820-00292 iMac 27-inch 2015 only 2 LED lights , Fan spins No chime.

[Mac Repairs]

HI all,

This board has only 2 led light up no chime. Tried different rams no luck.
All the power rails are present . cpu 12v FET gets 12 v. How ever Q8450 pin 4 FET_EN_P12V_S0_R is 24v. I dont kno is this correct volatge .

I have 2 logic boards same model same issue.

Any help greatly appriciate .

 

[2informaticos]

"I dont kno is this correct volatge"
It is...

VCORE present?
Check PLT_RESET_L too.

Did you test USB activity?

Try known good BIOS, just in case.

 

[Mac Repairs]

Hi 2 info thank you for your reply. PLT_RESET_L is 3.3V, PPVCC_S0_CPU is 1.2V. PPVCCGT_S0_CPU is 0v.

NO USB Activity. I'll try with good known bios, could this be bad CPU? I have 2 boards one with i5, and i7 6700k . I swap the CPU's still the same.