820-02098 5V

[No-Clean]

This Machine seems to have been dropped more than a few times, came in powering on but with no image on internal display, we did have image on external display, it did have backlight but no image on internal display. After doing some testing we found out that the display connected to a working Mac also has the same issue, BUT when the screen was re-installed back on the dropped Mac that Mac now is stuck at 5V.

Clean board
Does not enter DFU
No light on charger
PPBUS not shorted and 12.3V

I don't know where to take it from here, please be patient.

 

[2informaticos]

If machine was droped, probably broken traces, or solders under BGAs.
First check for knocked off components.

Do you get voltages around U7700/8100 PMUs?
3V8_AON is present?

 

[No-Clean]

Looked all over, no knocked components.
3V8_AON 3.7V
No voltages around U7700/8100, some fluctuate a little, but none are stable or higher than 1V
Already gave both PMUs a reflow with good flux but no luck.

 

[2informaticos]

Check U8100 LDOs (page 41).
If any missing, check diode mode to ground.

 

[No-Clean]

The ones that are different from a working board are:

PP3V8_AON_MPMU_ISNS measures 0.350 vs 0.190 last one is good board but It does have its 3.8V
PP1V2_S2 fluctuates fast under 1V, diode read ok
PP3V3_S2 fluctuates fast under 3V, diode read ok
PP1V8_S2SW_CLVR_VDDC1_LDO fluctuates fast under 1V, diode read ok
PP3V3_AON fluctuates fast under 3V, diode read ok
PP0V8_S2_CLVR_VDDDIG fluctuates fast under 1V, diode read ok
PP1V8_AON 1.8V
PP1V2_AON 1.2V
PP1V5_AON_VCORE_MPMU 1.5V

NC_PPVOUT_LDO0_MPMU and NC_PPVOUT_LDO3_MPMU and NC_PPVOUT_LDO6_MPMU not on boardview I assume this are NC No connect.

I also took the time to add and submit the measurements for the community via PDaniels software.

 

[2informaticos]

PP3V8_AON_MPMU_ISNS is stable?
If yes, then U8100 is suspect.

 

[No-Clean]

Yes PP3V8_AON_MPMU_ISNS stable at 3.7V
I will check to see if I can get this IC somewhere

 

[No-Clean]

Ok I got the new chips and have already installed them both U8100 and U7700 but the behavior is the same.

Now I have also noticed that PPVDD_DISP_AWAKESW is 0.070 and PPVDD_SOC_S1 is 0.040 in diode reading and if I am not mistaking this should be 0.199 and 0.130

For now this has turned into a learning project so lets see if we can get to it.

 

[2informaticos]

Did you check these values before replacing the chips?

Both voltages come out from U7700.
You can lift corresponding coils and check where the low values remain.
I bet for U7700...