ASUS K8N will turn on for 2 seconds then turn off

[Dan81]

As the title says,I have an Asus K8N (nForce 3 250 chipset) that powers on for 2 seconds and then turns off. It also turns on 1 second after I plug the PSU AC cord.

Here's what I did:

Remove CPU - same thing
Remove RAM and install speaker - same thing except it BEEPS for RAM (AMI BIOS)
Remove AGP GPU (FX 5200 128MB) - same thing as the main problem
Remove 12v P4 plug - only a fan twitch then nothing

I've tried 4 power supplies I've had around:
Premier LC-C400ATX (recapped with Chemicon caps)
Delux ATX-450W P4 (iMicro clone)
Rexpower PX-400 (recapped)
Sumvision KY-450ATX 350W (recapped with Nichicon and Rubycon caps)

Neither of them changed anything. Each one I tried,they all did the same - turn on for 2 seconds (CPU fan spins up) and then turn off. They all work fine on other systems however.

Any ideas? The fact that if I remove RAM it beeps makes me believe it's salvageable.

PS:After it turns off,I can't even turn it back on until I unplug it from the mains (Premier LC-C400ATX) or flip the rocker switch (Rexpower,Delux and Sumvision). Oh,and the motherboard itself uses Panasonic FJ caps only.

[stj]

Re: ASUS K8N will turn on for 2 seconds then turn off

if you have the equipment, reflash the bios first.

[reaper57]

Re: ASUS K8N will turn on for 2 seconds then turn off

Do you have a spare mb with the same socket to test the cpu? What I am think is one of the components, cpu, ram, gpu might have shorted something on the mb causing it not to post.

[c_hegge]

Re: ASUS K8N will turn on for 2 seconds then turn off

It does have an Nvidia bumpgate chipset. That might be the issue too.

[Dan81]

Re: ASUS K8N will turn on for 2 seconds then turn off

It does have an Nvidia bumpgate chipset. That might be the issue too.

It's a nForce 3 250 chipset. Also,it's still working somehow.(again the fact that it beeps for RAM makes me think that)

reaper57 - The board beeps if I don't have ram and have anything else (CPU and GPU and the HSF) Also,all components tested good,especially the CPU and the GPU.

stj - Reflashing didn't help. It does the same,EVEN without the BIOS chip. So this eliminates the BIOS,especially since it reacts to no RAM by beeping

[stj]

Re: ASUS K8N will turn on for 2 seconds then turn off

well if it beeps then the cpu is running so it may be shutting down for safety.
if your sure the psu is good, the first things i'd try are the battery and a different cpu fan incase the current one has a faulty tacho output making the board think it's not running.

[shada]

Re: ASUS K8N will turn on for 2 seconds then turn off

reflow chipset

[shada]

Re: ASUS K8N will turn on for 2 seconds then turn off

it will 100 percent

[c_hegge]

Re: ASUS K8N will turn on for 2 seconds then turn off

It's a nForce 3 250 chipset. Also,it's still working somehow.(again the fact that it beeps for RAM makes me think that)

That means nothing. The memory controller part of the chipset might be OK, but that doesn't mean the rest of it is. Reflowing or reballing is only a temporary fix at best on those. The chipset really needs to be replaced if you don't want the issue back again.

[Dan81]

Re: ASUS K8N will turn on for 2 seconds then turn off

That means nothing. The memory controller part of the chipset might be OK, but that doesn't mean the rest of it is. Reflowing or reballing is only a temporary fix at best on those. The chipset really needs to be replaced if you don't want the issue back again.

I'd give my two cents and say that it would be the voltage regulator the culprit but I'm not sure about that. Also another 2 cents,
If it would be bad,wouldn't it get insanely hot in those 2 seconds?

Another info that might help - I once tried to jump the green and black wires so I could keep it running instead of shutting down,and strangely it beeped once which meant that it did POST,and the LCD led lit green,but it lost signal. I couldn't get it to do that again.

BTW,I have no tools for reflowing/reballing.

[Agent24]

Re: ASUS K8N will turn on for 2 seconds then turn off

BGA soldering issues don't cause chips to overheat. They just cause them to not work...

[c_hegge]

Re: ASUS K8N will turn on for 2 seconds then turn off

^
Yup. If something gets hot very quickly, it means that there is a short. The bumpgate issue just cracks the chip's internal soldering, causing parts to become disconnected. It does NOT cause it to get hot.

[TractorGear]

Re: ASUS K8N will turn on for 2 seconds then turn off

I see those symptoms when I forget to plug-in the extra, 4-pin supplemental power connector to the motherboard. Forget what it's called. Fans "lurch", then shutdown. I agree with OP's reasoning. If it complains about the absence of RAM, then the problem might not be catastrophic. SOMETHING is working in there. Only thing I could suggest is to give the motherboard a VERY close inspection top & bottom and look for signs of overheating, etc...

[momaka]

Re: ASUS K8N will turn on for 2 seconds then turn off

PS:After it turns off,I can't even turn it back on until I unplug it from the mains (Premier LC-C400ATX) or flip the rocker switch (Rexpower,Delux and Sumvision). Oh,and the motherboard itself uses Panasonic FJ caps only.

That alone sounds like a short-circuit on the motherboard somewhere. My best guess would be a MOSFET, linear regulator, or perhaps audio/LAN chip (i.e. something the board does not need in order to boot).

*However*
The fact that the motherboard remains ON when you "manually" force it ON by shorting the PS_ON wire to ground, tells me there may be something else going on.
(lol, I think I used too many "on"s in that sentence )

This being an ASUS, maybe your board could have that "Chassis Intrusion" error seen here:
https://www.badcaps.net/forum/showthread.php?t=32502

Other things I can think of: shorted pins in a USB port or shorted 5V line in VGA connector (if your board has one)? The former I have seen for a motherboard sold on eBay. Seller described it as "boots, but says 'USB port over-current'" after which the board shuts down. He even showed pictures of that. And it was an ASUS motherboard also (socket 939 IIRC, so not much newer than what you have).

[Agent24]

Re: ASUS K8N will turn on for 2 seconds then turn off

Or some voltage rail is dead, or perhaps there is some critical logic signal missing (like CPU VID signal to the VRM controller) and it just shuts off after waiting 2 seconds.

(Intense speculation on my part, I don't think a shutdown would be normal for this situation, but then Asus likes to do weird shit...)