820-01700 no power; P5VG3S_EN missing

[randomusername7]

Laptop has experienced some unfortunate liquid damage. It was immediately powered it off, and once I was able, disconnected the battery. There was some corrosion present near the vents, which was cleaned off using 91% isopropyl alcohol and a new soft-bristle tooth brush, but after thorough drying, the laptop wouldn't boot (no fans, no screen, nothing). I managed to get the laptop into DFU state to try and revive it, but experienced an error transitioning from DFU state to DFU state (error code 4042).

5v line (PP5V_G3S) is not coming up. I think I've narrowed it down to the U7800 not creating the P5VG3S_EN signal.

readings from U7800 (sym 1 of 4) are below:

PP3V3_G3H_SOCPMU: 3.4
PP1V1_SLPS2R: cycling between 0 - 1.1
PP3V3_G3H_RTC_X: 3.4
PP1V8_SLPS2R: cycling between 0 - 1.8
PP3V3_G3H_PMU_VINRTC_R: 3.4
PP3V3_S5: 0
PP3V3_AWAKE: cycling between 0 - 3.3
PMU_VPUMP: 5
LDO_RTC: 1.5
PP1V05_S0SW: 0
CPU_C10_GATE_L: 0
PMU_LDO3_OUT_R: 1.8
PP1V2_AWAKE: cycling between 0 - 1.2
PP3V0_G3H_RTC: cycling between 0 - 3.1
PP0V8_SLPS2R: 0.8
LDO_CORE: 1.59

Any pointers?

[RafiManch]

Re: 820-01700 no power; P5VG3S_EN missing

This is the guide what I use:

Differential diagnosis for PP5VG3S_EN missing:

• Device stuck in DFU or Recovery mode.

• Corrupted T2 Firmware or corrupt T2 ROM.

• Failed T2 chip.

• Failed PMU (U7800).


➤Diagnostic Steps:

1. Check if the device is stuck in DFU or Recovery mode.

- Plug the MacBook into another Mac or MacBook via its master port (Left side, bottom port, closest to the trackpad) and open Apple Configurator 2 to verify that it is or isn't in DFU mode. If the device is in DFU mode, Proceed to "Device stuck in DFU mode due to corrupt T2 firmware" in repair steps below.

2. Check voltages that U7800 outputs.

- PP1v8_SLPS2R - Normal voltage ~1.8v "- PP1v1_SLPS2R - Normal voltage ~1.1v "- PP0v9_SLPDDR - Normal voltage ~ 0.9v "- PPVDDCPU_AWAKE ~ Normal voltage ~ 1.06v - PP0v82_SLPDDR ~ Normal voltage ~ 0.82v

If any of the above rails is missing, U7800 may be bad, the rail may be shorted, or the T2 may not be communicating with U7800. Many of these rails have very low resistance to ground as they power the CPU portion of the T2. Do not assume you have a short until you have compared it to a known good board. Many of these rails will read 50-100 Ω to ground. PP1v8_SLPS2R is an exception, with its resistance normally being well within kilo-ohms.

A missing SLP or AWAKE voltage listed above without a short to ground (Less than 10 ohms usually), with P5VG3S_EN missing is suggestive of an issue with U7800.

3. If all SLP and AWAKE voltages are present at their normal voltages, the T2 may not be communicating properly with U7800. Attempt to force the device into DFU mode to reflash the T2's firmware. Proceed to repair steps below for "Forcing device into DFU mode to reflash T2 firmware"


➤Repair Steps

Device stuck in DFU mode due to corrupt T2 firmware:

- Revive T2 firmware via Apple Configurator 2.

NOTE: You must be running the latest version of MacOS for this to work consistently. Check for MacOS updates prior to reviving/restoring T2 firmware.

How to revive T2 firmware: Plug the device you are working on to another Mac or MacBook via its master port. The master port on the A2179 is the bottom left side USB-C port (closest to the trackpad.) If you are confused, please see the diagram listed on Apple's how to page - [6]


Once plugged in, open Apple Configurator 2. You should see a big square icon pop up that says "DFU" or rarely, "RECOVERY". Click the icon, Navigate to the top menu bar click "Actions" then "Advanced". Select Revive device. You will see a progress bar appear. This process can take anywhere from 2 minutes to over 30 minutes in some cases.

SELECTING RESTORE WILL WIPE ALL USER DATA!

Missing SLP or AWAKE voltage without the presence of a short to ground

REMEMBER, Many of the SLP and AWAKE lines will naturally have low resistance to ground !!

- Replace U7800.

Missing SLP or AWAKE voltage with the presence of a short to ground.

Unfortunately, many times when a SLP or AWAKE voltage is shorted to ground, it will be due to a failed T2 chip, which would render the board beyond repair, however in some cases, a capacitor, or U7800 itself will be the cause of the short circuit.

- Use short detection strategies to find the short circuit and replace the shorted component. Do not inject a higher voltage than the line creates. Example: Do not inject higher than 0.82v on PP0v82_SLPDDR

To learn how to use various short detection strategies, see this page - [7]

Forcing the device into DFU mode to reflash T2/BridgeOs firmware

• Attempt to restore BridgeOs firmware via Apple Configurator 2 by placing the device into DFU mode.

- STOP! Before you begin, is your Mac on the LATEST VERSION of MacOs? If not, update your system before proceeding. Forcing a MacBook into DFU mode, and attempting to restore BridgeOs firmware on a old version of MacOs may result in a bricked device.

➣ Follow the instructions on this Apple support article on how to revive or restore T2/BridgeOs firmware, including on how to force a Intel based MacBook into DFU mode by using a key combination. [8]

If the device fails the firmware revive or restore, the T2 chip or U7800 may be the cause of the failure.

If all SLP and AWAKE voltages are present, and a DFU revive fails, replace U7800 empirically. If the problem persists after replacing U7800, the T2 chip is the likely cause of the fault, and a diagnosis of a failed T2 chip can be made.