How do I test my PSU? Computer is dead



What’s a sure fire way to detemine if my PSU is at fault?

My HP Pavilion XL866 is dead…it does absolutely nothing. No sounds, no lights, no buzzing, no beeps, nothing. Dead as a door nail.

One would assume the problem is in the PSU, but how can I be absolutely sure?

There has to be a way to test the PSU to determine if it’s dead or not.

I don’t want to order a PSU if I don’t need one.

Please help.


Pull off the main 20/24 pin motherboard power connector then using a small wire or a paper clip connect the green wire with one of the black wires on the 20/24 pin plug, the psu should fire up and the drives will spin up, if not then the psu is dead. when you do this test there needs to be at least one hdd/odd connected to the psu since most psus have minimum load requirements to run.

some PSUs have a rocker switch on the back that cuts the power, be sure to check that out too, I’ve been guilty of thinking the pc was dead when that switch was off :o :doh:


The other way you can test your PSU is use a multimeter. Digital Multimeter you can buy it online or at a local Radio Shack depending where you live. Analog multimeters need calibration more as it ages while digital meters require it less (don’t short the leads on analog, you will mess up the calibration on it). Pocket multimeters come in handy and don’t cost much. Be careful though when you use one, I’m not responsible if you get electrocuted :wink: . But to test it you ground one lead and put the other lead onto the PSU power connector. The meter will give you a digital output of what voltage is being supplied from your PSU. If you don’t know how to do it you can follow this simple guide Guide


metal…I noticed the site was somewhat “dated” (2002), are the procedures still the same and are the voltages pretty much the same?

I believe this HP uses as a -3.3 voltage (my current one does) and I didn’t see anyh neg. voltages mentioned on the site you recommended I visit.

What are your thoughts on the -3.3 volts?

By the way, can I just unplug a molex and test across the black (if it has a black wire) and another hole to test to a voltage of any size to see if the power supply is still working? Or, can certain voltages be dead and others still alive and still have a dead PSU? Thoughts please.

I do have a MM and I have done some minor electrical work, so I know enough about voltages to be respective of them…but 12v DC shouldn’t even be felt.

But, believe me, I have a healthy respect for AC and you never know what a PSU is going to do. I will be very careful.


Yes, procedures for testing voltage remains the same (used to be an Electrician :wink: ). The only difference you will see is between ATX & ATX 2.0. Are you testing 3.3v line to ground? If you are, then that is how you are getting the -3.3v. Because you take one lead and touch it to ground and the other lead and touch it to the 3.3v, you get -3.3v. It’s trying to draw a load and the voltage has nowhere to go because ground has high ohms (lots of resistance to voltage). If it’s anything other than -3.3v when testing lead–>ground & lead–>3.3v line.

Testing anything to ground works the same way. For instance, you test a regular electrical home socket, one lead to ground and one lead to power for each side you will get about 55-60 volts on each side so 55+55=110 volts or 60+60=120 volts. That is where you get your 110-120v home electricity. AC is easy to test for, DC is harder to test because you don’t know if it is setup in parallel or series. If it is parallel structure that is being used for the DC power then it is much more difficult to tell, if it’s series then it’s easy. You should be able to test straight across the main power connector and ground one lead to get the DC power coming out of each of the main power’s leads.

Oh, and one last thing, voltage is not what kills you, it’s the amps that kill you (most people will think the volts kill you :disagree: ). However, as a former Electrician, I don’t recommend touching anything that is 30VDC or more. It is considered unsafe. It only takes a tenth of an amp to kill you while you can get shocked with 500 volts from a megger and live because there’s no amps. A co-worker shocked me with 500 volt megger before. It hurts but it won’t kill you. (watch out for those sneaky electricians, they like to play tricks on you)


Yes, I forgot it’s the amps you have to watch out for. Guess I’m getting too old and forgetful. Thanks for refreshing my memory. My bad as the youngin’s say.

The LiteOn Power Supply (HP Part No. 5184-3961) that came in the HP Pavilion XL866 AMD computer I’m trying to get up and running has five (5) voltages: +5V; +12V; -5V; -12V; +3.4V; and +5Vsb (what does the small “sb” mean on this voltage?).

I was trying to find out how to correctly check this PSU to see if it’s the problem (dead computer). Someone told me you could damage the PSU by disconnecting everything and testing it that way…he said the PSU has to have a load on it or it won’t test right…what do you think about this comment?

By the way, what’s the difference in testing an ATX verses an ATX 2.0 and what’s an ATX 2.0?

Does anyone know where I can find a replacement HP Part No. 5184-3961 PSU assuming this PSU is the culprit?..I’m thinking it is. The PSU says the voltages must be as follows (this PSU has the following on the sticker)
+5V/25A Max
+12V/4A Max
-5V/0.3A Max
-12V/0.5A Max
+3.4V/16A Max
+5Vsb/1.5A Max

It also says the +5 and the +3.4 voltages cannot exceed 25 Amp. This must be pretty important to put it on the label.

I must have these numbers before I buy, please advise if you know of a place that sells these. I’m not having any luck finding the exact same PSU. Does it really need to be exactly the same? This is an important question because I’ve found several but the amps for the corresponding voltages are not the same as what I need but they say it’s a replacement and is warranted to work. Go figure.

This is the right HP and LiteOn part number and the right wattage.

I just need to be sure it the same thing I need. The voltages and Amps need to be the same as my old one.

Metal, why can’t I just check the output of one of the molex connectors? If I get no voltage there, shouldn’t that tell me the PSU is dead? What voltage should a molex give me?

I’m also confused as to why I need to test at the 20 pin connector instead of just testing at a molex connector. Can you explain?

Why do you jumper the green pin to a black (ground) pin? Almost forgot to ask.


I am assuming there is a typo in the specs as the 12v is no way only 4amps
most likely you meant to post 14 amps. If this is the case, and you have added hardware to the system ex: another hd/ cd/ dvd then you need a bigger power supply anyway.


No typo my friend. This is what it is, a shot of the label on the PSU. I hope you can see it clear enough. See the attachment.

And, nothing has been added to the computer…it’s just as it came from the manufacturer.

Can you help me find a replacement PSU with these spec’s?



Burnselk - does the fan inside the PSU turn at all? I assume XL866 is 866 MHz, right? It’s not under warranty, correct?

A standard drive connector should have 5 and 12 volts, positive and negative may be printed on one of your drives (I don’t remember the pinout). Check one of the spare Molex plugs, or unplug the CD or DVD player / burner and use that one. As for checking 3.3 volts, sorry I can’t help.

I lost a motherboard by using a cheap PS once. I installed a higher quality brand in my main PC, and haven’t had a problem since. Two power supplies may both promise 350 watts for example, but the good one has more amps at each voltage and will give you the full 350 before it fails.

I hope you get your PC back up quickly.

And yes, do be careful around electricity.

you will get about 55-60 volts on each side so 55+55=110 volts or 60+60=120 volts. That is where you get your 110-120v home electricity.

I just tested my outlet with my Fluke 16 (I’m in Heating and Air Conditioning). Hot to neutral = 121.8V. Hot to ground = 121.8V. But neutral to ground, zero. (Neutral and ground should be wired together at the circuit breaker box, IIRC.)

When I checked the 240 volt outlet (electric dryer) I got 121.8, 121.9, and 243.7. This might have been what you were thinking of. One of my mates in HVAC night school, “Sparky”, learned this the hard way. (And just for the record, I did not start that fire. That was another guy).

I believe “sb” is “standby”. I think this is only important if you set the power saving features to wake up when the mouse is bumped, etc.

It may be impossible to find such a low-power (188 watts!!) power supply these days. And if you are using a CD/DVD burner (or you wish to add a SCSI chain), you will likely want to replace it with at least 250 watts.

(In fact, some high-powered “gamer” video cards suck so much power they require their own Molex connector right on the board!)

Take care.



Sorry to reply to myself, but the darn software won’t let me edit after 30 minutes (I really, really hate that), and I have some more stuff.

burnselk - if it makes you feel better, I have an old 800 MHz Gateway, I think they only made the PS good enough to get it out the door. It looks like it could fail at any time.

I would print out or draw MetalSlayerX’s diagram (for buying from a brick and mortar store, or ask if purchasing a new PS from an online vendor). I did not know there were two types of ATX connectors. You want to make sure you get the right one.

(In the late 1990s, Dell made some PCs with power supplies that were not standard, to get you to buy replacement parts from them. Thankfully this isn’t one of those machines.)

It sounds like the power supply is dead. But it sounds like you know enough to put the new one in pretty easily.

EDIT: I really, really, really, really didn’t start that fire. Really :slight_smile:

Take care.


As I said, the computer does nothing…no fans, no lights, no buzzing, no humming, no whirling, nothing, zip…the computer does nothing at all.

This computer was purchased new in Feb 2000 and has an AMD Athlon 1.1GHz processor. Nothing has been changed in, or added to, this computer.

I guess my big question is this (assuming the PSU is bad): Can I install a larger (188w would be hard to find anyway) PSU in this computer that has different voltages and amps?

I’m more concerned about the voltages and the amps than the power…I guess what I’m saying is I don’t want to fry any parts (mostly the mobo) by installing a PSU that has different voltages and higher amps. This computer wouldn’t need more than 200 watts…most used (pulls from working computers) PSU’s I’ve looked at have much higher amps than this one. I doubt I’ll ever find an exact replacement…so, I need advice about replacing this PSU.

Can someone advise me what to do? Calling HP is of no help at all…tech support today is at best a negative experience. I can learn more from this forum than from anyone.

Saturn…thanks for the meaning of “sb”…that makes sense…never thought of that.

Metal…or anyone here…can I use a PSU (new or used) that has different voltages and different amps than the one that came in this computer? See the label on the PSU above. Thanks to all who reply!! I’m asking for help guys…I really want to fix this computer for my father-in-law…it will be such a great gift for him.


Wow, never seen a supply with a 12v that low—that I can remember, how old is that system?

Just because it is a higher rated PS, doesnt mean it it will push that much power into your existing setup, it just means that it can handle that much power. Try one of the ones you pulled , as long as it fits in the case and the rails are higher than what you current have. Low power is worse on a puter than anything, besides a lightning strike! lol this seems to be about what you need to replace the one you have for a decent price.good reviews.

See I smoked a 430 watt Antec recently, but it had been pushing alot of power, probably more than it could handle with the rig in me sig, so I bought a 650 trio and man what a difference it made. No more crashing and refusing to boot up…lol

If you get good quality PS with 350 -400 volt range and decide to add more drives and such you will be ready to go already.
Do you plan on building your own rig sometime soon? If so, try and get one that will handle what you plan on upgrading to.

  1. It’s possible that you can damage a PSU but I can’t vouch for that as I have never damaged one testing it. Incorrect, the PSU can be tested without a load by jumpering green to black. The part you can’t test is the measuring of the voltage. It needs a load for that part.

  2. ATX has 20 pins and ATX 2.0 has 24 pins, newer motherboards need the 24 pins for the extra 12v rail power.

  3. There are plenty of links for a similar power supply that can replace your PSU. As far as I know from reading the links, your PSU is not manufactured anymore because of expensive costs. And yes, you can use any 20 pin PSU, it doesn’t have to be the same but make sure it has equal to or greater watts than the original PSU. However, if you would like to save the cash you can buy the same PSU, OEM manufacturer tend to all use cheap PSU’s. The ratings that are rated on the PSU are there to tell you how much amps you can draw. The ratings just gives you an idea of what you could upgrade in your PC. Any PC with extra added parts will need extra power.

These are supposedly the alternative replacements for your PC’s PSU.

  1. You can’t test the molex because the main power needs to draw a load on it. Otherwise you will get .9 volts or less. If it does have a load then on the two outer most connections on the molex should read 12v and 5v.

  2. Jumpering green to black makes the PSU not require a load to run it. The PSU should power up but I don’t recommend repeatedly doing the process for testing as that’s not good for a PSU. Basically it’s a way to bypass the protections on the PSU. (see example image, hand drawn on Tablet PC :stuck_out_tongue: ) A lot of electricians use jumpers to bypass protection mechanisms. I’ve used it many times but only as a last resort. By jumpering it, your fan on the PSU should start to spin. If it doesn’t spin then your PSU is definitely dead or may require some parts on your PC to be connected ie. CDROM, PCI Card, etc. to give it some load. Most PSU’s from OEM manufacturers don’t last long.

If you want to go the less expensive route, you can buy a similar PSU. Or for a little more you can get a quality PSU; just make sure it fits your case because I think most older OEM PC’s use MicroATX cases.


wow that is a crazy low psu for that system :eek: my old 233mhz gateway from '97 had a 200W w/6A on 12v

as has been said, as long as the new psu fits in the case it should work, all newer psus are compatible with both 20 and 24 pin mobos with either a split plug or an adapter


The PSU has a note on it saying “[U][B]The +5 and the +3.4 voltages cannot exceed 25 Amps[/B][/U]”.

This must be pretty important to put it on the label.

What do you think about this? Would you be concerned about it?


that is stating that the draw on the 2 rails cannot exceed that amperage (or it will fail basically)


Tell me if the following is what you’re telling me:

If the combined amperage of the two voltages (+5V and +3.4V) is greater than 25, the PSU would be fine to use in this computer. Is that correct?

But, if these two voltages have a combined amperage lower than 25, the PSU would not be OK for this particular computer. Is this also correct?

If the above statements are true, I believe I’m beginning to understand the amperage issue with PSU’s and computers.

If the amperage for any of the six (6) voltages of the replacement PSU is less than what the original PSU calls for (see label above), the replacement PSU should not be used because it would most likely fail. Is this also correct?

If I am under the wrong assumption, please set me straight…anyone.


I found the following PSU for sale on Ebay…notice it does not have a -5V output but it says it replaces the PSU in my computer. See the attachment.

Computer PSU.doc (22.5 KB)


Most PSU’s have a combined load limit…

“The +5 and the +3.4 voltages cannot exceed 25 Amps”. - actually means that the power supply has a pretty sever combined limit, where the 3.4V and 5v Amperages actually come out of the same limit… 25A Max on 5v, 16A max on 3.4v, but 25A max combined across both - basically meand that those two are driven from the same section, with absolutely no reserve.

It’s a maximum load limit for the PSU - most of the time they now mark the combined load limits in watts rather than amps, but it’s rare to find a PSU that CAN deliver 100% on all rails simultaneously.

Another thing, this calls it 3.4v, while most current PSUs are 3.3v - that is probably within acceptable tolerances.

It’s also possible that the original PSU is not a common standard at all.


What do you think the -5v output on the PSU is used for? Any clue?

Guess I’d better make sure a replacement PSU has the -5v output.

If you were looking for a replacement PSU, would you want the volts and amps (for each) to be the exact same/close, or would you want it to have more amps than the max for each voltage?