Macbook Pro 820-02733 PP3v8_AON

[luckydip]

This machine arrived trashed - someone had lifted all the shields and had a go - a mess. I thought it would be a good learning experience as I've never worked on these before. Most of the mess was around the U5700 area, other areas including CD's looked clean.

Initially when conecting charger - 5V drawing 0.4A - U5700 warming up. Removed it but found Q5820 shoted as well. Ordered all the parts and replaced U5700, Q5820 and Q5840 for good measure.

This area had missing components/pads destroyed etc - restored all I could see.

Started measuring around U5700 in diode mode and noticed the PP3v8_AON measuring 40mV and around 90ohms to ground. Couldn't find any measurements for this board to compare with but looked at 820-02020 (seems similar). Openboard data suggests PP3v8_AON should be 351mV (diode).

Removed R5800,R5820, R5840 to try and see which side the lower resistance was. With these removed I get 333mV on L5800, L5820, L5840 - the other side was around 40mV.

Tried to inject 3v C5895 (PP3v8_AON) no short just a small current draw 0.03A.

Am I barking up the wrong tree, is 40mv/90ohms ok for this power rail? Thanks

[MOD EDIT] Link to schematic - https://www.badcaps.net/forum/troubl...matic-brd-help

[mon2]

What is the voltage to ground of PPBUS_AON @ F5200? If it is not in the normal range, remove all power -> meter in resistance mode -> measure the resistance to ground @ F5200. Post each measurement.

[luckydip]

PPBUS_AON - 12.3V (T2 non com?) , resistance to ground 2Mohm both sides, diode 453mV (820-02020 openboard has PPBUS_AON diode 504mV)

[MOD EDIT] Link to schematic - https://www.badcaps.net/forum/troubl...matic-brd-help

[mon2]

This is M2 based so no T2 chip.

PPBUS_AON = Normal voltage should be around 12.60-13.1V.

Review this webpage:

https://repair.wiki/w/MacBook_Air_A2...w_at_5V_repair

[luckydip]

PPBUS_AON - If the voltage is approximately 12.28-12.35V, it may indicate a communication issue between the SOC and PMICs, or corrupt firmware

Not in DFU mode

PP3v8_AON 0v, voltages around U5700 seem ok, P3V8AON_PWR_EN present, PP5V2_P3V8AON_VDRV 0v which comes from PP5V_S2 - will this be needed for the CD's as well?

Looking at the CD's no LDO voltages, PP5V_S2_UPC 0v - generated from UF800. No enable signal from UF840.

Inputs to UF840:

PMU_SYS_ALIVE_1V8 - 100mV
UPC01_5V_EN - 0V

PP1V8_S2 0V. Looks like this comes from U5200. Current sensing resistors ok, is it worth changing the U5200?