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On my A1502 if i connect to hdmi i can see video and computer works fine. Some times the lcd will come on then shut off within a few seconds. I dissasembled the screen and check the display cable. It looks ok. Anything else i should check?
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Well, that clearly points to a connector or logic board issue.
Carefully inspect the solder joints of the display connector look for a cold solder joint. If you have the skills I would resolder the connector.
You’ll need the get the schematics and boardview drawings and trace out the backlight logic.
Here’s a block diagram to help explain things
Here the MUX logic sends a signal to the PCH to disable the the internal display when the lid is closed via the Hall Sensor.
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I have a boardview of this mobo, Also the laptop has not been dropped it just went out one day. Is there a way to bypass the hall sensor to see if that is the issue?
@Dan - you could try a magnet passing over the uppercase where the ports are to see if you can toggle it on and off.
I tried it with several strong magnets and nothing.
@Dan - At this point you'll need to get the schematics and boardview drawings to trace out the logic.
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When the screen is black shine a flashlight though the lids Apple logo acting as a backlight. Are you able to see the faint images of your desktop and its icons?
by DanJ
Sorry i should of said that. I tried that and no image. I checked the backlight caps and no 48V. I also wanted to note that there is no water damage on this. Also that inductor by the lvds connector has 0V as well.
by Dan
Slight correction the connection is not LVDS any more (unibody) its iDP signaling used in the retina models (early versions it was called eDP). Similar cable but different just the same.
by DanJ
@Dan No backlight and no image but external monitor works? Sounds like a firmware problem. Did this happen out of the blue?
by Chris Stables
@imicrosoldering - Why would you think this was a firmware issue?
Remember the 13" Retina systems use the CPU's intergraded graphics engine (no discreet GPU). So the data from the GPU is the same for the internal and external displays. This is likely a MUX logic issue. But we should first make sure the simpler issue is removed (bad connection)
by DanJ
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