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Basic PC testing for power problems

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Basic testing of a dead PC


I am going to explain the basic testing of a PC system when it will not power up.


1. The Power Good signal

There is a power signal that comes from the Power Supply (PS) to the mother

board (MB) even when the system is off, but not unplugged from the AC voltage. With this signal working the MB will turn on and operate. But if the PS and MB determine that a component in the system is not working, then the power will not activate the MB.


2. Power supply test.

Open the entire case so you can see clearly into the PC system. Make sure all the connections are plugged together and everything looks okay. There should be a little red light on the MB that is lit up. If it is not, then the Power good signal is lost. So let's test the PS first.

Unplug all add in devices from the mother board**, except the video card. Do this with the AC power disconnected from the PS. Then plug the AC back into the wall outlet. Check the red light on the MB again. If it is on, then plug in the HDD and check the light. If the light goes out

then the HDD is defective. If it stays on, then plug in the DVD, and check again. If it stays on, then go to the next device you have. The final step to this is the fans. Plug in the CPU fan first. Then so on. If the light stays on and all devices are plugged in, then hit the on/off switch on the case and see if it powers up. If it doesn't, then the power supply needs checking again.

Unplug all devices but the HDD and video card. Try to start the unit. If it runs and boots then we probably have a weak PS. Turn the unit off and plug in each device again, one at a time until the unit won't start. Make the fans the last thing.

If the entire test above doesn't make the system boot, then the PS is at fault. Replace it with one of at least 600W.

**Devices would be fans, dvd, harddrives (hdd), add-in cards, anything with a power cord to it.


3. Motherboard test.

The MB controls all aspects of power regulation in today's systems. This started with the invention of the ATX design in the early 2000's. This test is similar to the PS test above.

The exception is that the red light never comes on when power is supplied to the MB. Now to test this we have to remove the MB from the case. There is a unique thing that can happen in ATX systems. Ground fault interruption. This is where the ground of the MB thru the case actually shorts the system out. So to test for this, we have to remove the MB and PS from the case. Lay them on a clean dry hard no conductive table and plug the MB into the PS. Plug the video card into the slot and connect the power plugs. This should be the only thing plugged into the MB. Now plug the PS into the AC and see if the red light comes on. If it does, then unplug the AC and connect the HDD to the MB and see if the system starts up. If it does, then turn it off again and connect the CPU fan and restart. If you can connect the DVD and turn the system on and it boots then you have a ground fault within the case. To check this, re-mount the MB into the case and retry the power supply test. If it fails again, then we have to get rid of the ground fault. We do this by using nylon spacers for the mounting of the MB into the case. Replace any metal MB mounts with the nylon ones. This will isolate the MB from the case and it will only be grounded by the cables from the PS. This used to happen a lot with the mount nearest the keyboard connector for some reason. Another source of ground fault was the slot insert panel for the plugins that goes into the back of the case where the cables plug into the MB. But, most of the time it was a problem with the metal mounts.

In some rare cases the PS actually produces the ground fault problem within the case. You will find this when you use the plastic standoffs and the system still won't start. Replace the PS to alleviate this problem.

I have found that the DVD can usually stop a system from working most of the time. They are cheap and the circuitry fails often on the DVD. When this happens the DVD will produce a ground fault. The old floppy drives did this a lot.


4. IC chip problems


If you go through all the above tests and nothing helps to get the system to start at anytime, then you have a problem with the IC chips on the MB. These are referred to a lot as the chipset. They control everything on the MB. They are the brains of the MB. Everything you plug into the MB runs through these isolinear chips. They actually make your video card work, your HDD, everything. The one thing they do, is make sure the power is correct for the MB. The only thing you can do to fix this problem is replace the MB. These IC chips can be the cause of many video problems also. They can cause the HDD to malfunction in the writing of data to the HDD. Always update the chipset drivers from your MB manufacturer, along with the BIOS updates.


5. Correctly mounting a new MB.

If you have successfully gone through all the tests above and came up with the MB being the problem, and you have purchased a new MB, then it comes down to mounting it in the case and hooking everything up.

All of the systems I built in my business were of isolated power design. I used nylon snap in mounts for my systems, so that the MB was isolated from the metal case. I suggest that you do the same thing. You can get these mounts from any repair shop that builds and repairs PC's. Now most people will tell you that you don't need to do this, but I never had a problem with ground fault in the 6 years I was professionally building systems. I did fix a lot of other systems that failed in this area.

When purchasing these plastic standoffs, be sure to take one from your PC case with you so that you can match the height up.


Clean the CPU and the fan connection point with alcohol to remove the old coolant paste.

Mount the CPU and the CPU fan onto the mortherboard first, using a fresh application of coolant paste to both the CPU and the fan.

After you have screwed in all the standoffs that are needed for your MB, then place the MB over the plastic standoff and press down at each connection, starting with the ones at the front of the board where the cable plug in for the speakers, USB and other devices. Then work your way back from there. Once it is mounted then insert the wires for USB, MB connectors, and any fans that plug directly into the MB. Just follow the directions that come with the new MB.


6. Booting the new system


Once you have everything correctly connected, plug the cable into the AC outlet and check to see if the MB power good light comes on. If it does, then turn the system on and see if it boots. When it starts to boot, hit the <DEL> key to go into bios setup. At this point, just do a quick setup from the front page options list. Then let it boot thru to Windows. After Windows finds all the new stuff from the MB, restart at least twice to make sure it is going to run. At this point, I always go to the MB manufacturer’s site and get all the updates for that MB and install them. This includes drivers and BIOS updates. If you know how to manipulate the BIOS, then do that after you have updated the BIOS. Don't do any overdriving of the RAM or the CPU until it has run for awhile and you have tested the stability of the system.


7. New power supply.


If all the tests above come back with the problem being a Power Supply, then go to a reputable dealer and get one. If you have dual video cards, you will need at least 800W. If not, then 600W is good enough. Be sure to spend the extra money to get a good brand name one. Cheap unknown PS's produce erratic power and can cause even more problems. I use only Antec® or Cooler Master® power supplies. I have tested these PS with my own testers and they pass with golden numbers.


This picture shows how to hook up the MB to the PS out of the case. You will need a video card to make it work. This MB has a built in video card. But is basically the same.


The other picture shows the standoffs used in most cases. The middle one is for screw-in type as is the brass one. The other is a pop-in for certain brands of cases.




Edited by Fearless Staff
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