dead computer

R

rustickjohn

Geek Trainee
HI

Would appreciate any comments please...

emachines 3220
2.8Ghz
512MB RAM

A few days ago my daughters computer decided to play dead, it was working perfectly OK the night before when she turned it off, but when you press the power button, absolutely nothing happens... no lights, no fans, nothing on the monitor, nothing...

When you open up the case, the only sign of any life is a green light on the motherboard...

What I've checked\done ...

1. I immediately guessed at the psu & replaced it ... wrong ... no difference..

2. Start button am I mcorrect... When you click the start button, this should set the startup process in motion by causing something on the motherboard to reduce the voltage of the green wire from 5v to under 0.8v thereby causing the power supply unit to spring into life... ?

I've taken the start button out of the process by directly shorting the pins on the motherboard ... no effect

No Monitor or hard drive activity, no led's lit ...

I tried with the power disconnected from the harddrive, floppy, CDRom drive & DVD drive ... still nothing, & with the RAM removed ... just in case something was dragging the power down ...nothing

Also removed the modem card...

The Start button has 3.23v going through it ... & a continuity test shows the start button is working..

When I short the green & Black in the 20 pin connector ... the values in the molex connectors are :-

red to black 5.24v

yellow to black 12.22v

But still NO LED's show on the case & the Harddrive does not fire up...

I have put the harddrive in another computer and it tries to boot (blue screen error - a recent change in hardware etc,) which is to be expected as it is a different computer ... still using the other computer, I am able to boot into knoppix from CD & access all the files on the drive.

3. I have removed & reseated the processor .. which looks fine... no signs of heat...

4. The motherboard also shows no sign of damage (power surge) NO melted caps etc,

I am now 99% certain that it is a dead motherboard would you agree ? is there anything else I can do to make that 100% sure, before getting a new motherboard ?


Thanks in advance...
 
Try an ATX Reset - Remove power cable and peripherals, hold power button down for about 30 seconds, release it, plug power cable in only, and try to start it up... If this still doesn't work, it's a dead mobo.
 
rustick said:
I immediately guessed at the psu & replaced it ... wrong ... no difference
Click to expand...
what is the make & model of the new PSU you put in ?

BTW: emachines were well known to have "crappy" PSU's
 
Thank you for your replies NeloForster & donkey42

NeloForster...

I will try what you suggest and let you know...

donkey42...

The original PSU was a 250watt which I replaced with a Sumvision model KY2000ATX 350W P4

I think the relevant point is (well this is the part i don't understand)...

1. pressing the power button does NOT make the computer boot ... no led's, fans, drives nothing

BUT

2. shorting the green\black wires, DOES cause the PSU to fire up, and fans to start running & does supply a 12v & 5v to the molex connector (to hard drive) ... but no led's, & harddrive does NOT spin up, even though it has power ... however the harddrive DOES work in another computer.
 
rustick said:
Sumvision
Click to expand...
personally i've never heard of Sumvision however after doing a quick net search, i discovered: Sumvision PSU's are not good, a good quality brand of PSU (300W) can supply more power than some crappy generic 500W PSU, it's not about wattage, the output wattage of a PSU does drop over time
rustick said:
shorting the green\black wires, DOES cause the PSU to fire up
Click to expand...
strange, exactly which green & black wires

Edit: you may wish to check out B's PSU Sticky for a list of decent PSU brands
 
donkey42 said:
strange, exactly which green & black wires
Click to expand...


Pin 14 (green) on the 20 pin connector to any black (ground) wire ...

ATX Power Supply Wiring

The 3v which is present at the power switch (when pressed) returns the 3v to the motherboard, this causes the voltage of the green wire (pin 14) to be dropped to less than 0.8v .. at which point the PSU springs into action...

Only with me it doesn't ... & even when I bypass the power switch, to power up the PSU, only the fans work, nothing connected to the IDE cables or floppy cable work, even though they have voltage...

Thanks for the ongoing comments... :)
 
rustick said:
The 3v which is present at the power switch (when pressed) returns the 3v to the motherboard, this causes the voltage of the green wire (pin 14) to be dropped to less than 0.8v .. at which point the PSU springs into action
Click to expand...
yeah

rustick said:
Only with me it doesn't ... & even when I bypass the power switch, to power up the PSU, only the fans work, nothing connected to the IDE cables or floppy cable work, even though they have voltage...
Click to expand...
is the 20 pin connector attached to the mobo, or are you firing up the PSU without attaching it to the mobo
 
Try Barebones Method...

Take out the Mobo out of the Case and leave it with only,
CPU
1xHDD
1xRAM
1xVideo Card(If onboard is not available)

Short the Mobo pins with a flat screen screwdriver and see if it works..

Also as Dave(Donkey) suggested, you might better off buying a good quality PSU because a generic PSU can cause damage to your whole system and also it gives lot of problems of automatically system restart nd all...
 
Please let's have a little respect here :( ... do I sound like a complete newbie ?

If the 20 pin connector was not connected to the mobo, then where would the 3v at the power switch be coming from ?

& how would the green wire (pin 14) sense when the voltage had dropped, in order to fire up ?

Also I think most people with any knowledge of PSU's knows that to fire one up without a load is the quickest way to fry it.

AS I am trying to get the computer to boot, what would I possibly gain by not having the 20 pin connector connected to the mobo ?
 
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