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PC won't turn on - how do I troubleshoot components?


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#1
DjFonti

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Hello all.

Recently I've been doing upgrades to my PC.

Today my new case fans, fan controller and graphics card arrived.

I installed the graphics card and powered on and installed the drivers and everything worked fine.

I then installed the fan controller in to the 3.5" floppy bay, and connected one of the new fans to test to see if the two components were working - both worked fine and the fan speed responded to the controller.

Great I thought, I'll install the final fan, connect it to the controller, pop the lid back on and I'm done.

I did this and pressed the power on button. No response :D . All that happened was the red HDD activity light flashed for a fraction of a second but nothing was powered, no fans or anything.

I was using an antistatic wrist strap the whole time.

I have now removed the PSU and tested it with the 'paperclip test'. I connected a fan and bent a paperclip in to the green wire and adjacent black wire on the 24-pin motherboard connector. The fan powered up fine, so I guess this means my PSU is fine (it is virtually brand new and a Corsair as well).


So what do I do now? I am guessing the motherboard is the next logical thing to test but how would I do this?

I'm dreading the system somehow being fried because there are a fair few new components in it.....

I would dearly appreciate any help with this, it's a real blow ;)

Thanks for reading and I appreciate any help.


EDIT: I don't know if this is relevant but I'll include it.
When I installed the fan controller, I connected one molex connector to it, and used one of the three fan controller wires to connect to the one fan and it worked. When I added the second fan, all I did was connect it the same way, to the 3-pin fan controller wire....so now there is one molex in to the fan controller and two fans connected. Could this have caused the problem? Because the one molex would have been powering one fan conroller and two fans, I did not connect seperate molex connectors to each individual fan.

Edited by DjFonti, 14 December 2010 - 06:30 PM.

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#2
Digerati

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That in no way is a conclusive test of the PSU. In fact, it is dangerous one. There is no standard color coding for PSU wiring. While Corsair is certainly a name brand, it could still be bad. Note that fans spinning only indicates the presence of +12VDC. The PSU must also provide +5V and +3.3V.

Here is my canned text on testing PSUs:

To properly and conclusively test a power supply unit (PSU), it must be tested under various realistic "loads" then analyzed for excessive ripple and other anomalies. This is done by a qualified technician using an oscilloscope or power analyzer - sophisticated (and expensive) electronic test equipment requiring special training to operate, and a basic knowledge of electronics theory to understand the results. Therefore, conclusively testing a power supply is done in properly equipped electronic repair facilities.

Fortunately, there are other options that are almost as good. I keep a FrozenCPU Ultimate PSU Tester in my tool bag when I am "in the field" and don't have a good spare power supply to swap in. While not a certain test, they are better than nothing. The advantage of this model is that it has an LCD readout of the voltage. With an actual voltage readout, you have a better chance of detecting a "failing" PSU, or one barely within specified ATX Form Factor Standard tolerances. Lesser models use LEDs to indicate the voltage is just within some "range". These are less informative, considerably cheaper, but still useful for detecting PSUs that have already "failed". Newegg has several testers to choose from. All these testers contain a "dummy load" to fool the PSU into thinking it is connected to a motherboard, and therefore allows the PSU to power on, if able, without being attached to a motherboard - great for testing fans, but again, it is not a true load or suitable for conclusive testing.

Note the required voltage tolerance ranges:

Posted Image
NOTE: Disregard the -5VDC reading. It is no longer used.


Swapping in a known good supply is a tried and true method of troubleshooting used for years, even by pros. If you have access to a suitably sized, spare power supply, carefully remove the suspect supply and replace it with the known good one, and see if the problem goes away.

I do not recommend using a multimeter to test power supplies. To do it properly, that is, under a realistic load, the voltages on all the pins must be measured while the PSU is attached to the motherboard and the computer powered on. This requires poking (with some considerable force) two hard and sharp, highly conductive meter probes into the main power connector, deep in the heart of the computer. One tiny slip can destroy the motherboard, and everything plugged into it. It is not worth the risk considering most multimeters, like plug-in testers, do not measure, or reveal any unwanted and potentially disruptive AC components to the DC voltages.

The voltages can be checked in the BIOS Setup Menus of most motherboards but they do not reveal ripple or other anomalies either. And the Setup Menu places very little demands on system resource so, like the temperature readings found in BIOS Setup Menus, they may not reflect values obtained when the computer is processing demanding tasks.

And remember, anything that plugs into the wall can kill. Do not open the power supply's case unless you are a qualified electronics technician. There are NO user serviceable parts inside a power supply.


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#3
DjFonti

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Hello Digerati and many thanks for the informative reply.

Not having the time or money (this close to Xmas) I can't get one of those testers. Thankfully I still have my old PSU, the one the Corsair replaced.

I swapped this in connecting just the motherboard and CPU, and it seemed to switch on. To be sure I connected the boot drive as well, and sure enough the PC booted up and I was able to access Windows and shut down. I didn't have all the components connected as before to this PSU because I just wanted to test if the PC would power on, and didn't want to overload it as it old and is only 250w. But despite this, is it safe to assume that it's the new Corsair PSU at fault?

Would it be unwise to pop the Corsair back in to see if anything has changed? I have to be certain it is faulty if I want a replacement issued.

I appreciate any help, thanks.

Edited by DjFonti, 15 December 2010 - 05:33 AM.

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#4
Digerati

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I would be hesitant to put that Corsair back in without testing it first. While it is possible you just had a loose connection before, you cannot be certain. And while certainly Corsairs are among the best PSUs made, a faulty PSU can destroy anything it plugs into. So it would be sad, and expensive, if you tried it again and it destroyed your motherboard, CPU, RAM and graphics card too.

Note that some shops will test a PSU for a nominal charge or may even plug in a tester for free. Again, those testers are not conclusive, but if they report all voltages are present and within tolerances then I will feel more comfortable putting it back in service.
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#5
DjFonti

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I see what you're saying. The shop is very specific saying that all products have to be in perfect condition if a refund is to be issued. The PSU has a couple of small scratches so if they report it's working for them I may have to take it back and then I won't know what to do with it.

I will ring a couple of local repair shops and see if they could test the PSU for a small price, hopefully they can help. If not, I guess I'll just have to deal with what the shop says.

Thanks for your help. :D
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