820-4652 imac dont turn on

Dozer

Member
hi, i am just workin g on this device, no problems to see on the board

first green led is lightning, no reaction by pressing power button

pwr_btn_l ckecked

platform reset is still low

i have 3.41V, 3.3V_s0 and 5V s0 and 12V_S0

I dont have PP5V_S4_REG

PP3V?V_S5_REG is ok

both enable Signals on 7600 are there

replaced already u7600, but no change, checked R7656, R7603, R7650, R7672, R7670, R7671, R7659, R7650 all ok


checked q7650 and q7655 in diode mode, nothing to find

no short on L7650 to GND

what else could be the problem in the imac?
 

Dozer

Member
yes, that was for me the intresting part as well.

now i checked again and yes there is no 5V_S0, but I replaced already U7600 inbetween

so I measured bad S4 or bad S5 and have now a bad U7600. I am gonna replace it again and will post the measurements after that.
 

Dozer

Member
I checked now again

PP3V3_S0 is ok

there is no PP5V-S4_REG
U7600 and Q7650 and Q7655 are replaced already
PM_EN_REG_P5V_S4_R (EN2) is 3.3V

it is lighning only the first led from the mainboard
 

2informaticos

Administrator
Staff member
So 5V_S4 is enabled, but not present, check why.

Did you solder new ISL62383C?
Check the solders, R/C7656 and al other surrounding components, related with 5V_S4.
Be sure no short to ground, nor low value at L7650.
 
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