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Computer wont turn on


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#1 DarknessConsumed

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Posted 30 November 2008 - 05:12 PM

My friend brought me his computer that wont turn on. I tested the power supply and it works fine but i cant get any power on the computer. When i plug a power cord to the computer i get the pilot light on the motherboard to light up so i wouldnt think its the motherboard. Is there anything else that could be the problem or any tests i can do to find out what is wrong?

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#2 hamluis

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Posted 30 November 2008 - 05:29 PM

Fans do not spin?

Desktop or laptop?

Louis

#3 DarknessConsumed

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Posted 30 November 2008 - 06:39 PM

it is a Dell Dimension 3100 Desktop. Fans do not spin. The light on the mobo cuts on when i plug it in though. is there any way to test the mobo to see if that is the problem? or is there anything else it could be?

#4 garmanma

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Posted 30 November 2008 - 06:58 PM

Don't pay any attention to the motherboard LED. Chances are the power supply
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Caution: There are electronics inside the case that are very susceptible to electrostatic discharges. To protect your computer, touch the metal of the case to discharge yourself of any electrostatic charges your body may have stored before touching any of the components inside. As a safety precaution you should unplug the computer to avoid electrical shock.
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The purpose of this procedure is to bypass the motherboard to test the PSU.

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.

Posted Image

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.

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.
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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 of the given values.

Yellow +12VDC

Blue -12VDC

Red +5VDC

White -5VDC

Orange +3.3VDC
Mark
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#5 DarknessConsumed

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Posted 30 November 2008 - 07:13 PM

Ive done the green and black wire test. All the fans and stuff cut on. Any other ideas?

#6 hamluis

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Posted 30 November 2008 - 08:28 PM

Reseat...the video card, if any...RAM.

If adventurous, you can examine the CPU for bent pins and thermal grease/proper fit.

Since you have his computer and yours...switch your PS into his system (I hope we are working with desktops) and see if it fires up. Ditto for various equipment items until you can eliminate something or confirm a problem with something.

You can run Memtest on the RAM, a diagnostic on the hard drive.

Louis

#7 DarknessConsumed

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Posted 01 December 2008 - 01:02 PM

The computer has the built in video card...i took out each RAM card and tried them both in both spots and still get nothing. I checked the processor and that all looks fine. no pins in the processor chip to bend...I unhooked all hardware in the computer, cd rom, dvd burner, media reader, etc. and tried without any of that and still nothing, i checked the battery on the mobo and put a new one in it and got nothing. Is this a sign that the mobo is gone? I cant really think of anything else that it could be. I would try a different PS but none of the PS i have on all 7 computers in my house are the same hookup as his.




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