Model A1224 / Mid 2007 and Early 2008 / 2, 2.4, or 2.66 GHz Core 2 Duo processor

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How to determine what is defect if the system doesn't post?

iMac 20" (MB417)

I have following symptom on an iMac on power-on:

- black screen

- drive briefly spins

- system powers off within 1-2sec.

What is the most likely cause and how can this be tested?

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按维修分数 1


There's really not enough information to give you a diagnosis yet. Can you give us a history of the problems you've had with this machine. What were the symptoms at the onset of this problem?

Unfortunately there is not much more to say.

Pressing the power button gives the above effect. You hear the HD spinning up and the Superdrive initializing. Than it simply powers off again by itself. The screen just stays black.

Only thing I can add as history is that the system run 24x7 as file and print server for a small workgroup.

Its unclear why it switched off in the first place. Fact is that it no longer switches on :-(

I had it repaired. Initially they only changed the logicboard, than, after it happened again the next day, also the powersupply was replaced. I was told the SMC on the logic-board was defect. Does that make sense?

It means they had no idea of what the problem was and tried to baffle you with BS. Does it work?




This may take some trial and error to find the problem. Resetting the SMC - First unplug the unit and press the start button for 5 seconds. Next try a PRAM reset, hit the start button and immediately hold down the Option & Command and P and R keys wait till you hear it tone three times. Next re-seat the RAM, here's how: iMac Intel 20" EMC 2133 and 2210 RAM Replacement

This failing you will need to open it and examine the diagnostic LEDs:

Here's a video on how to open it up:

You will need suction cups:

and a Torx screwdriver set, here's what I use:

LED Startup Sequence

LED #1 = Power available.

If no LED is visible:

• Verify AC source

• Verify known-good AC cable is connected

• Verify cable connection between AC inlet and power supply

• Verify cable connection between power supply and logic board

• Verify power supply

LED #1 + LED #2 = Power available, and system is powered on.

If second LED is not visible when power button is pressed:

• Verify power button connection to logic board

• Verify power button functionality

• Verify cable connection between power supply and logic board

• Verify power supply

• Verify logic board

LED #1 + LED #2 + LED #3 = Power available, system is powered on, and video card found.

If third LED is not visible after power on:

• Verify that MXM video card is seated properly

• Verify logic board

LED #1 + LED #2 + LED #3 + LED #4 = Power available, system is powered on, video card found, and internal LCD found.

If fourth LED is not visible after power on:

• Verify cable connections between LCD panel and logic board

• Inspect LCD display cables for cable damage

• Verify external video functionality, and according to result check the following items:

-If external display works then verify/replace LED backlight board

-If external display works then verify/replace LCD panel

-If external display does not work verify/replace logic board


按维修分数 7


I think I have to start bookmarking your answers for later reference..!

Nice + Ralph

Thx for the detailed answers! Unfortuonately no change with (trying) to reset SMC/PRAM. Its simply powering off before anything beeps... i don't have spare ram. How likely is it that the ram is causing the system to power off almost immidiately after it is swiched on? If i take out the ram, should it than show the same symptom?

It's not likely the RAM but it's worth a ret. Remove one at a time, try each stick in each slot to test both the slots and each stick.


Update: Do what mayer said first

  1. Try booting from your boot dvd (press and hold C to boot from dvd)
    • Did it work?
      • Yes? You probably have a software problem, use your dvd to repair or do a fresh install. If your HDD don't show up, your HDD is dead.
      • No? You probably have a hardware problem


Your problem could be anything..

I would personally start with ther ram. Depending on how much ram you have you can try to remove one of them and boot from the HDD, if it works the ram you removed is dead.

If you have spare ram laying around I would replace both in your machine and try to boot.

Try this and let us know what you found.


按维修分数 0

OK, I went through these steps. Three LEDs lit, external monitor works, but screen completely black. Found a deal on a used screen, swapped it out. Power up the Mac, the screen lit up long enough to show the apple on a grey background then died, now same symptoms as before.

Did I just kill another screen?

What next, logic board, power supply or inverter?

Should the logic board detect the panel even if the inverter and backlight isn't working?


Steve L.


按维修分数 0

omg I need answers to this...I have the imac 20" 2.4Ghz 2008 model...I need to know what is next as steve asked...thank you guys


按维修分数 0


well...I got a new video card and it still only showed the first two lights so I am assuming it's the logic board...don't know when I will be able to afford to get it I'm waiting till money comes in

I want to make this work...I'm just stressed about it


Thanks for the update - mine is sitting in a box in the basement. I was afraid it was the logic board which is why I haven't done anything. I'm not sure it's worth it to me to replace the logic board, I'd rather save the money towards a new mac, even a refurb or used one. I have another identical iMac, so it makes sense for me to save the parts in case that one starts to die.




I tried replacing the power supply with no luck. A friend of mine has a G5 iMac with the same symptoms, 3 of 4 diagnostic LEDs lit and for some reason he needed to replace the logic board.

So, now I'm deciding between Video Card, Power Supply or the recycling program. Fortunately I do not have an urgent need for this machine.



按维修分数 0


Steve, to avoid confusion please start your own question so we can give you individual attention.



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