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CPU Failure, Motherboard, or something else?

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15 replies

by reggiefor

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I am trying to diagnose a friend's PC problem (desktop).

Symptoms:
PC powers up, loads OS (WinXP), works for a few minutes -- I can start running a program or look at computer properties -- and then it seems to die. The video input blanks out -- the indicator light on the monitor goes from green to yellow.
Sometimes the video doesn't even start up.
It sounds like the HD is still spinning. The fan remains on. The power supply is only a few months old.

When I pull the monitor cable from the back of the PC, the monitor lights up with a "check signal input" message. This leads me to believe that the monitor is being "told" to blank out and go into power save.

I tried to start installing a new video card (current video is on board and I happen to have a spare video card on hand), but I can't keep the video running long enough to install new drivers. I currently have the HD pulled out and hooked up externally to my laptop. It seems to spin fine and I can read it. I'm running antispyware scans on it just in case. I'm pretty new at this level of hardware evaluation and I am stymied. What do I try next?
If more information would help, please tell me what you need to know.
Thanks.

15 replies

by oh smeg

It could just as easily be a Software Issue.

Try some form of Live Optical Disc to run off and see if the Video stays on. If it does it's not hardware but a software issue occurring here.

You can use a Live Linux

http://www.livecdlist.com/

A diagnostic Disc like the Ultimate Boot CD

http://www.ultimatebootcd.com/download.html

to do this or any Disc that you can boot off without loading the OS in use on this computer.

Both of the above listings are free to download though the Live Linux Link will redirect you to the individual downloads of the different listed Programs.

Col

by reggiefor

Sorry. I should have included that I did try UBCD4Win and the video still cut off after about five minutes.

Does that spur any other thoughts or a possible diagnostic course of action?

I appreciate your help.

Reg

by oh smeg

Runs inside of Windows and is not a valid rest for the Hardware.

You need to run something from a Boot Disc with it's own display settings and not rely on anything inside of Windows here.

But if you are certain that it is hardware related start with the more obvious things.

Crack the case open and clean it out. Pay attention to the Heat Sinks on the CPU and on the GPU of the Video Card.

You can blow the dust and other crud out of the system with Low Pressure Air but [b]Do Not[/b] allow the fans to spin as they will generate electricity and this will damage the M'Board.

As the PS is fairly new here what brand is it and has it taken any hits from Power Spikes? A PS can be killed in under an hour if it is exposed tot he wrong environmental variables. Power Spikes from heavy draw electrical equipment or Damage tot eh Mains Feed can kill a PS in under a Nanosecond. I have had brand new Antec PS's die while on the test bench and that has always been attributable to severe Power Spikes that get past the Filters. That's part of the reason why I do not do any work during thunderstorms ever.

No name Power Supplies can pass these Spikes straight through and degrade/destroy the Internal Electronic Components so you need to look at the actual Power Supply and make sure that it is really working. The only real way to do this is to test with a [b]Known Good[/b] Power Supply.

Just as an after thought have you tried a different monitor? I got caught out with a system where the Video was supposed to be turning off when one of my monitors died. It would run for about 30 minutes from cold and then turn off to Power Saving Mode. If you turned off the monitor and then back on it would then display a picture from anything from 30 seconds to several minutes depending on the heat. The hotter the room the shorter time the monitor would stay on but when it was unplugged it would show the No Connection Display.

Col

by reggiefor

In your first reply, I thought you recommended UBCD4Win. Did I misunderstand? I booted from a cd w/ UBCD4Win on it.

I did clean out the case and, with power off and cord disconnected, blew out dust w/ low pressure air. The case was surprisingly clean to start out with; but I did find some crud. Alas, it did not help.

I'll take a closer look at the heat sinks. I am still testing for spyware.

Thanks.
R

by oh smeg

Which is one of the suggested Boot Disc's that I gave you and suggested Booting off that.

There was no mention of the UBCD 4 Win in my post.

Without a HDD in the case insert a Boot Disc and boot the system. If the video goes out now you have a Hardware Issue but if it stays on you have a software issue with Windows and the Video Driver or at the very least something conflicting with the Video Driver as things load after Windows Opens.

Col

by reggiefor

I saw UBCD and assumed that they were all created equal. I'll try your link. The HD is out of the box already, so I'll find out soon.
Thanks.
R

by reggiefor

Ok -- I created a UBCD and started running a CPU test. I got one line of output: spurious interrupt 8259A IRQ7. I walked away for two minutes and by the time I got back the video was off again. So, it's not Windows.

I know the HD is fine. I'll try switching out the PSU, but I really don't think that's it. I'll repost once I do that, but if anyone has any other ideas, let me know.
R

by rob miners

and disable the onboard Video before fitting the new card.

by tintoman

Because I repaired a PC with exactly the same problem just last week.
It was the PSU at fault.
Obviosly it would be better to swap out with a spare if you have one to verify this but there lies my bet

by ---tk---

of the PC? Hopefully its not a dell GX280 or GX270... Those older ones are notorius for blowing caps...

by nicknielsen

1. Power supply. A good repair shop should have a tester (http://www.amazon.com/gp/product/B000V6Y7L6) that can verify PSU operation.

2. Defective main board components, usually capacitors. The capacitors are trash-can looking things - image at http://www.capacitorlab.com/capacitor-types-electrolytic/radial-capacitor-polarity.jpg - that tend to swell if they overheat. To check the capacitors, use a combination of visual and tactile inspection. First, focus a penlight on the top of each capacitor; it should focus the light back to you. If you see light reflected from only one part of the top, the capacitor is most likely bad. You can verify this using the tactile inspection. Run your fingertip across the top; it should feel flat or concave. If it feels like it pokes up or bulges, the capacitor is bad and must be replaced. Again, a good repair shop should be able to do this for you.

by daveaaa3

Also, simplify things a bit. Run with just power supply, keyboard, motherboard, and monitor and see what happens. Divide and conquer. I'm betting the power supply, too. Better hope it's that, otherwise it's new motherboard time.

by oh smeg

Start with the easy things swap out the PS. Even the better PS Testers are no real guide to how well the PS may be working as they can not test the PS under load.

While they are a good guide I've still had PS's that test OK and do not work when fitted to a case.

As the others have already said if it's not the PS it's the M'Board and or CPU here which is causing this to turn off as as you have On Board Video I would be looking at the Electrolytic Capacitors that Filter the CPU Voltage.

But to be perfectly honest if it's not the PS it's expensive and maybe not worth the cost of repair depending on how old this is.

Col

by jmcphee6089

May be an obvious answer, but are you sure that any smartfan settings in the BIOS are set correctly? If not, the system could be shutting down or going to standby based solely on the processor going past a designated temperature because the cooling fans aren't running properly. Thus the signal to the monitor gets killed at random times, but all within a few minutes of starting up. It happens a lot in E-machines...

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