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Imac 21.5 - 820 3588 - Some times turn on some times not

N

Noguinfor

New member
Hey guys,

Working on imac 21.5 - 820 3588. this one came with the problem not turning one.

I open it, removed the board and i noticed that cmos 3V was only with 1.5V.

I replace the pile for a new one and i thought the problem was solved but after 2 days the problem remains!

I already clean_me the original bios tried a new one but no changes!

I already try to shunt the pads directly on board no changes to!

If i remove and insert the cmos the machine works normal but after 1/2 days stop turning one! This machine is very unstable. Some times turn on some times not!

already try to start in SMC bypass don't turn one to!



has anyone had any similar problem??
 
N

Noguinfor

New member
Already check signals and seems ok! CMOS remains at 3V. I


I already did a reflow on SMC, jump a wire directly J5120 (SMC_ON_OFF) to J6901 (PWR_BTN_R) and same history the machine don't turn on when button is pressed!

I've been fixing some old imacs with the similar problem replacing LTC3851. Can this problem be something like that?

thanks
 
N

Noguinfor

New member
with my power supply connected to the board and when it don't turn on, the power supply consume 0.070A and i have this signals:

PP3V42_G3H = 3.4V
PP5V_S5 = 5.1V
PP3V3_S5 = 3.3V
PP5V_S4 = 5.1V
PP3V3_S4 = 3.3V
PP3V3_S4_AP = 3.3V
PP3V3_ENET = 3.3V
PPVDDQ_S3_DDR = 1.3V
PP5V_S0 = 5.1V
PP3V3_S0 = 3.3V
PPVDDQ_S0 = 1.3V
PPVDDQ_S0_CPU = 1.3V
PP1V5_S0 = 1.5V
PPDDRVTT_S0 = 0V
PP1V05_S0 = 1.05V
PPCPUVCC_S0_CPU = 0V

when the machine remembered to turn on, the power supply consume only 0.010V

and only have this signals:

PP3V42_G3H = 3.4V
PP5V_S5 = 5.1V
PP3V3_S5 = 3.3V

weird problem!
 
2informaticos

2informaticos

Administrator
Staff member
Don't confuse turned on with working state.
You board turns always on, as you get even S0 voltages.
Missing CPU VCORE for some reason.
Resolder U7000 and U7110/30/50 areas.

Be aware, this board uses the f***g FDMF6808 chips.
You can try changing all with NEW FDMF6708.
 
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