No backlight on external display

This one is throwing me for a loop.

Late 2009 MacBook connected to an external DVI display via DVI cable and DVI -> mini Displayport / Thunderbolt adapter. The MacBook's built in display operates with no issue but the external display gets backlight for 2 -3 seconds then goes dark, though video is still available if you shine a light on the display.

Issue has persisted across two different displays (one Samsung, one Viewsonic), with two different DVI cables, two different power cables for the displays and two different DVI adapters. Both displays worked properly with a known good Mac so I really doubt they are to blame.

I've done the following with no change in performance:

  • Reset SMC
  • Reset PRAM
  • Reset NVRAM
  • Safe Boot
  • Booted to KG OS on external drive

At this point I'm ready to call it a bad logic board but with the Mac being out of warranty I want to make sure I'm exhausting all options. I've never seen this particular issue before but would be more accepting of it if I knew others have run into it.

Any ideas? Any similar experiences?

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Have you tried, in Display, changing the refresh rate of the external monitors? You might be sending them a rate they can't maintain.


Meant to mention that, I have. Tried changing both refresh rate and resolutions, no change. Also tried in closed clamshell mode, still no change.


Occam's razor - aka: KISS I agree with your assessment.


Like ARabbit, you have the tools to check some components? just reviewed the schematic for your logic board, I'd check the RCLAMP0524P which is a Ultra Low Capacitance TVS Arrays to protect the display. Check the datasheet on here


Can you check out a second external display and/or try a different system with the same cables to this display to see if the display and/or cable setup could be at fault. Who's external display are you using?


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