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iMac Intel 27" EMC 2309 (Late 2009, Core 2 Duo 3.06 or 3.33 GHz) ID iMac10,1, EMC 2374 (Late 2009, Core i5 2.66 GHz or Core i7 2.8 GHz) ID iMac11,1

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How do you diagnose backlight fault on iMac logic board?

I'm trying to diagnose a backlight problem related to an iMac logic board.

Symptoms/Notes:

  • Boots fine but screen is black
  • Image can be seen when shining a torch on screen
  • External monitor works fine
  • All 4 diagnostic leds are lit

Other things:

  • LED invertor board is good
  • Power supply good
  • LCD and cables all good
  • Cable when plugged into LVDS connector has continuity through all 30 pins

So the problem definitely seems to be with the logic board but I'm not sure where, or how to test further. I don't know the history of the board but it does appear to possibly have had the cables janked upon opening at some point as the LCD temp sensor is ripped off.

The only thing I can think of is to replace the LVDS connector but upon close inspection all joints look good, all pins have continuity through a cable, and the correct pins are grounded.

Is there anything else I can test? any other known logic board components, fuses etc. related the backlight?

I've been trying to find some schematics but had no luck.

Answer this question I have this problem too

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It is a Core i5 iMac (2374)

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Shane Murphy I am sure that you already checked your diagnostic LED's but just forgot to mention it.

LED #1

• Indicates that the trickle voltage from the power supply has been detected by the main

logic board. This LED will remain ON whenever the iMac is connected to a working AC

power source. The LED will remain on even when the computer has been shut down or

put to sleep. The LED will turn off only if the AC power source is disconnected or the power

supply is faulty.

LED #2

• Indicates that the main logic board has detected proper power from the power supply

when the computer is turned on and that logic board voltage regulators are functioning

properly. This LED will be ON when the computer is turned on and the power supply is

working correctly.

LED #3

• Indicates that the computer and the video card are communicating. This LED will be ON

when the computer is communicating properly with the video card. If LEDs 1 and 2 are ON

and you heard the startup sound, but LED 3 is OFF, then the video card might be installed

incorrectly or need replacement.

LED #4

• Indicates that the computer and the LCD panel are communicating. This LED will be ON

when the computer is turned on and video signal is being generated. If the LED is ON and

there is no image on the display, then the LCD panel, the LED backlight board, or the cables between might be installed incorrectly or need replacement.

I'd check the backlight board first. Again this is a generic answer since you did not specify what model your iMac is.

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Thanks for info but yes I did already check the diagnostic LEDS… I did mention that all 4 LEDS light up correctly. I can also confirm the LCD panel, LED backlight board and cables are all known to be good.

The problem is definitely isolated to the logic board – the only thing I can think of is the LVDS connector on the board but I just wondered if there was any other (backlight related) components I can check on the board before trying to install a new LVDS connector?

It's a core i5 model (2374).

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what is the number on your board itself? 820-XXXX?

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Board number: 820-2733-A

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any news?I got the exact same problem!

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Shane Murphy will be eternally grateful.
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