South Bridge is also called ICH or input-output controller HUB. System will be dead if there is any fault in South Bridge. In this post I will explain how to confirm that south bridge or ICH is faulty in a desktop motherboard step by step.
Check impedance in A14 pin of PCI slot.(Side of PCI slot towards processor is called “A” side). 3.3 Standby voltage comes to A14 pin of pci slot. If the impedance is less than 80 ohm, that indicates that south bridge is faulty.
Check the impedance of capacitors near the south bridge.Put the multimeter in continuity checking mode. Place black probe to the positive pin of the capacitor and red probe to ground. If the shown value is less than 200 ohm, we can assume that south bridge is faulty.
Check the impedance at the middle pin of CMOS clear jumper. If it gives very less impedance of multimeter produces beep, that indicates that south bridge is faulty.
Check impedance of the following pins of IDE port. If multimeter gives beeps, that means south bridge is faulty.
If ICH/South Bridge Heats after connecting SMPS ( before pressing ON button) that means it is heating by stand by voltage. In conclusion we can assume that south bridge is faulty. If ICH produces excess heat after power on that also concludes that it is faulty.
If south Bridge is in good condition will generate PLT Reset signal (3.3v). Check for this signal at PCI slot pin A15.