Here is my modest contribution to your knowlidge base about southbridge problems and using metod "отжига" :)

ASUS P4P8X SE come with big hole on the center of  "юм" but Motherboard did turn on and POST was D0. I measured USB for short`s on Null and I found that "юм" already "отжeг" himself. All I need to do is to find hese voltage supply and here it is:

VCCSUS1_5A = capacitor that is not marked and it`s located between c29 and r234

VCCSUS1_5B = capacitor that is not marked and it`s located between numbers 4 and 5

VCCSUS1_5C = capacitor that is not marked and it`s located between r234 and c35

Only VCCSUS1_5A was defect and had 0.18V. 

I put resistor vith low resistance between VCCSUS1_5C and VCCSUS1_5A because they are very close but have to be careful not to make shorcut with r234.

After that, POST card start to sent proper codes. Only you must put active cooling on "юм" and PCI USB card.