the machine still fails to boot up, this is an instant sign that something else is the problem, and you’ll need to continue troubleshooting other electrical problems or hardware problems.
Depending on the results you get from the tester, you may realize the PSU is bad and it needs to be replaced. Check to see if the PSU is under warranty, and if it is, contact the necessary party and arrange for replacement. If the PSU is under warranty, you should be aware that opening it may void the warranty, so resist the temptation to check out the inside of the PSU before checking for a warranty. You’ll also want to beware of electrical shock, as some components inside the PSU may store an electrical charge even after having been disconnected.
When replacing a PSU, make sure you ensure it provides enough wattage for the machine, and that the specs match the original PSU. Failing to do so will damage the machine. Also, be sure to have the PSU switched off when working inside the machine. A dropped screw or other metal object could land in just the wrong place, causing a short and potentially damaging the motherboard.
If you’ve determined that the power supply is not the problem, you’ll want to do some more troubleshooting along the lines of this chart here, which goes into expanded troubleshooting beyond PSU testing in much more detail and in an easy flowchart method.
If you have an odd or interesting story regarding PSU testing, drop a comment below!
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One comment, some of those cheap PSU testers use a LED to indicate if there is a problem with a voltage, they can lie to you! It can be bad, and the LED will light up. Typicaly you will find one of the Electrolytic condensers inside the PSU with a domed top or pushed over at a angle. The Condenser should be flat on top not slightly domed.
Use another PSU, or I rigged up an tester using auto lamps. They draw a lot more current from the PSU, and it is a better indicator of sufficient current to operate the Computer.
A LED just does not draw enough Current to be truthful, and you may be purchasing a PSU you do not need to. A spare PSU is a better way to go than those cheap PSU testers.
Old E.T.
I’m sorry but there is just a lot of bad information in this article.
A PSU tester does nothing other then show you that some “range” of voltages are being sent through the lines under no load and that it isn’t completely burned up.
For instance, just because the 5V LED is lit up does not mean that your getting the correct voltages. It could be lower (or even higher) and the LED will still light up. The LED is lit, but the voltage level could still be causing a problem. Most importantly is that these testers do not test the power supply under a load, which is all but worthless when troubleshooting problematic power supplies.
Shorting out the power on wire and a ground wire and then testing each voltage with a good voltage meter will tell you only slightly more, you will be able to verify that the voltages are within tolerance levels under no load.
The best way to test these would be to smell them for electrial burning odor, inspect the inside for burning or swelled caps and swap out for a known good working power supply. Swapping out for a new power supply is probably the fastest and best way to know for sure that the power supply isn’t the issue.
The voltage testers we use give us an exact -/+ voltage over each of the channels so it is quite accurate and it gives me the information I need in 2 seconds.
A good PSu tester is a bit more than those cheap ones but still less than $30.
I think the article is pretty fair in accuracy.
Our procedure is: Query the client during check in, as to when it worked last and what changed since then (as stated in the article); Inspect the computer motherboard for blown capacitors; check for burnt sights and smells, and then we hook up the power supply tester. If the PSU is bad we replace it if not then we look elsewhere such as switch, motherboard….
I know others have said it, but I will add my own experience as well. A PSU tester is a great tool to have, but can be inaccurate. They are great for quickly finding dead PSU’s, but 100% rule out a problem. You’ll have false positives, but never false negatives. There is no substitute for an experienced tech’s intuition. If you think it’s the PSU, don’t trust the tester, try swapping it out with a known good part. This goes for other hardware tests as well.
My comments weren’t meant to come off as a dig to the author, but rather to express that I feel those power supply testers aren’t really all that useful.
As CompuClinic stated, they will show you a 100% dead supply when LED’s are not lighting. However they stop there, I’ve had power supplies be bad even when a fairly decent ($20) PSU tester passed it.
Same as SMART info for a hard drive. They will show you dead drives, but can pass working drives with problems.
A tester does not replace thinking or a tech’s experience. Of course you can have a false positive. But you will seldom have a false negative. The the time you save quickly replacing 50 PSUs is well worth the investment. If it shows bad, you can replace it without guilt or wonder and in much faster turn around than checking a dozen other things.
To quote mister Myagi “a Drivers license does not replace judgement.”
I have to agree with most comments. I have 2 cool max psu testers a chinese light led model and i remember one psu was reading fine on the cool maxs, but was faulty and could you guess the chinese one showed it was faulty.
Sometimes you have to go that extra mile. Good tools to have, but dont always solve the problem.
I bought a few of these
take a look and see what you think
http://www.ebay.com.au/itm/POWER-SUPPLY-TESTER-HDD-SATA-20-24-PIN-PC-PSU-ATX-/180449493418?pt=AU_Components&hash=item2a03a0c1aa
http://www.ebay.com.au/itm/THERMALTAKE-DR-POWER-POWER-SUPPLY-TESTER-/251053000929?pt=US_Computer_Power_Supply_Testers&hash=item3a73ecc8e1
http://www.ebay.com.au/itm/New-1-8inch-LCD-PC-20-24-Pin-SATA-HD-PSU-ATX-ITX-Power-Supply-Tester-New-/190835982634?pt=AU_Components&hash=item2c6eb6012a
* different types and all work 100%
http://imgs.inkfrog.com/pix/fubiao2011/10801874-6.jpg
http://img.inkfrog.com/pix/kangdigital/supply3.jpg
new one for me I want still
http://i.ebayimg.com/00/s/OTI0WDc2OA==/z/qA0AAOxypthRvFmV/$T2eC16Z,!)0E9s37HkLCBRvFmVf6kg~~60_57.JPG
I’ve tried more than a few PSU testers, some close to $25 in cost each, and none of them have been excellent in telling condition or quality of the PSU at the time. Nothing beats a quality multimeter for your bag, something like a Fluke device.
This is one area of technical testing that I feel no “fool proof” tester that the big boys make work too well for. Common sense and thinking on the tech’s part should be just as important as any tool you place in your hand. If you can extrapolate from the symptoms a machine is giving you, from deductive reasoning, you can usually make do without a multimeter as well in most cases.
While no PSU tester bought for less than $30 can be 100% accurate, they can be a pretty good indication as to what is going on.
With that said, let me tell you why I always choose a PSU tester with a voltage readout. There should be no more than a 0.3v variant with any PSU. The positive rails can be up 0.3v higher than spec, meaning a +12v can be between 12.0v and 12.3v. It should not be less (indicates bad PSU) or more (indicating a PSU on the way out. A negative rail can be 0.3v less than spec, meaning a -12v rail can be 11.7v to 12.0v. More or less than that range is indication of a bad PSU.
Note: An over voltage PSU should be replaced soon in order to prevent the proverbial “Pop” that systematically takes a component or two with it upon death. An under voltage PSU typically dies out slowly and doesn’t usually take out any other system components although, it should still be replaced as it too has a chance of damaging another component.
The article should be made into a flow chart. As some people have stated these inexpensive power supply testers don’t really do enough. They will only tell you if the power supply is bad (not good) and they lack any intelligent features. That said I do like the CoolMaz PS-228 (http://www.coolmaxusa.com/productDetailsPower.asp?item=PS-228&details=features&subcategory=powertester&category=powertester).
To really find out what goes into properly testing power supplies head over to HardwareSecrets (http://www.hardwaresecrets.com/article/Hardware-Secrets-Power-Supply-Test-Methodology/522).
Save time and just swap the offending PSU with a know working one. Fail safe and quick.
JP
IT support and services
A tester can tell you right away – it’s dead, Jim. Better to just run a 24 hour test to duplicate what the client is describing. Turn on, the machine dies after a few hours? Replace the unit with a good known dependable one and it stays on, you found the problem. Before throwing the old one away, save that pretty chrome fan guard!
I got my tester at frozencpu.com and they ship world wide.