In fact on my iMac Intel 17" logicboard there's only have 12 pins. I guess 20" needs INV_CPU_HI and LCD_PWM but 17" doesn't. PP12V_ALL ALL for "always" on. PP12V_RUN RUN for when PSU is on. But PP12V_ALL and PP3V3_ALL can't be provided by an ATX PSU (there is only the PP5V_ALL) PS_ON | PG 12V | GND 12V | 12V 5VSB | GND GND | 5V 3.3V | 3.3V doesn't work !

Hi, I guess SYS_POWERUP_L_BUF may be the ATX PS_ON ! Did you find more clue ? I have an Intel iMac LogicBoard and i would like to bring it back to life too ! Thanks