820-01061 imac dont turns on, but if 2xclick power button quick is ok

Dozer

Member
Hi, got this imac with now signs of life, no led nothing, replaced with a known good power unit, nothing.

found short in PP12V_ACDC pin 3 and 4 J6900
figured out, that Q8450 is blown, replaced it and the short is gone
now already the first LED is coming up but after pressing power the LED turns off

so i checked the board again and found another short in the PP12V_S0_REG_CPUCORE_F line
figured out the cap C7225 is blown, replaced it and all now all 4 leds are coming up and the dong

but the intresting thing now

by pressing powerbutton the first led is turning off and after a second turning on again, nothing more happens
by pressing it again same procedure

but by pressing the powerbutton more quick 2 times (first time led off and in this moment second time) then the mainboard starts like it should be, till the 4th led and the gong


but i cant say my customer that he have now press 2 times and quick to turn it on.

i have no idea what can be this ?
the power unit i have 3 and all 3 is the same problem, so i think should be on the mainboard still. need help please
 

Dozer

Member
tryed PRAM reset, but not better.

it only turns on if i press the power button within 2 seconds 2 times. after 3 seconds the first led turns off and on again
 

Dozer

Member
i dont can say anything about PM_PWRBTN_L and PM_SLP_S4/3 measuring during press PowerButton because
PM_PWRBTN_L
 
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