[SOLVED] 820-2784 iMac A1311 don't power on

[rzeszu]

Hi,
I have Apple iMac A1311 K74 MLB 051-8337 820-2784 for repair with no power.
After i plug in PSU i get LED1 green for 1 second and thats all.
I checked U7700 and P3V3S5_12VE_EN1 is 3,8V
I soldered new U7700 without any success, still no P3V3S5.
I have only 12Volst on board.

Could You help me with this problem, maybe i looking for problem in bad place.
This is my first iMac board for repair.

Kindly regards Mariusz

 

[Repairable]

First measure more power rails and report them all here see if one is missing or of on the volts it Should be

 

[rzeszu]

PP5V_S5 4.99
PP3V3_S5_REG 0 (only 3.3V after plug in for 1sec)
PP12V_S5_fet 12V
PP3V42_G3H 3.41V
PP12V_G3H 12V

What else i could measure?

 

[dukefawks]

Probably a short on one of the S3 or S0 rails. Measure all voltage rails for shorts.

 

[rzeszu]

You were right, it was PP3V3_S3_USB_HUB line

When I put 3.3V at PP3V3_S3 line nothing was heating but after 1 minute short disappeared and i find this place.
Thanks for the answers.
Mariusz

 

[dukefawks]

So this one is solved now?

 

[rzeszu]

Yes, thanks.
iMac works perfect.