820-02020 a2338 5.18v 1.38a no power

[Jeffotskie26]

no sign of corrosion
unable to boot even dfu mode
PPBUS_AON 12.31v stable
sometimes it ables to turn 20v with 1.37amp freeze (very rare)
PPBUS_AON 12.02V
replaced 2 cd3217 chips and u5200 nothing changes.
can you help me what to do next?

 

[2informaticos]

Do you get 3V8_AON?
Check MASTER PMU LDO and BUCKS.

 

[Jeffotskie26]

found shorted on PPVDD_ECPU_AWAKE 0.020 ohms
removed L82B1/B0 still shorted.
i think cpu is fried.

 

[2informaticos]

Any chance to compare the reading with working board?

 

[Jeffotskie26]

yes i have working board to compare i believed the short circuit is coming from cpu.

 

[2informaticos]

If possible (and you have time), please upload a list with diode mode readings on all coils from the working board.
This can help other members in the future.
We have lack of information about these new M1 boards...

 

[Jeffotskie26]

okay will posted it soon. thanks.

 

[TCRScircuit]

found shorted on PPVDD_ECPU_AWAKE 0.020 ohms
removed L82B1/B0 still shorted.
i think cpu is fried.

Not a short. What is resistance to ground on this line?

_________________________________

1.38 amps is too high. Is the battery connected? If so disconnect it. Does the amperage remain high?

 

[2informaticos]

Not really short, but very low resistance comparing with good board; "L82B0/B1 168 PPVDD_ECPU_AWAKE"
So there is a problem with that power line for sure.

 

[TCRScircuit]

Here is normal diode and resistance measurements from a known good board I recorded and posted on repair.wiki. Keep in mind silicon resistance changes with heat. The board must be cold at room temp to get accurate readings. Was the board hot by chance when you measured this? Anything above 100*C will result in vastly different readings compared to room temp.



L8100 / L8101 / L8102 (PPVDD_PCPU_AWAKE) - Normal diode mode to ground reading ~0.007 / ~45Ω

L82B0 / L82B1 (PPVDD_ECPU_AWAKE) - Normal diode mode to ground reading ~0.114 / 140Ω

L8270 / L8271 (PPVDD_CPU_SRAM_AWAKE) - Normal diode mode to ground reading ~ 0.116 / 450Ω

L8120 / L8121 (PPVDD_SOC_S1) - Normal diode mode to ground reading ~ 0.012 / 110Ω

L8110 / L8111 / L8112 (PPVDD_GPU_AWAKE) - Normal diode mode to ground reading ~ 0.010 / 35Ω

L8280 / L8281 (PPVDD_DISP_S1) - Normal diode mode to ground reading ~ 0.055 / 233Ω

L8290 (PPVDD_DCS_S1) - Normal diode mode to ground reading ~ 0.176 / 310Ω

L84E0 - (PP1v4_LDO_PREREG) - Normal diode mode to ground reading ~ 0.285 / >30kΩ