A2159 2019 13" MacBook Pro

Troubleshooting backlight problems on the 820-01598 is identical in process to all the other USB-C boards from 2016-2020.

Occasionally, with 820-01598 boards with failed U7710/U8110 (GAY/GAV marked ICs) backlight failure will proceed the no power fault. In these cases, U8400 is almost always the cause of the problem.

The backlight circuit is very commonly affected by liquid damage on the 820-01598 board. In these cases, replace all visibly corroded components.

Differential diagnosis for no display backlight on the 820-01598 logic board:

•Failed display TCON board.

•Failed display LED strip.

•Short to ground on backlight output caused by a failed output decoupling capacitor.

•Failed backlight driver (U8400)

•Backlight driver circuit fault (resistors, traces, capacitors, MOSFETs.)

•Low voltage on PP5v_S0SW_LCD

•SMC_LID_LEFT or SMC_LID_RIGHT voltage too low due to a failed hall effect sensor or a issue within the SMC_LID circuit. (Very Rare).

The most common cause for a 820-01598 to have no backlight in the absence of liquid damage, is a short to ground on backlight output due to a failed capacitor.'

➤Diagnostic Steps

1. Check for a short to ground on backlight output (PPVOUT__S0_LCDBKLT_F). C8468 or adjacent capacitors in the series is an appropriate area to measure, since it does not require removal of the system board. If a short to ground is measured, unplug the display connector to rule out a potential short to ground within the TCON board or LED strip of the display. If the short is persistent with the screen unplugged, proceed to the "Backlight output shorted to ground" repair steps below.

2. If no short to ground is measured, and there is no signs or history of infiltrative liquid damage to the system board, test the device with a known working display. If the device has backlight with a known working display, proceed to the repair steps below for "Device has backlight output on a known good display, but not on the originally installed display" below.

3. The following section will focus on determining if U8400 is the cause of the backlight issue.

Failure of U8400 without the presence of liquid damage is uncommon, however if you have no backlight with a known good display, and do not have a short on backlight output, U8400 may be bad or you may have another circuit fault such as a bad resistor or broken trace within the U8400/backlight generation circuit.

If U8400 is corroded, replace it along with any other corroded resistors or capacitors adjacent to it.

It is also common for current sensing pins (pins 9 and 10) of U8400 to be very corroded with corresponding pad/trace damage. If this is the case, run a wire for each pad and connect them to the corresponding probe points adjacent to C8463/61

①. Ensure that the backlight circuit has its input voltage (VIN) by measuring on BOTH SIDES of F8400, which is the backlight fuse. Voltage on both sides of the fuse should be equivalent to PPBUS_G3H. If voltage is normal on both sides of the backlight fuse, proceed to the next step. The backlight fuse can blow in response to a previous short to ground in the backlight circuit, or due to the screen being plugged in without the battery disconnected. Rarely, the backlight fuse can become open (blown) due to development of sulfur deposits on the fuses' filament , or due to micro manufacturing defects on the fuses filament. If the backlight fuse is blown, check for a short on backlight output (PPVOUT_S0_LCDBKLT_F) and on backlight input (PPVIN_S0SW_LCDBKLT_F). If the fuse is blown, proceed to the "Backlight fuse (F8400) blown in the absence of a short to ground" repair steps below.

② Check that the backlight circuit is being enabled. The screen will need to be connected for the enable signal to be sent out. With the board on your bench, with a known good screen connected, measure voltage on pins 1 and 2 of R8442. You should have ~3.3v. Low voltage on pin 2 of R8442 is suggestive of an issue with U8400. If you have 0v on pin 1 of R8442, the backlight circuit is not being told to turn on, which raises the possibility of a CPU issue, or an issue with the display cable/connector.

③ Check the 5v inputs to U8400 (PP5v_S0_BKLT_D and PP5v_S0_BKLT_A).

PP5v_S0_LCDBKLT_D can be measured on R8444 and PP5v_S0_LCDBKLT_A can be measured on R8445. Be sure to check voltage on both sides of the resistor. If voltage is lower on one side of the resistor, R8444 or R8445 is likely blown, probably due to a short within U8400.

If PP5v_S0_LCDBKLT_D or A is low (Substantially lower than 5v), replace U8400 AND R8444/45 as R8444/45 acts as a current limiting resistor to protect PP5v_G3S, and likely blew as a result of an internal short within U8400.

If you have low voltage on pin 2 of R8442 with normal voltage on pin 1 of R8842, replace U8400.

If VIN, EN, and PP5v_S0_LCDBKLT_D are all present at normal levels, and you do not have backlight, replace U8400.

If EDP_BKLT_EN is missing, U8400 is NOT your issue.

➤ Repair Steps

Backlight output shorted to ground:

- Find and replace shorted component.

Ensure the short is not caused by the display. Be sure to measure with and without the display connected.

Most commonly, a short on backlight output is caused by a shorted capacitor. If you have a short on backlight output, solder a wire to a sturdy component that can handle a good amount of current, usually one of the backlight output capacitors (C8468 or C8461 is usually a good spot.) Inject 10v at 5 amps and thermally image the system board or deploy comparable short detection methods. For more information on short circuit detection, please see the following page - [1]

Device has backlight output on a known good display, but not on the originally installed display

- Replace the display assembly.

Backlight fuse (F8400) blown in the absence of a short to ground

- Replace the backlight fuse with a fuse from a donor board or a compatible replacement. (0603 package size, 3 amp, 32v fuse. Brand does not matter.)

Before applying power be sure to double check for a short to ground. Check for a short to ground on backlight output and backlight input.

Try power button reset. Then try SMC reset. If neither has effect, disconnect battery or discharge battery to 0.

The SMC update during a MacOS upgrade may silently fail leaving no power access to the USB ports. This happened to the author after a Catalina 10.5.7 update. Multiple power button resets and SMC resets may not work. Genius bar is baffled. Disconnecting/discharging the battery to 0 allowed the SMC to fully reset.

Differential Diagnosis for this symptom on the 820-01598

• Failed U7710/U8110

• Failed CPU

This is a signature fault on the 820-01598 and 820-01987 logic boards. The VCCIO (U8110) and EDRAM (U7710) buck converter controller ICs fail in unison, resulting in a no POST/boot condition. You will often observe that the fan spins briefly and the amperage (as measured on the USB C amp meter) will settle around 200ma (0.20a).

➤Diagnostic Steps

Measure PP0v95_S0_CPUVCCIO_REG_R on L8102. If voltage is present, this is not your issue. If voltage is missing, proceed.

•You do not need to check EDRAM voltage as this is only requested during high load situations by the CPU via serial communication.

•If PP0v95_S0_CPUVCCIO is measured to be missing:

Check the PVCCIO_EN signal at R8165 - It should be present at 3.3v.

Check the PPVCCEDRAMS0_EN_FILT_BUF signal at pin 1 of R7766 - It should be present at 3.3v

➤Repair Steps

• If both enable signals are present, and PP0v95_S0_CPUVCCIO_REG_R is missing, replace BOTH U7710 and U8110.

Typically, when this fault occurs, you will have either no backlight or no camera function after the repair. It is unknown why this happens, however it probably is related to either the backlight driver serial communication or camera serial communication somehow overloading parts of the CPU, causing it to draw more power than the chips are rated for causing this issue.

If the device has no backlight after the repair: -Replace U8400

If the device has no camera function after the repair: -Replace the display assembly

The most likely cause for a 820-01598 to be stuck on 5 V and low current draw (~0.00–0.02 A) on the USB-C current meter is a short to ground on PPBUS_G3H. However, if all ports are not reading the same, then it may be indicative of a CD3217 issue. In order to identify the root cause, a differential diagnosis must be conducted including looking for absent PPBUS_G3H voltage due to a short or creation problem, a device stuck in DFU mode due to corrupt T2/BridgeOs firmware, an absent or shorted PP3v3_G3H_RTC voltage, a failed CD3217 USB C controller, a short to ground on any of the power rails generated by U7800 that power the T2 chip, a missing U7800 input power, a missing or shorted SLPS2R line, and any non-specific areas of corrosion causing T2 or CD3217 communication issues.

Occasionally, after liquid damage, this series of board may develop an internal PCB substrate short in the area of C6905/C6900. This is usually not repairable as the area has many small traces within the area of the board that is typically effected. This fault will typically be visible as PCB damage around U6900/U6905 which may include melted copper, solder balls or a visibly burned area. You can try and resect the short using a blade, however the short will typically extend through all layers of the board, and typically will not be repairable.

Possible diagnoses for 5 V and low current draw as indicated on the USB-C current meter

•Absent PPBUS_G3H voltage due to a short or creation problem.

•Device stuck in DFU mode due to corrupt T2/BridgeOs firmware.

•Absent or shorted PP3v3_G3H_RTC voltage.

• Failed CD3217 USB C controller (U3100 or U3200

•Short to ground on any of the power rails generated by U7800 that power the T2 chip, such as PP1v8_SLPS2R or PP1v1_SLPS2R. (Rare on this board.)

• Missing U7800 input power.

• Missing or shorted SLPS2R line. (Most commonly PP1v8_SLPS2R due to a short to ground.) (Rare on this board.)

• Non-specific areas of corrosion causing T2 or CD3217 communication issues.

➤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 voltage on PPBUS_G3H.

To accurately measure voltage on PPBUS_G3H, set your multimeter to DC voltage mode and place the black probe to ground and the red probe on PPBUS_G3H. For the 820-01598, the ideal measurement point is F7000.

~12.60–12.65 V = Normal

~12.28–12.35 V = T2 communication issue with the ISL9240. The likely cause for this is the device is stuck in DFU mode due to corrupt T2 firmware or a failed CD3217. Proceed to repair steps below for corrupt T2 firmware.

~0 V = Short to ground or absent voltage due to a creation problem. Proceed to repair steps below for shorted or absent PPBUS_G3H voltage.

3. Check PP3v3_G3H_RTC voltage.

- Ensure your multimeter is in DC voltage mode. ( Straight line with 3 - - - under the line. ) Place the black probe on ground and the red probe on PP3v3_G3H_RTC. It is recommended to measure PP3v3_G3H_RTC on a capacitor or resistor near one of the CD3217s to rule out a trace/via issue. C3200 is a good place to measure this line on the 820-01598 logic board.

~3.3 V (3.290–3.425 V) = Normal.

4. Check PP3v3_G3H_PMU_VDDMAIN voltage.

- Ensure your multimeter is in DC voltage mode. ( Straight line with 3 - - - under the line. ) Place the black probe on ground and the red probe on PP3v3_G3H_PMU_VDDMAIN. It is recommended to measure PP3v3_G3H__PMU_VDDMAIN on a capacitor near U7800 to rule out a trace/via issue. C7891/C7807 is a good place to measure this line on the 820-01598 logic board.

~3.3 V (3.290–3.425 V) = Normal.

Values below the above spec should be considered abnormal. Proceed "PP3v3_G3H_PMU_VDDMAIN low or absent" in the repair steps below.

➤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 A2159 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 - [2]

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!

PPBUS_G3H Short to ground:

Inject around 1 V with a 5 amp limit into PPBUS_G3H with a DC power supply. A larger tantalum capacitor or the main PPBUS fuse (F7000) is preferred to inject voltage to, as you will often need a lot of current to be pushed into the line to cause the shorted component to heat up. 1 V is usually sufficient. It is not recommended to inject over 1 V as if one of the CPU VRMs is shorted, you will end up killing the CPU. A good place to inject voltage to on the 820-01987 is F7000.

With voltage being injected, perform thermal imaging of the board. If thermal imaging is not available, feel around the board to see where it is getting warm. Once the area is localized, add a small amount of isopropyl alcohol to the area to localize the shorted component.

Once the shorted component is localized, replace the shorted component.

Most commonly, you will find one of the capacitors near the speaker connectors to be shorted to ground. (Typically C6405, C6456 , C6555 or C6556.) If this is the case, remove the capacitor. It does not have to be replaced.

For more info on finding short circuits, please see - [3]

PPBUS_G3H Absent or low with no short:

If PPBUS_G3H is absent, first check that PPDCIN_G3H is making it to the Intersil/Renesas ISL9240 (U7000). Measure PPDCIN_G3H with a multimeter in voltage mode at C7024, C7029, C7028, or C7026 on 820-01598. The voltage should match that of the USB-C amp meter (5 V). If 0V is read, check for a short, and if none is found, move to "CD3217 troubleshooting" in the repair steps. If 5 V is read, check the current sensing resistors (listed below) as the ISL9240 may have shorted internally causing the current sensing resistors to blow. Place the multimeter probes on each side of the resistors to measure the resistance, which should be within 5–10% of the reference. If a resistor is found out of spec, replace it and the ISL9240, as the resistor likely blew due to an internal short. Depending on the input voltage, the ISL9240 either buck or boosts the voltage to ~12 V; if USB-C voltage is 5 V, it boosts it

R7021 — 1.00 Ω

R7022 — 1.00 Ω

R7061 — 1.00 Ω

R7062 — 1.00 Ω

If the current sensing values are normal, replace the ISL9240 (U7000)

PP3v3_G3H_RTC low or absent:

The PP3v3_G3H_RTC voltage powers the "brain" of the CD3217 USB-C controllers, enabling communication with the USB-C charger to allow for 20 V. If PP3v3_G3H_RTC is shorted, low, or absent, the communication between the charger and the device cannot take place, resulting in the device being stuck at 5 V. On the 820-01598, the buck converter U6903 is responsible for lowering the voltage from PPBUS_G3H (approximately 12 V) to 3.3 V to generate PP3v3_G3H_RTC. Therefore, in order to get PP3v3_G3H_RTC, PPBUS_G3H must be obtained first.

•The most common reason for PP3v3_G3H_RTC to be missing or low, is a short to ground, usually on a capacitor around one of the CD3217s, or from a CD3217 itself.

•If PP3v3_G3H_RTC is not shorted, confirm that the enable signal GHGR_EN_MVR is present, which is generated by the ISL9240 (U7000). The ISL9240 often fails in such a way that prevents GHGR_EN_MVR from being produced. If the enable signal is missing, replacing the ISL9240 (U7000) is recommended. Additionally, due to the capacitance of the circuit, PP3v3_G3H_RTC may falsely read as short, measuring around 100 ohms. This should be considered a false positive. To confirm, remeasure the PP3v3_G3H_RTC after the board has been removed from power for a few minutes.

•PP3v3_G3H_RTC can also be pulled low by PP3v3_UPC_XB_LDO or PP3v3_UPC_XA_LDO, so if you have no measurable short to ground, and your enable/VIN is present, check both the above rails for a short or low resistance to ground. Low resistance to ground/short on the above LDO lines will usually be caused by a bad CD3217.

• Occasionally, U6903 may PPBUS_G3H to ground and may blow it's VIN current limiting resistor U6900. Be sure to check voltage on both sides of U6900 if you suspect your VIN may be missing to U6903.

If you found and resolved a short circuit, and still have low voltage on PP3v3_G3H_RTC, check voltage on both sides of R6934/35. These resistors can blow in response to a short circuit.

Possible diagnoses for this symptom can include corrupted BridgeOS firmware (Most common), a bad touchbar, or bad T2 chip.

Most cases of this symptom will be related to corrupted BridgeOS firmware and will be resolved via a DFU revive or restore. If a device displays this symptom: Attempt to restore BridgeOs firmware via Apple Configurator 2 by placing the device into DFU mode. Solder a wire across SE032 (Omitted/No Stuff) to pull SOC_FORCE_DFU high. Wire should be across pins 3 and 4 or 1 and 2. - 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.

NOTE: Selecting restore will wipe all user data.

➣ 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. [4]

If a DFU Revive or Restore does not resolve the issue, try placing the board in a known good top case or replace the touchbar/top case.

If the issue still is not resolved after touchbar replacement, the issue is likely related to the T2 chip's internal GPU and cannot be repaired without replacing the system board, or replacing the T2 chip. (Not recommended.)

Differential diagnosis for camera detection issues on the 820-01598 logic board:

Failed webcam on display assembly. Most common especially after U7710/U8110 failure.

•Failed TCON board, resulting in PP5v_MAIN_ALSCAM being shorted to ground, which usually presents as a catastrophic failure of L8504. Usually, when this fault occurs, the TCON board is seen with a burned camera connector with occasional PCB layer damage.

•Corrupt T2/BridgeOs firmware. This is rare.

Failed camera secure disable chip (U8502). This is very rare.

Corroded display connector/cable.

➤ Diagnostic Steps:

1. Check continuity on L8504.

- Place your multimeter in continuity mode and measure across the component. L8504 is a filter, so it is essentially a wire. Your reading should be close to 0.01. You will often find this component visually exploded/burned with adjacent trace damage. If L8504 measures normally, proceed to the next steps. If L8504 is blown or burned, proceed to the "L8504 blown or visibly burned repair steps below."

2. Check camera function with a KNOWN GOOD display.

- You don't have a board issue until you know you don't have a parts issue. If L8504 measures normally, test with a known good display, or place the board in a known good housing. If the camera works normally with a different screen/enclosure, the display is the issue and will need to be replaced. BE SURE TO CHECK L8504 FIRST!

➤Repair Steps

Camera works with a known good test display

• Replace the display assembly.

L8504 blown or visibly burned

Understand that this fault occurred because of a catastrophic short within the TCON board of the display. or from a corroded display cable/connector which melted and shorted the 5v camera line to ground. If you repair L8504 without addressing the display issue, L8504 will fail again.

• Generally, when L8504 blows, there will be corresponding pad and trace damage and jumper wires will usually be required.

- 36 or 37 AWG enamel coated copper wire is recommended for jumper wires in this application due to the power requirements of the webcam and ambient light sensor, which are both powered off this filter.

- The closest recommended jumper point for the input side of the filter (PP5v_G3S) is C5250, which the input side of the filter can be directly connected to.

- Using a conformal coating on the jumper wire is strongly recommended.

- Use a 120 Ohm ferrite filter rated for 1.5 amps in a 402 package size only, preferably from a donor board. Do not substitute a resistor, wire or fuse.

- After L8504 is replaced, and jumper wires are run as needed, replace the display assembly, or repair the display assembly by replacing corroded/burned cables and connectors as necessary.

No camera function, L8504 measures normally, and the camera still does not work when tested with another display.

• 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. - [5]

• If you still have no camera function after a T2/BridgeOs firmware revive/restore, and you have ruled out other causes listed above, the camera secure element (U8504) may be bad, or you may have a non-specific trace/resistor issue between the camera connector/U8504 or between U8504 and the T2 chip. A hardware issue with the T2 chip can also cause no camera detection issues.

This issue is often caused by a short to ground on a subrail, which can be accurately detected with a high resolution thermal imaging scan. Low resolution thermal imaging may not reveal the subtle signs of a small shorted component, making it a less reliable diagnostic method.

➤Diagnostic Steps

Perform High Resolution, High Sensitivity thermal imaging of the entire system board. Low resolution thermal imagers will likely not pick up the subtle temperature changes failures like this often present with. The failure will often present as a component quickly heating up and cooling down in sync with the amperage changes; Occasionally, you will find a resistor heating up/cooling down in sync with the amperage changes. The short is likely caused by something on the output side of the resistor.

➤Repair Steps

Remove and Replace the shorted component based on thermal imaging findings.

Differential diagnosis for no power, with 20v and ~0.03-0.06 as measured on a USB-C amp meter.

• Failed T2 or NAND (Most likely diagnosis for most cases in the absence of the below causes.)

• Device stuck in Recovery mode due to prior failed DFU revive. (Most common.)

• Short to ground on PP3v3_S5.

• Corrupt T2/BridgeOs firmware.

• Failed PMIC (Rare.)

• Shorted or Absent SSD voltages.

• Corroded Ocarina PMIC. (U9000)

➤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 or recovery mode due to corrupt T2 firmware" in repair steps below.

2. Check for a short to ground on PP3v3_S5.

- If a short to ground is found, proceed to the "PP3v3_S5 short to ground" repair steps below.

3. Check resistance to ground on PP2v5_NAND_SSD_0. (Normal values can be as high as >1MΩ or as low as 60Ω. In the case of SSD/NAND failure, resistance will usually be between 1-3Ω.)

4. Inspect U9000 for corrosion. The location of the chip on this board makes it prone to corrosion, either from liquid ingress or from condensation from dust collection. U9000 can be reballed if corroded which will likely resolve the issue if it is corroded.

➤Repair Steps

Device stuck in DFU mode due to corrupt T2 firmware:

- Revive or restore 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 A2159 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.

It is important to note, if the device is in Recovery mode, the end user may have brought the device to another repair shop or Apple first, who attempted a DFU revive which failed. You may have a secondary issue if the revive fails again.

Possible causes for a device to fail a DFU revive:

- Short to ground on PP2v5_NAND_SSD_0)

- Absent U9000 voltages. (PP0v9_SSD_0, PPVCCQ_ANI_SSD0 (1.8v)

- Failed Trackpad (Will almost always show the Apple logo before failing the process.)

- Failed NAND

- Failed T2 or T2 RAM.

If no secondary causes are found, a DFU Restore may resolve the issue.

SELECTING RESTORE WILL WIPE ALL USER DATA!

PP3v3_S5 shorted to ground.

- Locate and replace the shorted component.

PP3v3_S5 is a tricky line to inject voltage to on this board, as most components are small 0201 parts. Be sure to use a small gauge wire to inject voltage if you choose to inject voltage to a 0201 part. The best place to inject voltage to on this board is pin 5 of U4801.

1v at 5 amps is an appropriate voltage to inject into the line. Remove the heatsink prior to injecting voltage as occasionally, the CPU will be the cause of the short to ground.

With voltage being injected, perform thermal imaging of the board. If thermal imaging is not available, feel around the board to see where it is getting warm. Once the area is localized, add a small amount of isopropyl alcohol to the area to localize the shorted component.

Once the shorted component is localized, replace the shorted component.

For more info on finding short circuits, please see - [7]

U9000 visibly corroded or damaged.

- If corroded, reball the IC. Replacement is usually not necessary.

- If physically damaged or burned, replace the IC. The IC is not programmed and can be taken from any board which utilizes the same part. (338S00410)

If no short is found on PP3v3_S5, and the device is not in DFU or recovery mode, and all other findings are negative, you can try forcing a firmware revive.

• Attempt to restore BridgeOs firmware via Apple Configurator 2 by placing the device into DFU mode. Solder a wire across SE032 (Omitted/No Stuff) to pull SOC_FORCE_DFU high. Wire should be across pins 3 and 4 or 1 and 2.

- 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.

NOTE: Selecting restore will wipe all user data.

➣ 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 one of the NANDs is likely dead or is receiving unstable power from the PMIC (U7800) causing it to crash. If the device fails the firmware revive, you can try empirically replacing U7800. You must removal the large shield covering U7800 and the T2 chip prior, which is not easy. You must use low melt alloy to remove the shield. Be careful not to bridge surrounding components. Go slow and be patient.

Replacing U7800 should be seen as a last ditch effort, as it only works in a small amount of cases, and does not have a definitive diagnostic test to determine if it is bad.