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Quick Repair Summary

  • Device: 14-inch MacBook Pro M4 2024
  • Model: A3401
  • Logic board: 820-03400
  • Area: Northern suburbs VIC 3064
  • Original issue: Broken screen
  • New issue: No power after screen replacement
  • USB-C reading: 5V / 0.5A stable
  • Cause: Wrong-generation replacement screen damaged the board
  • Faulty area: Webcam / camera power circuit
  • Faulty chip: UD950
  • Repair: UD950 replaced
  • Result: MacBook powered on again

What We Found

Because the MacBook stopped working immediately after a screen replacement, we checked the screen connector and camera-related circuit first.

The replacement screen used the same physical connector, but that does not always mean it is safe to use.

On this newer M4 MacBook Pro, Apple changed the camera / webcam circuit design. Older M1–M3 style screens may look like they fit, but the pin wiring is not the same.

In this case, the replacement screen connected two pins together that should not be connected together on the M4 board.

820-02918 board view screenshot showing JP400 camera connector and selected PP5V_S2_CAMERA pins 29 and 30 used as reference for M4 screen connector diagnosis.
820-02918 board view reference showing JP400 camera connector pins 29 and 30 connected to PP5V_S2_CAMERA on the older design.

Why the Wrong Screen Caused No Power

The older screen design had two connector pins tied to the same 5V camera power rail.

But on the M4 board:

 
One pin is 5V
The other pin is 1.8V
 

The wrong screen effectively pushed 5V into a 1.8V circuit. That damaged the logic board and caused a short.

After the damage, the MacBook would not boot and stayed at 5V / 0.5A on the USB-C meter.

820-02918 schematic screenshot showing JP400 connector 20875-028E-01 with pins 29 and 30 connected to PP5V_S2_CAMERA.
Schematic reference for the older 820-02918 camera connector, where pins 29 and 30 are both tied to PP5V_S2_CAMERA.

How We Repaired It

We tested the damaged rail and found that one connector pin was shorted.

Then we carefully injected 1V into the shorted rail to find the damaged component. The faulty chip UD950 became hot, which confirmed the fault location.

After replacing UD950, the MacBook powered on and worked again.

Customer-friendly infographic showing a 14-inch MacBook Pro M4 that stopped powering on after wrong screen replacement, explaining how 5V was injected into a 1.8V camera circuit and repaired by replacing UD950.
This infographic explains how a wrong-generation replacement screen caused a 14-inch MacBook Pro M4 to stop powering on, and how board-level diagnosis found and repaired the damaged UD950 chip.

Why This Repair Matters

This case is a strong warning for newer MacBook screen replacements.

A screen can physically plug in and still be the wrong part electrically. On newer M4/M5 MacBooks, the webcam and sensor wiring can be different from older models.

Using the wrong screen can damage the logic board.

For screen replacement on newer MacBooks, the part must be checked by model and generation, not just by connector shape.

Final Result

After the repair:

  • the shorted rail was fixed;
  • UD950 was replaced;
  • the MacBook powered on again;
  • the original logic board was repaired;
  • the MacBook was working normally.

This repair shows one example of how we help customers recover their Mac instead of replacing it. See more completed Mac repair cases here:
Successful Mac Repair Cases

If your MacBook is stuck at 5V, keeps restarting, will not charge, or only some USB-C ports work, contact IT-Tech Online before replacing the whole logic board.

We provide professional MacBook USB-C charging repair and logic board repair in Melbourne, with mail-in service available across Australia.

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