Author, check the resistance of ceramic capacitors (both present & absent) around the South Bridge. If one or more of them like short (<1 Ohm), then
1) It's Pulse (typically PWM) stabilisator output. May be shorten lower side MOSFET or diode, or controller.
2) (Most cases) - SB failed.
If there's linear stabilisator like 1117, 1084 which supplies SB in standby, and it's hot, and in standby SB is not cold, in most cases SB failed.
Author, check the resistance of ceramic capacitors (both present & absent) around the South Bridge. If one or more of them like short (<1 Ohm), then
1) It's Pulse (typically PWM) stabilisator output. May be shorten lower side MOSFET or diode, or controller.
2) (Most cases) - SB failed.
If there's linear stabilisator like 1117, 1084 which supplies SB in standby, and it's hot, and in standby SB is not cold, in most cases SB failed.