Chosen Solution
I have a thunderbolt display that does not display a picture when connected nor does it come up in the settings, display window. However checking the system report it does recognize the display. It will allow me to select the camera on the display and audio will play through the display but not picture. I have replaced the function cable but no change. Would you goes lean towards the display or the logic board as the issue now? I have tried this display on a mac mini late 2012 and MacBook Pro Early 2011.
Take a flashlight placing it on the screen as a sharp angle to see if the faint image of your desktop and its icons are visible. If you do, your backlight logic need repairs. If not, then the GPU logic needs attention on the logic board. I would recommend you start things by testing the logic board power feeds to make sure they are at the correct voltage. Update (10/06/2018) OK, heres the test points and the voltages you’ll need to see on the logic board power connector:
Pins 1 & 7 PP24V_S5_PREFILT «< 24 Volts Pins 2 & 8 GND_ACCD24 «< Common Pins 3, 4, 9 & 10 DC_12VIN neg «< 12 Volts Pins 5 & 11 DC_12VIN pos «< 12 Volts Pin 6 FAN_ON_IN_L Pin 12 NC_DCIN
Adding onto @danj ‘s solution (respectively mark his answer as correct if you do decide to mark an answer as correct), this appears to be a Logic Board problem because as Dan said you are getting voltage to the Logic Board. You can buy a new Logic Board at the link below. There isn’t a specific guide on how to replace the Logic Board, but you can follow the guide I have included below also. Just disconnect any other cables that need to be disconnected at step 19 and you should be golden. Apple Thunderbolt Display Thunderbolt & MagSafe Cable Replacement https://www.macpalace.com/661-6060-logic…
I have a similar situation where everything works (speakers, camera, and even video passthrough to another monitor), except the backlight (I can see the faint image with a flashlight) Justin’s earlier response indicated the backlight logic likely needing repair. What would be the next steps?
sorry to dig this up-my monitor backlight isn’t working…I’ve measured my voltages as above, everything except no reading from pins 5 & 11 -these should be + 12v, right? I’ve tried 3 different PSU boards and all yield the same result, should I now be looking at the logic board or controller board? any thoughts would be most welcome! thanks.
