820-03637 A3434 No Power Repair – Severe Water Damage and UF400 Reball

Fault Description

This 14-inch MacBook Pro M5 2025, model A3434, logic board 820-03637, came in from the Clayton VIC 3168 area with severe water damage and no power.

The customer explained that a water bottle opened inside a school bag and liquid ran through the MacBook. The MacBook was turned upside down and left off, then taken to a local repairer. The previous repairer tried what they could, but advised that the MacBook likely needed a new or repaired main board.

Because of the level of liquid exposure, we did not power the board on immediately. The USB-C meter test was skipped at the beginning because applying power to a badly corroded board can turn a repairable board into a non-repairable one.

Case Summary

Item	Details
Device	14-inch MacBook Pro M5 2025
Model	A3434
Logic board	820-03637
Customer area	Clayton VIC 3168
Customer fault	Water bottle leaked in school bag, no power
Initial USB-C test	Not powered on — too risky
Board condition	Top side looked clean; severe corrosion found on bottom side
Reference used	Similar 820-02757 board view / schematic
Initial diagnosis method	Ultrasonic clean, diode-mode checks, voltage injection
Shorted rails	PPBUS_AON and PP5V_S2_UPC
Hot components found	CR604, CR634, CF406, CF506
Corroded parts replaced	25 capacitors, 5 resistors, 2 small IC chips
Post-rebuild USB-C behaviour	Two ports 5V / 0.23A rebooting; one UF400-related port 5V / 0A
Main boot fault	Corrosion under UF400 / SN2012024 balls
Repair	UF400 removed, reballed and reinstalled
Secondary fault	No left-side sound
Audio repair	UR600, UR630 and UR660 replaced
Final fault	Lid angle sensor not working
Final repair	Lid angle sensor replaced
Final result	MacBook fully functional

Initial Inspection

The top side of the logic board looked relatively clean, but after removing the board from the case, severe corrosion was found on the underside.

This is an important lesson. On liquid-damaged MacBooks, the visible side of the board does not always show the true damage. Liquid can travel under the board, under shields, under ICs, around connectors and into hidden low-clearance areas.

The previous repairer had not removed the board for a full underside inspection and cleaning. That is common with general repair shops, even trusted ones, because severe board-level water damage requires specific equipment, experience, schematics/board views and component-level repair skills.

Why We Did Not Power It On First

With severe corrosion, powering the board before cleaning is risky because liquid residue and corrosion can create leakage paths or direct shorts between rails.

Applying USB-C power too early can cause:

a shorted main rail to burn pads or traces;
PMIC or charging-circuit damage;
NAND / CPU-related rail damage;
corrosion to heat up and carbonise;
small repairable faults to become board-killing faults.

For this reason, the first step was ultrasonic cleaning, followed by diode-mode checks on major power rails before any normal power-on attempt.

No 2025 Schematic Available

For this 2025 board, there was no exact schematic available. That made the job harder because there was more comparison work and more careful reasoning required.

The board layout was compared against the older 820-02757 design, which has similar areas for USB-C, power, audio and lid/sensor circuits. It is not the same board, but it gave enough reference direction to make diagnosis possible. The 820-02757 reference includes USB-C controller sections, 5V power regulation, audio sections and lid angle sensor support, which matched the fault areas we later worked through.

In this type of repair, an older similar schematic is not perfect, but it is still much better than working completely blind.

Measurements and Short-Finding Table

Stage	Measurement / Action	Result
Initial USB-C power test	Not performed	Too risky to power on
Major rail check	PPBUS_AON	Shorted
Voltage injection	PPBUS_AON, started at 1V and slowly increased	CR604 and CR634 hot
Action	Removed CR604 and CR634	PPBUS_AON short cleared
Second rail check	PP5V_S2_UPC	Shorted
Voltage injection	PP5V_S2_UPC, started at 1V and slowly increased to 3V	CF406 and CF506 hot
Action	Removed CF406 and CF506	PP5V_S2_UPC short cleared
Rebuild	25 capacitors, 5 resistors, 2 small ICs replaced	No major rail short remaining
First power-on after rebuild	Two ports 5V / 0.23A rebooting	Partial startup attempt
UF400-related port	5V / 0A	Suspicious local USB-C controller fault
Microscope inspection	Corrosion under UF400 / SN2012024 balls	UF400 removed and reballed
After UF400 reball	Mac powered on	Boot restored
Audio test	No sound on left side	Secondary fault found
Audio IC repair	UR600, UR630, UR660 replaced	Sound restored
Lid close test	Mac did not sleep when lid closed	Angle sensor fault
Final repair	Angle sensor replaced and board ultrasonically cleaned again	Fully functional

Why Voltage Injection Was Done Carefully

For the PPBUS_AON short, voltage injection started at 1V and was slowly increased, but not beyond the safe range for that rail.

Because PPBUS_AON is normally a high-voltage main rail, it can tolerate higher voltage than a 1.8V or 3.3V rail, but it is still dangerous to inject too much current or too much voltage into a shorted board. The purpose of injection is not to “power the MacBook”. The purpose is only to locate the shorted part by heat.

On PPBUS_AON, we slowly increased voltage and used the thermal camera. CR604 and CR634 heated up, so they were removed.

For PP5V_S2_UPC, the injection limit was lower. This is a 5V-related rail, so we started at 1V and slowly increased to around 3V. The thermal camera showed CF406 and CF506 heating, so they were removed.

This staged approach reduced the risk of causing extra damage while still allowing the shorted components to be located.

Circuit Logic

This repair had several separate fault stages.

Stage 1: Severe water damage and hidden underside corrosion

The top of the board looked clean, but the underside had severe corrosion. Because of the corrosion level, powering the board was too risky.

Correct first step:

Remove board
Inspect both sides
Ultrasonic clean
Check major power rails in diode mode

Stage 2: Main rail shorts

The first major short was:

PPBUS_AON short

Voltage injection and thermal camera testing showed:

CR604 and CR634 hot

After removing them, the PPBUS_AON short was cleared.

The second major short was:

PP5V_S2_UPC short

Voltage injection showed:

CF406 and CF506 hot

After removing them, the PP5V_S2_UPC short was cleared.

Stage 3: Corrosion rebuild

After short removal, no major rail short remained. We then replaced visibly corroded and high-risk components:

capacitors
resistors
small IC chips

This was necessary because even if a corroded component is not shorted at that exact moment, it can become unstable later under voltage, temperature or humidity.

Stage 4: UF400 / SN2012024 fault

After rebuilding the corroded area, the board was powered on for the first time.

The USB-C readings were:

Two ports: 5V / 0.23A rebooting
One UF400-related port: 5V / 0A

This pointed to a remaining USB-C controller-side fault. Under the microscope, slight corrosion was found on the balls under UF400 / SN2012024.

The chip was removed, reballed and reinstalled. After that, the MacBook powered on.

This makes sense because a BGA USB-C controller may look acceptable from the outside, but corrosion under the solder balls can break communication, create leakage, or stop the controller from waking correctly.

Stage 5: Left-side sound fault

After the MacBook booted, left-side sound was not working.

The audio section was then inspected and repaired. UR600, UR630 and UR660 were replaced. Corrosion was found after removing the chips, confirming that the fault was hidden underneath.

After replacing these ICs, the sound issue was fixed.

Stage 6: Lid angle sensor fault

The final functional fault was the lid / angle sensor. When closing the top case, the system did not go to sleep.

The angle sensor was replaced, and the lid sleep function returned to normal.

The board was ultrasonically cleaned again before final testing.

Repair Timeline

Step	Result
Customer reported water bottle leak and no power	Confirmed
USB-C meter test	Skipped because powering on was too risky
Removed back case	Top side looked clean
Removed board	Severe underside water damage found
First ultrasonic clean	Completed before electrical testing
No exact 2025 schematic	Used similar 820-02757 board view / schematic as reference
Diode-mode test	PPBUS_AON short found
Voltage injection on PPBUS_AON	CR604 and CR634 hot
Removed CR604 and CR634	PPBUS_AON short cleared
Diode-mode test	PP5V_S2_UPC short found
Voltage injection on PP5V_S2_UPC	CF406 and CF506 hot
Removed CF406 and CF506	PP5V_S2_UPC short cleared
Replaced corroded parts	25 capacitors, 5 resistors, 2 small IC chips
Power-on attempt	Two ports 5V / 0.23A rebooting, one port 5V / 0A
Microscope inspection	Corrosion under UF400 / SN2012024 balls
UF400 repair	Removed, reballed and reinstalled
Result	Mac powered on
Audio test	No sound on left side
Audio repair	UR600, UR630, UR660 replaced
Result	Sound fixed
Lid close test	Mac did not sleep
Sensor repair	Angle sensor replaced
Final cleaning	Ultrasonic clean again
Final result	Mac fully functional

Key Lesson

Severe water damage is often hidden. A MacBook logic board can look clean on the top side while the underside is badly corroded.

The most important lessons from this case are:

Do not power on a severely water-damaged board before inspection and cleaning.
A normal USB-C power test can make the damage worse.
Check major rails in diode mode first.
PPBUS_AON and PP5V_S2_UPC shorts were found before normal power was applied.
Use controlled voltage injection, not full power.
Injecting carefully allowed the thermal camera to locate CR604, CR634, CF406 and CF506 without powering the whole board.
A similar schematic is still useful when the exact one is unavailable.
It does not remove all guesswork, but it gives direction.
After the Mac boots, keep testing.
This board still had left-side sound and lid angle sensor faults after the no-power issue was fixed.

Final Fix

The final repair included:

full board removal and underside inspection;
ultrasonic cleaning before power-on;
diode-mode checks on major rails;
voltage injection and thermal-camera short finding;
CR604 and CR634 removed from PPBUS_AON short;
CF406 and CF506 removed from PP5V_S2_UPC short;
replacement of 25 capacitors, 5 resistors and 2 small IC chips;
UF400 / SN2012024 removed, reballed and reinstalled;
UR600, UR630 and UR660 replaced for left-side sound;
angle sensor replaced for lid sleep function;
second ultrasonic clean;
final functional testing.

Final result:

MacBook fully functional

If you are interested in the deeper diagnostic side of Mac repair, we have more real logic board fault cases documented here:
Mac Logic Board Repair Case Studies

If you have a water-damaged MacBook Pro, especially a newer model where Apple or another repairer has recommended main board replacement, contact IT-Tech Online before replacing the whole board.

We specialise in MacBook logic board repair in Melbourne, including severe water damage, no-power faults, USB-C power faults, shorted rails and board-level component repair.