[MoBo] High load on +5VSB power connector

[sarouiki]

Hi guys,
it's my first post on this forum! I would like to attend the discussions since I think they are very interesting!

I got a problem with my MoBo Asus P5L-1394 (Socket775): the MoBo won't start when I press the switch-on button on the front of the PC.
I have already made the following trouble-shooting actions:

1. the power-on switch of the box works correctly (I also tried to switch on the PC by shorting PINs on the MoBo)
2. I removed the MoBo from the the box and tested it on the cardholder (in order to avoid any shortening on the backside)
3. I removed all the components leaving only CPU and RAM: nothing changed; the MoBo won't start
4. the stand-by green LED on the MoBo works correctly when the PSU is connected and the power-cord is connected to the power-let into the wall. Something strange: the front-panel power led is light-up even if the MoBo is in stand-by (it should be off)
5. the PSU has 2 bad caps related to +5VSB rail. I have recapped them and now the PSU works correctly on another working PC (thanks to this forum for the suggestions about recapping). I think these caps have been broken because of a too high current drain from the MoBo
6. the +5VSB rail of the PSU provides +5V when it is not connected to the MoBo Asus P5L-1394 whilst it provides +3V when it is connected. When connected to the working PC, it provides +5V, so I think the problem could be the Asus MoBo
7. I have connected a +5V power source from a regulated power supply (10 Amp max) between +5VSB and ground of the power connector on the MoBo in order to measure the amount of current drained by the MoBo: the result has been: about 3 Amps!!!!! I seems to be too much since no USB peripherals are powered by the MoBo!!!! I have noted that the South-Bridge IC (installed on the lower part of the MoBo) is getting very hot in few seconds so it could be the cause of the current drain. This too high current drain could be the cause of the +5VSB voltage drop and PC won't powering on!!!!

Now the question is: what can I do? All the caps seems to be OK on the MoBo! Do u think the MoBo is garbage or I can try to do something to recover it? What can I do further?

The PSU under test is a Thermaltake TruePower 430W!

Thank u very much for your suggestions!
Bests

SaRo

[kc8adu]

Re: [MoBo] High load on +5VSB power connector

look for a busted usb port.
many run from +5stby to support power on by keyboard/mouse.
they often short when broken.
boards that get zapped through the onboard nic often overload the +5stby too.
i have desoldered many a damaged nic chip to get these working.

[sarouiki]

Re: [MoBo] High load on +5VSB power connector

Hi,
thank u very much for the answer!
Do u think that the heating of SouthBridge could be related to a USB short or NIC short?
How can I identify busted USB ports of NIC?
Thanks in advance
Bye

[kc8adu]

Re: [MoBo] High load on +5VSB power connector

southbridge heating can mean its damaged.can you hold your finger on it?

[sarouiki]

Re: [MoBo] High load on +5VSB power connector

I have removed the heatsink from the SB IC in order to put the finger directly on the IC. When I connect the PSU, the SB IC becomes very very hot after some seconds. I can't keep the finger on it because it is too hot.
Is it a symptom of bad SB IC? I think yes but I would not!

Do you think that the research of the bad parts of the MoBo could be considered finished and I have to consider it as garbage?

Thanks

[kc8adu]

Re: [MoBo] High load on +5VSB power connector

its gone.