Bad Motherboard?

[drewm]

Hey, guys. I have what is probably going to be viewed as a dumb question. Certainly a newbie question if nothing else. I am working on a computer that I originally thought had a bad power supply. Basically, it wouldn't turn on. You could plug in the cord and there would be a click, the PS fan would very lightly blow briefly (maybe for half a second), another click and then there would be absolutely no activity. I got my power supply tester and ran a diagnostic. When I plugged everything in, it registered everything as normal and the computer stayed on like any other system would (obviously there was no display or processing as the motherboard had all but been taken out of the situation). My question is this: This sounds like the motherboard needs to be replaced, right? Is there anything else I can test first? Any input? This would be my first OTJ experience replacing a motherboard is the only reason I ask. What else could be wrong? I have also reseated virtually every piece of hardware in the box as a last-ditch sign of desperation. I am drawing a blank...

Thank you for any input you provide.

 

[NYJimbo]

Always post the make/model of computer, or if its a generic/custom then if possible the motherboard and power supply make/model. Any or all specific info helps.

 

[drewm]

This is a Dell Dimension 8400. It still has the OEM motherboard and I don't think they have had as much as a memory upgrade since they got the system. Sorry I can't provide much more information, Dell didn't want to print any real specifics on their motherboard. The power supply is a Dell, model number is N350N-00. Hope this is enough info to go on. Sorry.

 

[studiot]

I got my power supply tester and ran a diagnostic. When I plugged everything in, it registered everything as normal and the computer stayed on like any other system would (obviously there was no display or processing as the motherboard had all but been taken out of the situation).

Not sure I understand this,

What do you mean by

'the computer' stayed on'

 

[studiot]

I have seen the symptoms you describe with a faulty (usb) keyboard attached to an 8400.

Replacing this cured the problem.

 

[drewm]

I have seen the symptoms you describe with a faulty (usb) keyboard attached to an 8400.

Replacing this cured the problem.

There are currently no peripherals hooked into it. Only the power cord at the moment.

In response to your other statement, I mean it acted as a normal, healthy computer would. It didn't simply beep a couple of times. The power seemed to flow as it would in a health computer when everything was hooked into the tester. Does that make any sense? I'm not sure I'm saying this right.

 

[C6Gunner]

The MB may be shorting out on the case. Take it out and test it.

Also, did you test the CPU?


S.

 

[NYJimbo]

Is your PSU tester a LCD or LED model?.

While it may be the mobo, its too early to tell without any real diags.

I hate to be a bitch but have you tested a machine at this level before?. If you can get your hands on a POST card see what code it ends with.

Reseating is nice, but did you REMOVE things and then test ?

 

[studiot]

Can't visualise your psu tester.

 

[ComputerClinic]

Hey, guys. I have what is probably going to be viewed as a dumb question. Certainly a newbie question if nothing else. I am working on a computer that I originally thought had a bad power supply. Basically, it wouldn't turn on. You could plug in the cord and there would be a click, the PS fan would very lightly blow briefly (maybe for half a second), another click and then there would be absolutely no activity. I got my power supply tester and ran a diagnostic. When I plugged everything in, it registered everything as normal and the computer stayed on like any other system would (obviously there was no display or processing as the motherboard had all but been taken out of the situation). My question is this: This sounds like the motherboard needs to be replaced, right? Is there anything else I can test first? Any input? This would be my first OTJ experience replacing a motherboard is the only reason I ask. What else could be wrong? I have also reseated virtually every piece of hardware in the box as a last-ditch sign of desperation. I am drawing a blank...

Thank you for any input you provide.

I'm a little confused. You tested the PSU with a PSU tester? I would try a different PSU because PSU testers aren't always completely accurate. If after swapping the PSU you find that the problem is still there, remove every add on card and front bay device (HDD, optical drive, etc) and it will either work or still have problems.

The computer works after removing devices: replace each device one by one testing after each device until you discover the specific device causing the problem.

The computer still won't work after removing devices: replace memory with known working memory and try it in each slot. If its not a memory problem, take the heatsink off the CPU and check for possible heat damage. If the CPU seems fine, its very likely the motherboard because CPUs RARELY fail for reasons besides overheating.

Edit: As a final step, remove the motherboard from the case entirely and see if it will POST with just the mobo, processor, and known working RAM.

 

[studiot]

I still don't understand what you are saying.

If you had the psu connected to a psu tester, how did the computer manage to start?

The original symptom you describe is consistent with a fault being detected very early on in POST. The keyboard check comes almost at the beginning in Dell BIOS.

So the pc starts, but quickly finds a fault (eg a shorted usb or keyboard etc) and shuts down again.

Incidentally although the 8400 is an old model it is new enough that the psu has a conventional power wiring. Olders Dells ( and Compaqs) may not.

 

[drewm]

Thanks for you help, all. I guess I am not very good at explaining what is going on in this situation. My apologies. I'll get it. I just need to put on my big-boy pants and see what I can do. I have a POST diag card on order, so that should help me some. Thank you for all your comments. Again, I'm sorry.

 

[Skyhooker]

I'm still not clear on the symptoms. Are you saying that the computer doesn't run after you connect everything and press the start button, or is the problem you're describing only that brief spin-up of the power supply fan and the LEDs that come on at that time? If only the latter, and the computer actually runs normally when you then press the start button, I believe that's just the normal self-test that the Dell power supplies themselves run when connected to power (at least the older ones).

Sorry, but I just couldn't find where you said it simply wouldn't run at all (apologies if you did - it's early and the coffee's still kicking in ).

 

[gazza]

Hey DrewM,

I would try turning off your computer disconnecting the power cord and taking the cmos battery out of the motherboard for 10 minutes then replace it and restart the computer.

 

[PcTek9]

1.) does windows ever come on the screen ?


Do keep in mind that some post cards can help you differentiate between a dead cpu and a dead motherboard.
Some post cards have like 8 LED's in adittion to the numeric led's, and the 8 LED's represent among other things,
if it is the cpu or the motherboard that is dead. (something that can be very hard to tell if you dont have a known working cpu for every model of cpu laying around...)

 

[atlanticjim]

So the pc starts, but quickly finds a fault (eg a shorted usb or keyboard etc) and shuts down again.

1+ I have had this problem now twice on a Dell Mobo. One was a trashed USB next to the switches (plugged into the mobo) and the other was one of the USB on the Mobo back panel itself. In the end an easy fix (and in my diag list).