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27" display with 2560 x 1440 pixels resolution Thunderbolt & MagSafe cable attachments

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No Display but Sound and Camera are Working

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.

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Solución Elegida

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:

Block Image

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

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Thank you for the reply. There is defiantly no image on the screen, nor does either computer give me an option to extend my display or duplicate to the thunderbolt display.

Is this one you recommend and are there others:

Verify voltage on logic board between test point TP81 (24.5VDC) and chassis ground (GND) is 23.3–25.7 VDC.

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Finally was able to test the pins with my multimeter, see values below:

PIN 1 - 25 PIN 7 - 25

PIN 2 – 0 PIN 8 - 0

PIN 3 – 12.15 PIN 4 – 12.15

PIN 9 – 12.15 PIN 10 – 12.15

PIN 5 - 0 PIN 11 - 0

PIN 6 - 42.7

PIN 12 – no good reading, all over the map, but positive voltage

Testing was performed with power on but display disconnected. Let me know what you think of these results.

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Sadly, it looks like the logicboard has a problem as you are getting voltage to it.

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Well bad news, installed the new logic board tonight and the laptop recognizes the diplsay now in the dispaly settings (so thats a plus) but the backlight is not working at all. I can faintly see the display when I mirror the screen and shine a flash light on it. With this new discovery could you please recommend the steps for the backlight logic repairs? Thanks!

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mmm.... Well you either got a bum board where the LED driver logic is damaged. Or the LVDS cable between the logic board and the display is bad as it carries the power to the LCD. There are a few fuse links in the circuit and there might be a few on the logic board on the back of the LCD.

It's starting to sound like your system got a good zap either a power surge or a lightning hit which could have traveled into your system via the power cord, other devices connected to your system and even the network connections.

I would strongly recommend you get a good surge suppressor for your system and any inter-connected devices. If you can swing it I would recommend a good UPS.

Even living in the city power and lightning is still a risk. I have four UPS's and a few surge suppressors for all my gear (and yes, I'm paranoid! As I've learned the hard way).

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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...

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Thank you for the guide and link. I was wondering if there is any difference between the part numbers 661-6489 and 661-6060? Do I need to remove my board first and check the part number?

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@justsmurph You might want to check your current board first and order the part number that your existing board has. That is what I would do, as these parts seem to be idenitical.

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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?

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You'll need to find the schematics and board view for your displays logic board and using a DVM check the LED driver logic and the feeds to the display.

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Thanks, found a Apple Technician Guide online and it includes directions to verify cables, check voltage on specific test points. It seems that is either the power supply, a cable or the logic board.

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Justin estará eternamente agradecido.
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