Model A1225 / Mid 2007 and Early 2008 / 2.4, 2.8, or 3.06 GHz Core 2 Duo processor

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Blank screen, no chime at start up

Out of no where, iMac 24" EMC 2134 (mid 2008) will not boot, no chime. I can hear fans power on, etc. I do not have suction cups at the moment, but was bale to peek inside the bottom where the vent holes are. Upon connecting power cable, first LED comes on. Upon start up, second LED comes on. There is a single flicker on the third LED, however, it stops there.

If I have deduced correctly from the LED descriptions, this indicates a video card issue. Am I correct?

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Jen Robinson, "

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 (24-inch) 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. 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 display 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 LCD display panel, the LCD display panel or inverter might be installed incorrectly or need replacement.

No Video, No Boot Chime

The computer will turn on, but there is no boot chime and no video on the display. The faint sound of the fans, hard drive, and optical drive may also be heard.

1. Make sure all software updates have been applied to the computer. Refer to KBase article 303903, Intel-based iMac: Installing available updates , and to Apple Downloads for updates for the iMac (Mid 2007) model of computers.

2. Follow instructions in the “General Information” chapter to reset the SMC. Does the computer display video after successfully resetting the SMC?

Yes: Problem solved.

No: Continue to next step.

3. Verify that only supported SDRAM memory has been installed and that it has been installed correctly. Unsupported and/or defective memory can prevent the computer from booting. It may be necessary to install known good memory for testing purposes and replace any unsupported or defective SO-DIMM’s identified during this process. Does the computer display video after verifying and/or replacing the memory with known good memory?

Yes: Problem solved. Verify full system functionality before return the system to the customer.

No: Replace the logic board.

5. Make sure the machine is powered off, and remove the access door and front bezel to access the diagnostic LEDs. Plug in and start up the computer to observe the diagnostic LEDs. At this point in the Power On process, you should hear a boot chime, and LED #1 and #2 are On. Is LED #3 On or Off?

LED # 3 is On: The video card and logic board are communicating properly. Go to the next step.

LED # 3 is Off: The video card and logic board are not communicating. Replace the video card. If the issue persists, replace the main logic board. Hope this helps, good luck.

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Did you forget about the PRAM reset?? Don't recommend that people replace their logic boards or video cards before they try that first! The PRAM reset worked perfectly for me and others I've recommended it to; it is not as well known as the SMC reset. In my case it would boot into a black screen with no chime at all. I nearly gave up until I came across the PRAM reset hint.

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Not necessarily -see Faulty iMac - Only three LEDs appearing in diagnotics?

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

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I should have worded more clearly. The third LED flickers once, then stays off. The link you provided covers if the third LED stays on. Mine does not. Thanks!

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Don't run out and buy a new logic board or video card just yet!! RESET YOUR PRAM!! (This is not the same as SMC reset)

As a potential solution to the black screen on boot, this is done upon restarting the Mac similar to an SMC reset:

Reboot the Mac and as soon as you hear the boot chime, hold down the Command+Option+P+R keys together

When you hear the boot sound again, the PRAM has been reset so let the Mac boot again as usual

At this point your Mac should boot again as usual and no longer have the black display, loading OS X as usual.

If there is no boot chime, don't worry, just hold down the Command+Option+P+R keys together shortly after you hear the typical boot up disc check, or within a couple of seconds of depressing the power button to turn on the Mac.

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Hello I have I think a 2008 iMac powers on I can hear fans but nothing else and screen stays black? So is it video card that went out?

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Hello! I press the power button and the 3 LED lights come on and the disc input makes sound but that is it. What should I try next?

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