ACMT Display & Video Troubleshooting 2 — Questions and Answers
Question 1: A MacBook's display has lines running vertically across the screen after a drop. What is the most likely cause?
- Corrupt GPU driver
- Cracked display panel or damaged LCD flex cable (Correct answer)
- NVRAM issue
- Incompatible macOS version
Correct answer: Cracked display panel or damaged LCD flex cable
Vertical lines on the display after physical impact almost always indicate a cracked LCD panel or a damaged flex cable rather than a software issue.
Question 2: What is 'image retention' on a Mac display, and how is it typically addressed?
- Pixels that are permanently dead; requires display replacement
- A temporary ghost image left on an LCD after displaying a static image; may clear with normal use or a display test (Correct answer)
- A GPU memory error requiring a logic board swap
- A macOS software rendering bug
Correct answer: A temporary ghost image left on an LCD after displaying a static image; may clear with normal use or a display test
Image retention is a temporary phenomenon where a ghost of a previous image lingers on the LCD; running a white or grey screen for several minutes often clears it.
Question 3: Which Apple tool allows a technician to adjust display color profiles and run uniformity tests on a replacement iMac display?
- AST 2 Display Diagnostics (Correct answer)
- ColorSync Utility
- Night Shift Settings
- Magnifier accessibility feature
Correct answer: AST 2 Display Diagnostics
AST 2 includes display diagnostic tests that check for backlight uniformity, color accuracy, and pixel defects following a display replacement on iMac and MacBook models.
Question 4: A MacBook Pro with a Retina display has bright white spots or 'blooming' around dark areas. What does this indicate?
- A software rendering issue
- Backlight bleed through the LCD layers, often from pressure or a failing display (Correct answer)
- GPU overheating
- Incorrect color profile
Correct answer: Backlight bleed through the LCD layers, often from pressure or a failing display
Backlight bleed is light from the LED backlight leaking around the edges or through the LCD panel, commonly caused by physical pressure or a degrading display assembly.
Question 5: After replacing a MacBook display assembly, the technician notices the ambient light sensor is no longer adjusting brightness. What was most likely missed?
- Auto-brightness was not enabled in System Settings
- The ambient light sensor cable was not reconnected during the display replacement (Correct answer)
- The GPU needs a firmware update
- SMC was not reset
Correct answer: The ambient light sensor cable was not reconnected during the display replacement
The ambient light sensor has its own cable that must be reconnected when replacing a MacBook display assembly; missing this step disables automatic brightness adjustment.
Question 6: What is the recommended procedure when a MacBook display has been replaced with an Apple-genuine part but True Tone is not working?
- Replace the display again
- Use AST 2 to run the True Tone calibration process which serializes the display to the Mac (Correct answer)
- Reset NVRAM
- Reinstall macOS
Correct answer: Use AST 2 to run the True Tone calibration process which serializes the display to the Mac
True Tone requires a calibration step in AST 2 after display replacement so the display's color sensors are matched and serialized to the specific Mac.
ACMT Display & Video Troubleshooting 2
A MacBook's display has lines running vertically across the screen after a drop.
What is the most likely cause?