Troubleshooting intermittent black screen on MacBook Pro M1 Max

Hey everyone,

I’m trying to get an accurate diagnosis of a screen/backlight issue on my MacBook Pro 16” M1 Max (Model A2485, Late 2021). I’m hoping someone can help me confirm the most likely failure point or suggest possible DIY or lower-cost repair alternatives before I commit to a full display replacement.

Symptoms:

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• Internal display is usually black.
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• Occasionally the screen flickers on briefly, especially after being connected to an external display and then reopening the lid.
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• At one point, I saw a yellow vertical line with red near the center of the screen. That line eventually disappeared, but the display hasn’t been stable since.
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• The screen is detected in System Information > Displays and via system_profiler, even when it isn’t displaying an image.
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• External monitors work perfectly.
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• There’s a dent behind the Apple logo, which I suspect may have damaged the T-CON board or internal sensor components.
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Diagnostics & Tests Performed:

Apple Diagnostics:

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• PPP020 – Power delivery or charging circuit issue (possibly related to the display power rail or boost IC)
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• NDC001 – Lid sensor or ambient light sensor failure
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Console Log Monitoring:

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• powerd logs show repeated entries like:
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• PID xxx is not entitled to set property AppliesOnLidClose
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  • DesktopMode check on Battery 0
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• SMC logs show constant errors:
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  • AppleSMCFamily::handleSMCResult ERROR in _readKeyGated – kSMCKeySizeMismatch(0x87) for keys like ATP0, ATC0, etc.
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• These suggest communication errors with internal sensors, likely tied to the display assembly or the lid sensor.
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Hardware Inspection:

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• Opened the MacBook and visually inspected display flex cables — no burn marks or physical damage.
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• Backlight fuse area looks clean (though I haven’t tested voltages yet — no multimeter on hand).
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• No liquid damage or corrosion.
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• Moving the lid at certain angles sometimes triggered the screen to flicker on briefly, supporting the idea of a cable strain or sensor failure.
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My Current Theory:

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• Either the T-CON board is damaged (possibly from the dent), or there’s a failure in the lid sensor circuit that’s keeping the backlight from activating.
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• Alternatively, there could be an intermittent backlight power rail issue (blown fuse, failing boost IC, or loose internal display flex near the hinge).
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• The vertical line that appeared briefly may suggest a deeper panel issue, though it hasn’t returned.
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What I’m Looking For:

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• Can anyone help confirm whether this is most likely a T-CON board issue, a lid sensor failure, or something else?
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• Are there known hall sensor replacement methods or diagnostics for the ambient sensor cable?
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• Would this require a full display replacement, or could it be repaired at the component level (backlight fuse, sensor line, or internal flex)?
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• Any reputable Canadian suppliers or shops for used OEM A2485 screens?
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• If anyone has attempted similar repairs, would appreciate any insight or teardown advice.
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Thanks in advance! Happy to upload more photos or logs if needed

[Re-Titled by Moderator]