MacBook Pro A2251 no camera detected repair

Problem description
Addressing issues with a MacBook (820-01949) not detecting the camera.

Symptoms

 * Camera not detected
 * Possible burned or exploded L8504 filter on TCON board

Check L8504 Continuity:

 * Use a multimeter in continuity mode to check L8504 (Figure 1).
 * Normal reading should be close to 0.01.
 * If L8504 is blown or burned, proceed to the "L8504 blown or visibly burned repair steps" below.

Test with Known Good Display:

 * Verify camera function using a KNOWN GOOD display assembly.
 * If the camera works with a different display, the original display might be faulty.
 * Make sure to check L8504 before diagnosing the display issue.

Camera Works with Known Good Display:

 * If camera works with a known good test display, replace the display assembly.

L8504 Blown or Visibly Burned:

 * Understand that L8504 failure indicates a catastrophic short within the TCON board of the display or a melted/corroded display cable/connector.
 * Repair L8504 only after addressing the display issue, as L8504 might fail again if the display issue persists.
 * When replacing L8504, address corresponding pad and trace damage.
 * Use 36 or 37 AWG enamel coated copper wire for jumper wires due to webcam and ambient light sensor power requirements.
 * Connect jumper wire from the input side of the filter (PP5v_G3S) to R5610 (Figure 2) or a suitable point.
 * Apply conformal coating to jumper wire.
 * Use a 120 Ohm ferrite filter rated for 1.5 amps (402 package size).
 * After replacing L8504 and addressing trace issues, replace the display assembly or repair it by replacing damaged cables/connectors.

No Camera Function, L8504 Normal:

 * Attempt to restore T2/BridgeOs firmware via Apple Configurator 2 by entering DFU mode.
 * Ensure your Mac is on the latest macOS version.
 * Follow Apple's support article on reviving or restoring T2/BridgeOs firmware.
 * If no camera function after firmware revive, and other causes are ruled out, U8504 might be faulty, or there could be trace/resistor issues between the camera connector/U8504 or between U8504 and the T2 chip.
 * A hardware issue with the T2 chip might also cause camera detection problems.