Question New PSU on LGA 775 MB only starts with 4-pin CPU connector unplugged ?

Nov 23, 2022
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I'm in the process of building a retro gaming rig:

ASRock 4CoreDual-VSTA LGA775

QX6800 Core2 Quad Extreme 2.93GHz

2x1GB OCZ Dual Ch. DDR2 6400 667MHz

Gigabyte Radeon HD 4650 1GB AGP

128GB SATAIII Samsung SDD

Evga 750w G3 Modular PSU


Everything works fine with an old generic 400w PSU w/ 20-pin ATX & 4-pin CPU. But a modern EVGA 750w G3 will only start with the 4-pin CPU connector unplugged.
The evga works fine on my 2700x, 1080ti (x2) system. And no short to ground detected on the +12v rail of the 4-pin CPU connector (MB, CPU cable, & PSU).