*SOLVED*IMAC A1418 2014 820-4668 not booting

[donnos]

Hello,

I have a 820-4668 not booting, after a few measurements, don't see obvious short or any heating.
I have the 1st LED but when pressing power botton has no reaction.

my confusion is that in no_boot state i have S5 state power rails(which i do have). but the board is pushing out PM_SLP_S5_L(3.3v) which is S4 enable before power button is pressed, Is this normal?
i have pp3v3_s4 but no pp5v0_s4. should i start my troubleshooting here? pin 24 of U7600 is 3.1v but no pp5v0_s4 output

 

[2informaticos]

"i have pp3v3_s4 ... but no 3v3_s4 output"
What we should understand there???

The board must start by itself when power is connected.
However, if stuck in S5, you can trigger SMC_ONOFF_L and check for reaction at PM_SLP_S4/3_L signals.

12V_S0_FET pulse at least at the same time?
Q8450 is a common failure in these boards.

 

[donnos]

typo there i i have pp3v3_s4 but no pp5v0_s4 even when pin 24 of u7600 is enabled.

SMC_ONOFF_L can be triggered when power button is pressed.

so seems i'm going past s5 state. i have PM_SLP_s4 and S3.

12v s0 is constant ON @12V, not pulsing.

 

[2informaticos]

PM_SLP_S3_L stays high?
Then various S0 voltages should be present.

Post diode mode to ground at 5V_S4 (L7650).

 

[donnos]

Yes some of the s0 power rails are running except for those depending on the 5v rail.

Diode mode reading is 0.165 done at L7650

 

[2informaticos]

Then change U7600 and check all surrounding components and solders.
Pay atention to R/C7656.

 

[donnos]

Changed U7600 to resolve issue. Thank you for the guidance