Dead Motherboard?

[LuckyTxGuy]

Ok, time for me to ask a question.

I've got a customer/friend's E-machine desktop here and it's a freebie job so I don't want to spend forever fixing it. The friend is older and knows little about computers. They said one evening when they booted it the keyboard wouldn't work and everything seemed really really sluggish. Then the mouse wouldn't work, but they got XP shutdown. (pulled the plug?) Anyway, next day it's dead. Nada. Won't power on at all.

Enter: Me. I bring it to my office plug in a power cord and hear a quiet but high pitched squeal from the PSU and the machine is dead. No lights, no fans, NOTHING. I assume it's a bad PSU. My PSU tester shows that the PSU is putting out too much power, it doesn't give me an exact reading but the code translates to too much power. I put in a brand new working PSU thinking that is it and to my surprise, nothing. Dead.

Then I'm thinking it's the power switch. I used my meter to determine the switch is in fact working. Odd. This thing is just flat dead.

Any thoughts? I've almost convinced myself it has to be the motherboard. What do ya'll think?

[buckslayer80]

Hmmmmmmmmm.

Well if we think about the order of a PC's power up cycle in order, you solved the first 2 stages. Do the fans or anything come on now? Even with a dead MB the primary fan on the PS should still spin if its getting power, right? Everything that's directly connected to the PS should power on if its not dead.

Do you have an Experts Exchange account? Being in the biz it's the best $25 you'll ever spend. I'll post it on there for you. They usually respond pretty fast. I'll post what the big boys have to say.

[SamIAm]

If the motherboard dies, it can take other stuff with it, right? When my PSU died, it emitted a high-pitched squeal, and took the motherboard along for the ride.

[ QUOTE ]
Everything that's directly connected to the PS should power on if its not dead.

[/ QUOTE ]
Keep in mind that the PSU doesn't send power to the fans all the time, but only when the rest of the computer's on. Since only the motherboard knows whether the computer's set to "on", but the PSU gets power from the wall all the time, the PSU must listen for the mobo to know whether to send juice to the fans. This means there are dead motherboards that cause the PSU to not activate the fans.

Am I off base here? I'm making this up as I go along.
-Sam

[LuckyTxGuy]

Thanks for the replies guys.

Buck, I thought EE was about $100 a year? Either way, I need to join up I've just been too lazy. Their site is always the first search result when I google error messages and such. Glad to hear it's worth it, I'll look into it.

When I say this thing is dead....I mean dead. With the new PSU still installed and the power cord plugged in, absolutely nothing at all happens. I'm talking nothing. Nothing spins, no lights, nada. However......when I plug in my digital PSU tester, the PSU fan starts to run very quietly as the PSU powers up. So this leads me to believe the PSU doesn't even know it's plugged into the motherboard, ie: the mobo is dead. (?)

Sam what you are saying about powering up fans etc, makes sense to me too. Whether it's right or not, I don't know. [img]/images/graemlins/smile.gif[/img] Sure sounds good though.lol

I can't stress enough that even with the new PSU installed, everything (including the PSU) acts dead as a door nail, until I plug in my PSU tester and then the PSU comes to life.

What I wondered was if the high voltage that my tester is showing on the old PSU didn't take out the motherboard and who knows what else?

Thanks for the help. The problem is if this thing is toast, and it's not worth spending much $$ on, it's going to be hard to explain to these (older) folks that their computer just "died".

[DQPaulie]

Some eMachines had PSUs that would kill the motherboards ( google it ). Happen to my friend, had to buy an overpriced motherboard from emachines, which they supplied a PSU with for free. They would make you call before placing the order, and they told you to make sure you did not use the original PSU. I went through them for this motherboard because it was oem windows, and I wasn't sure I could reinstall without the same motherboard at the time.

Paulie

[buckslayer80]

"Some eMachines had PSUs that would kill the motherboards"

Well this is what they think too. I'll post their responses. Beat: eMachines

Unfortunately, a bad PSU can damage whatever is connected to it, so now you have a possible dead motherboard or hard drives or video card (if it was plugged into the power supply). E-machines is not exactly the brand that comes to mind when thinking of reliable hardware, either.

So we definitely have a bad psu and it looks like it took out the motherboard, its very likely other hardware was also damaged. I have seen bad power supplies especially ones with over voltage issues take out multiple pieces of hardware(cpu, video card, hard drive, etc). Is the system still under warranty? If not you could replace the motherboard but there is a good chance other hardware was fried. For a much as it may end up costing in the end they may just want to get a new system.

what do you mean? too high voltage? that can and will damage the connected components.
i would start by testing all components on a good working PC first : new PSU, disk, ram, cd drive, PCI and video cards, etc . . even CPU if possible.
then start with the good devices, with a minimum :
mobo+cpu+1 ram stick, video card and PSU --> any display?if not : one of the connected is bad; try swapping ram, video card, psu

ps - if you want to test the old PSU, use a V-meter to check the outputs first; look here for how to :
http://www.fonerbooks.com/power.htm
http://www.duxcw.com/faq/ps/ps4.htm

Ouch - sounds like a dead mainboard too. Did you notice any cap leakage or physically blown capacitors around the ATX connector or CPU socket? I have experienced many faulty PSU's and generally I notice a physical sign with regard to too much juice being pumped out of the unit. Either as I mentioned, blown or leaking capacitors or if it goes further than mainboard - check the IC's on the HDD board etc.

Out of interest - does the new PSU that you fitted work on another board? When you checked the power switch (assuming you meant from mainboard header not PSU rocker) - did you disconnect and manually 'jump' the pins?

[LuckyTxGuy]

I'm tied up today but I'll post back this evening. Thanks for the info fellas.

I will add that this E-machine is several years old by no means worth spending more than $50-$100 max on. If it were mine, I wouldn't spend that much.