820-01700 PP3V3_G3H_T missing

[JdYoda]

Hello.

Mac A2141 doesn't turns on. 20v 0.05A with battery, 5v 0.05A without battery.
Found short on PP3V3_G3H_SOCPMU (C7805), after i changed cap - short is gone.
Now PPBUS - 12.3v,
PP3V3_G3H_RTC_X - 3.3v
PP3V3_G3H_T - 0.4v
Other voltages are missing, so no DFU as well. With R5750 removed - PP3V3_G3H_T is 0v and PP3V3_G3H_SOCPMU is 1,5v
PP3V3_G3H_T comes from U7650, but there are no enable signals for this chip, P5V_3V3G3H_EN comes from PMU_PVDDMAIN_EN, and it comes from U7800. Changed U7800, no changes.
Schematic shows there are 3 LDO_IN for U7800: PP1V1_SLPS2R (missing) PP1V8_SLPS2R (missing) and only PP3V3_G3H_RTC_X is present. So as i understand U7800 is not powered and not creating voltage for T2
Im not sure which chip is responsible for creating SLPS2R signals, is it U7800? Looks like im stuck here...
Thanks for help in advance!

 

[2informaticos]

"there are 3 LDO_IN for U7800: PP1V1_SLPS2R (missing) PP1V8_SLPS2R (missing) and only PP3V3_G3H_RTC_X is present. So as i understand U7800 is not powered"
Wrong understood!
LDO_IN are the points where PMU connects to LDO0-3 outputs to supervise them.
PMU generate these 3 LDO-3 voltages, powered from PP3V3_G3H_RTC_X , through R7900; did you check if the resistor is good?
LDO_RTC and VOUT_RTC must appear at same time.

Check for short at all U7800 surrounding coils, L78xx.

 

[JdYoda]

You right, R7900 was blown, 350k. There was only 1,5V on second pin. Now laptop works. Thank you so much! Really appreciate your help!
So there was no power for U7800, is it correct?

 

[2informaticos]

Exactly!
You've went for hard job first, changing U7800.
Possibly was bad, if R7900 found open; but very easy to check with a diode mode reading...

 

[JdYoda]

Thanks again for helping and explaining.