A2179 820-01958 power up sequence: PMU_PVDDMAIN_EN always 0

[Unkraut]

Dear all,

I'm trying to fix an Apple A2179 (820-01958).

The laptop had water poured over it while it was on. The audio board was corroded. The VBUS pins on the connector were completely eaten away. The main board shows no signs of corrosion, but most likely was also exposed to water. Also the water corrosion on the audio board might have led to damage on the main board.

I tried first to check all pins coming from the audio board to the main board using the component tester of a Hameg HM303-6 to see if there is any damage. All looks fine. I see protection diodes.

I disconnected the main board from everything except the battery. I plugged in a USB-C charger which activates the main boards power sequence.

In the power up sequence I see that form PP1V8_SLPS2R on, the voltages pulse. PP1V8_SLPS2R is on for approx. 4s off for ~1s.
PMU_PVDDMAIN_EN always stays below 0.001V. The component tester shows that PMU_PVDDMAIN_EN is partly actively driven to 0 by an output, partly driven by a pull-down. Triggering the HM303-6 on the PMU_PVDDMAIN_EN never shows any trigger.

When voltages I see when supplies are on are the following:

• PBUS (PPBUS_G3H) => ~ 11.3V
• PP3V3_G3H_RTC 3.28V
• PP3V3_G3H Varying, 3.22 to 2.29V depending on how much current is drawn.

• PP1V8_SLPS2R 1.80V
• PMU_CLK32K_SOC ⇒ Oscillating, freqeuncy matches approxiamtely
• PP1V8_AWAKE 1.80V
• PP1V8_SLPS2R_PMUGPIO 1.8029
• PP1V1_SLPS2R 1.1026
• PP0V8_SLPS2R 0.8012
• PP0V82_SLPDDR 0.8227
• PP3V3_AWAKE Varrying 3.22 to 3.26V
• PPVDDCPUSRAM_AWAKE 0.8005
• PP0V9_SLPDDR 0.8984
• P1V1_SLPDDR_SOCFET_EN 1.8027
• PP1V1_SLPDDR 1.1026
• H9M 24MHz CLK ⇒ Oscillating, freqeuncy matches approxiamtely
• PP1V2_AWAKE 1.211
• PPVDDCPU_AWAKE 0.7555
• PMU_SYS_ALIVE 1.7836
• PMU_ACTIVE_READY 1.7977
• PMU_COLD_RESET_L 1.79

The power sequence diagram says as next: "H9M LOAD SECURE ROM, SMC BATTERY TRAP"

I've checked the SoC ROM U4770. Data is being transferred on the MISO line. The transfer is complete seconds before all voltages break down and the power cycle restarts.

I don't see any activity on the I2C bus to the battery. However, voltages seem fine.

Checking the voltage drops along the GND I see the main consumer is the T2. The maximum voltage drop is ~50µV.

This is where I'm stuck and don't know how to move further .

I think the T2 is booting fine. I'm asking myself is what the battery trap should be and how to check that.

Please help!

[macabook]

Hi, did you manage to solve the issue, I have exactly the same readings not able to get into DFU

[mon2]

PP3V3_G3H should be stable. Remove all power. Meter in resistance mode. Measure the voltage to ground of PP3V3_G3H.

[mon2]

Sorry..Measure the resistance to ground of PP3V3_G3H.

[macabook]

Thank you, let tell some details about my issue, it's a MacBook pro A2141 EMC 3347. not powering on, the USB C meter shows 5.162 V on all 4 ports and starts consuming around 70 mA than stable at around 60 mA after 30 second. All ports behave the same. No sign off liquide damage the board is looking very clean. The mac is not in DFU mode, I tried key combination and by forcing it on the board SWK003 no DFU mode showing either by charger or only from host (actually the batterie is flat)
My readings and symptoms are not exactly the same as the original post the power sequence stop at PMU_PVDDMAIN_EN, I dont have oscillation on PP3V3_G3H_T. Here are the details according to openboardview sequence:

[n:PBUS] PPBUS_G3H 12.28 V
[n:PP3V3_G3H_RTC] PP3V3_G3H_RTC_X 3.38 V
[n:PP3V3_G3H] PP3V3_G3H_T 3.37 V

VIN_RTC > VIN_RTC_UPPER_THRESHOLD
[n:PP1V8_SLPS2R] 1.8 V

[n:PMU_CLK32K_SOC] 0.87 V
[n:PP1V8_AWAKE] 1.80 V
[n:PP1V8_SLPS2R_PMUGPIO] PP1V8_SLPS2R_PMUVDDGPIO 1.80 V
[n:PP1V1_SLPS2R] 1.10 V
[n:PP0V8_SLPS2R] 0.79 V
[n:PP0V82_SLPDDR] 0.82 V
[n:PP3V3_AWAKE] 3.37 V
[n:PPVDDCPUSRAM_AWAKE] 0.80 V
[n:PP0V9_SLPDDR] 0.90 V
[n:PP1V1_SLPDDR_SOCFET_EN] P1V1_SLPDDR_SOCFET_EN 1.80V should it be 1.1 ?
[n:PP1V1_SLPDDR] 1.10 V
[n:H9M_24MHz_CLK] DONT KNOW WHAT TO CHECK
[n:PP1V2_AWAKE] 1.19 V
[n:PPVDDCPU_AWAKE] 0.75 V
[n:PMU_SYS_ALIVE] 1.78 V
[n:PMU_ACTIVE_READY] 1.79 V
[n:PMU_COLD_RESET_L] 1.79 V

H9M LOAD SECURE ROM, SMC BATTERY TRAP
[n:PMU_PVDDMAIN_EN] 0V / 19.47 kOHM/ Diode mode 0.676V just after unplugging the charger then after 30 sec it drop OSCILLTING BETWEEN 0.59 and 0.69 then go stable at 0.749V maybe it normal behavior I dont know ?
[n:P3V3MAIN_PGOOD] 2.8 mV /resistance to ground just after unplug charger is 77 ohm that increase slowly until 16.55 KOhm stable (pin 2 R7690). But if I measure resistance on pin1 R7690 I get increasing from 0.5Kohm until 2.8 Kohm then on pin 2 it goes from 0.6 Mohm to 93 Kohm droping very slowly same behaviour every time I jump from pin1 to pin2. R7690 is measured 97Kohm. Diode mode pin1 of R7690 (PP3V3_G3H_T) is 0.362V and pin2 0.542 V. I DON't understand why i don't get P3V3MAIN_PGOOD on pin 2 since I have the PP3V3_G3H_T on pin1 ?
[n:PP3V_G3H_RTC] PP3V0_G3H_RTC 3.00 V
[n:PMU_CLK32K_PCH] 0.866 V
[n:PCH_RTC_RESET_L] 3.00 V
[n:P5VG3S_EN] 0V
[n:PP5V_G3S] 0.8 mV
[n:P3V3G3S_EN] 0 mV
[n:PP3V3_G3S] PP3V3_G3S_T 0 mV
[n:P1V8G3S_EN] 1.1 mV
[n:PP1V8_G3S] 0mV
[n:P5VG3S_PGOOD] 0 mV

Thank you in advance for your help

[mon2]

P1V1_SLPDDR_SOCFET_EN 1.80V should it be 1.1 ?

No. The logic level for the enable is at 1v8 but output of this power rail is 1v1. No issue here.

Is the battery connected or disconnected? This model may need a good battery to boot. Measure the voltage to ground of each pin on the battery connector. Mostly wish to confirm the smbus lines of scl and sda pins.

[macabook]

You mean while I tried entering DFU mode? I tried with and without battery it doesn't help, the battery is completely dead 0V in both pins. I have followed the video on logiwiki same board with disconnected battery and he successfully entered DFU, but he say that he use external power supplly. Did it mean that the charger is not enough and need external power supply on 20v? https://youtu.be/e0jevSCQxGE

what about the question « I DON't understand why i don't get P3V3MAIN_PGOOD on pin 2 since I have the PP3V3_G3H_T on pin1 ? » is it due to a bad chip ?

[mon2]

what about the question « I DON't understand why i don't get P3V3MAIN_PGOOD on pin 2 since I have the PP3V3_G3H_T on pin1 ?

This signal is the power good signal and is common to such regulators. This output is an open-drain type. This means that ONLY if the voltage being monitored is with specifications then this output signal will be left floating. For this reason, there must be an external resistor that is the pull-up resistor that is required to park this floating line to a logic '1' state to denote to the external logic, the voltage is stable and within proper range.

See attached for the local pull-up resistor for this line. Measure the voltage to ground of the pull-up voltage. Same note as post # 3 / # 4. This voltage must be stable - not fluctuating. If this pull-up voltage is fluctuating then there is too much current being drawn on this rail.

After the above check, remove all power -> meter in resistance mode -> measure the resistance to ground of PP3V3_G3H. If the resistance is too low, then there is a shorted part on this rail that needs to be located and removed. Perhaps a bad capacitor.

Confirm that R7601 is not defective and is ~100k ohms across the pads of this part. No power during resistance checks.

[macabook]

Thanks for your explanation.

I have 3.3V in pin 1 of the resistor and 3mV in pin 2.

When I check for short on PP3V3_G3H in pin 1 it start 28 ohm then increasing until 16kohm but sometimes it's in Mohm. In other area it always high resistance

I decided to replace the U7650 and the resistance R7690 (in my case) now I have 5.146V and around 160mA in all USB-C. Then I checked the resistance to ground in PP3v3_G3H is 32 Ohm, everywhere I measure is the same 32ohm, which is a clear short that I have to find now.

[mon2]

Suggest to review the areas linked to removable devices like the LCD. Locate -> flux and remove U8501 which is the power load switch for the LCD display assembly. Perhaps too much current went through this load switch and is now shorted. Keep track of the pin # 1 orientation of this component which is polarized. After the part is removed off the board, test if the resistance to ground of this rail returns to normal or not. Ideally a thermal camera will help here but IPA (alcohol) can also be used to locate the shorted component(s).