BleepingComputer.com: Power supply

Hi! I`m new at this.So bear with me. My friend has a Compaq Presario SR1810NX,and it will not turn on.The computer is 4 years old and doesn`t get used all that much.Nothing new has been added to it.It just quit working.I blew the dust out of the power supply and the rest of the computer. It wasn`t that bad.When I push the start-up button the green light goes out and the fan turns a couple of times then stops.Is the power supply ka-put?

Hi Pinestump, and welcome to BleepingComputer.

There are a couple of things that could cause this. If the CPU was over heating it could shut down the computer. Or some component failed during the POST.

To determine if this is the PSU or not you can use the following test. If the PSU comes on and the fan spins inside it, then there is a good chance that it isn't your problem.


Caution:This procedure will involve working with live 12VDC electrical potentials which if handled improperly may lead to electrical shock. Proper precautions should also be taken to prevent electrostatic discharges (ESDs) within the case of the computer. For safety purposes please follow the instructions step by step.

First, shutdown your computer. Then unplug the power cable going into your computer.

Once you have opened the case, touch the metal of the case to discharge any static electricity.

The connector of the PSU which connects to the motherboard is readily recognizable by the number of wires in the bundle. To disconnect it you will need to press on the plastic clip to disengage it and then pull the connector up and away from the motherboard. Please take notice of the location of the locking tab and the notch on the socket of the motherboard, this will only connect one way as it is keyed. This wire bundle will have a memory of the way it has been installed and will want to bend back that direction, you may have to play around with it to find a position that the connector will stay in the same position while you run the test.



From the top left to right the pins are 13-24, the bottom from left to right are 1-12.


Please notice that there are PSUs with 24 pin and 20 pin connectors, the location of the green wire in the 24 pin connector is #16, and the green wire in the 20 pin connector is #14. If you look at the connector with socket side facing you and the clip on the top the number one pin will be on the bottom left corner. This makes the pin out for the 24 pin connector from left to right 13-24 on top, and 1-12 on the bottom. The pin out for the 20 pin connector from left to right is 11-20 on top , and 1-10 on the bottom. If you look at the connectors you notice that these are sockets that fit over the pins on the motherboard where the PSU cable attaches, this is where you will place the jumper. For a jumper you will need a piece of solid wire about the size of a paper clip (20-22 awg), preferably a wire with insulation. It will need to be large enough to fit firmly into the socket so that it will not need to be held in place while testing. You are at risk of electrical shock if you are holding the jumper when you power up the PSU. Insert one end of the jumper into the socket of the Green wire, and insert the other end into the socket of any Black wire.

Once the jumper is in place plug the cord back in. If the PSU is working properly the case fans, optical drives, hdds, and LEDs should power up and remain on. I would suggest that you not leave this connected any longer than is necessary for safety purposes.

At this point you can use a DC Voltage meter to read the different rail Voltages. You will want to insert the black probe into any of the Black (-) sockets, and insert the Red (+) probe in the five different colored sockets, one at a time. Below are the five different colors and their corresponding rail voltages. The Voltages should be within about ten percent plus or minus of the given values.

Yellow +12VDC

Blue -12VDC

Red +5VDC

White -5VDC

Orange +3.3VDC

To reconnect the 20/4 pin connector unplug the power cord, remove the jumper, and reconnect the connector. Take a moment at this time to make sure that nothing has been dislodged inside the case.

Please post your findings back here.

This post has been edited by dc3: 24 September 2010 - 11:07 AM

Made a jumper,Plugged the computer in. Power supplys green light and fan came on.. No other fan came on.Nor could I hear the Hard drive power up. I don`t have a meter to measure current.So I went ahead and unplugged all the plugs from the motherboard and plugged them back in.Removed Both memorys and replaced in slots.after I put everything back together.I unplugged the CD/DVD Drive and Hard Drive.I plugged the computer back in and the power supplys green light and fan worked.I unplugged the computer and plugged the CD/DVD drive and hard drive back in.Buttoned everything back up plugged computer back in and everything WORKS. I`m not much on Electronics so what happened I still don`t know.I want to Thank You for your help.I put this site in my favorites for future rsference.Any Ideas as to what might have caused the problem?Just a wild guess will do.Again Thank You!

This post has been edited by Pinestump: 24 September 2010 - 05:49 PM

It's hard to say. From what you have written it could have been a loose connection, or an intermittent problem that will raise its ugly head again. I swear... at times I think the machines are just trying to lul us into a false sense of security.

Seriously... I hope this solved your problem.

This is where we in the business call it a "Ghost in the Machine" IE: no reasonable explanation why the computer failed but now everything seems to be working ok.

My friend and are from an era before 8 track tapes and computers are still pretty complex for us even though we both have had them for about 4 years.One more question then I`ll leave you to help some other lost soul.My friend has a bad habit of not keeping everything updated on his computer(the one that failed).Over time could this bring a computer down?

Pull the side cover and check for bulged/leaking caps on the motherboard.

Not keeping a computer up todate usually causes.problems only when trying to run new software, new hardware, or if its a security patch.

"Made a jumper,Plugged the computer in. Power supplys green light and fan came on.. "

All that proved is the power supply is getting power .

Many times a bad power supply will still "come on" & make the fans spin.

HP/Compaq mostly use rebranded "Bestec" power supplies.
Bestec PSUs are best known for going bad & frying the motherboard in the process.
They will still appear to come on though.

[Bestec PSUs is what has given Emachine a bad name]

If you really want to know if the computer still works get a known good PSU & try it.

If you go back and read the introduction of that article is states that the purpose was to bypass the motherboard to determine if the problem initiating the PSU was with it.

When the PSU 20/24 pin connector is removed from the motherboard, and the PSU is turned on, there is power to the peripheral devices. You can demonstrate the presence of voltage with a optical drive by opening the tray, the motor is 12V DC.

Dell is the company that is notorious for using Betec PSUs, and a large number of these did fail.

The point of my post was that a PSU can appear to work & still be bad.
Jumping a couple of connectors with a wire simply allows the PSU to function, good or bad, without being attached to the motherboard connector.
The only real way to determine if a PSU is functioning properly is with a proper PSU tester.

I have fixed enough emachine, HP, compaq & dell with "working" bad PSUs to know that because it comes on & supplies power doesn't mean it's "good".

I wrote in my last post that In the introduction of that article it states that the purpose was to bypass the motherboard to determine if the problem initiating the PSU was with the motherboard.

By itself, this procedure wasn't intended as a voltage test. But if a multimeter set to 12 Volts DC is used in conjunction with this test the rail voltages can be read very accurately. More accurately than a PSU tester which most only provide a pass/fail readout which is rated to be within 1% +/- tolerances. Most manufacturers of PSUs allow for a +/- variance of 5%.

I think the power supply just needed to be drained of capacitance and let it reset it's logic. :D First thing I always do is unplug the power cord and press the power button on the machine to discharge it.

Well it raised its ugly head again.I took it back to friends house and connected everything back up.I started it back up and no problem.At my house I must of turned on and off a dozen times and it always came on.Turned it off at my friends house and it wouldn`t come back on.Sooo,the only thing different is when I was doing it at my house was I didn`t connect the speakers.At his house I connected his speakers.They are the speakers that came with the computer and yes I connected to the right place.I unplugged the speakers and unplugged the power for a few minutes,then plugged the computer back in and it started right back up did this a couple of times.And it always comes back on. where to from here? :

If this is happening consistently with the speakers plugged in, but consistently doesn't occur with the speakers disconnected I would suspect that there is a short somewhere either in the speaker system or the connection between the motherboard and the speaker jack.

If you have access to another speaker system try use that to see if the problem is the speakers or the motherboard and jack.