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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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No Disply but Diagnostic Led 3 & 4

Please assist.

iMac suddenly do not display after trying to install firmware update(vid was flickering). Initially suspect video card, after tear down, both LED 3 & 4 are the only ones ON even though Mac turns on (Fan included) and you can hear the chime.

Any input on whats possibly the issue? Logic board?

Answer this question I have this problem too

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  1. Try connecting to an external monitor. You may see an image there. Can you provide a link to the EFI update you used (or at least state the version), and a reason why you felt you needed to install it?
  2. LED #3 is normally "on" when all is well.... LED #4 indicates an overtenp problem (but due to the EFI screw up that might be a false reading).

# Try booting to your AHT diagnostic disk or partition.

  1. Try a safe (shift) boot.

If this answer is acceptable please remember to return and mark it.

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