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

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LED power supply and logic board tests

My 2210 iMac won't power up, so I have taken it apart, following the ifixit instructions for power supply removal. I don't see anything inside that is obviously broken or burnt out. I am told by a Mac repairman that it is probably either a bad logic board or power supply. How can I test my power supply and/or logic board to see if they are functional? Thanks.

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I have my iMac it has another issue my guts say its the power supply.

First led stays on the rest of the leds don't light up. I can hear the hard drive loading iMac shows no sign of any fan spin and no screen and no chime.

Anybody having this experience or suggestions?

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Plug the power supply back in and check the diagnostics lights on the logic board.

For the G5 not for Intel

LED 1 indicates that trickle voltage from the power supply has been detected. This LED will be ON when the computer is turned off and your power supply is working correctly.

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 LCD display are communicating. This LED will be ON when the computer is turned on and video signal is being generated.

LED 4 lights only if the computer detects an over-temperature condition. This LED will be OFF when the computer is turned on and running at the correct temperature.

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Where on the logic board are these LEDs? maybe I'm not seeing them because my power supply is dead?

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The LEDs are to the right of the memory slots, and sit behind the SATA cable where it comes out of the connector.

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The LEDs I listed are for the iMac G5 not the Intel model.

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myimac 21.5 and led 4 is off then whats the problem logic board or display

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What about if none of the LEDs are ON?

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Um.. doesn't LED 4 on this model denote the LCD comms status?

2007/8 models

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.

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I think I copied my answer directly from Apple. Yours appears very close and may be a revision. Care to give a link?

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I took mine from the 2007 service manual. The info you gave matches with the iMac G5 and is the only reference I can find on apple.com about diagnostic LED's

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FWIW the Diag LED's are not present in early 2006 model and reappear in the Late 06 model

LED #1

Indicates that the trickle voltage from the PSU has been detected by the logic board. This LED will remain ON whenever the iMac is connected to working AC power. 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 PSU is faulty.

LED #2

Indicates that the main logic board has detected proper power from the PSU when the computer is turned on. This LED will be ON when the computer is turned on and the PSU is working OK.

LED #3

Indicates that the computer and the LCD are communicating. This LED will be ON when the computer is turned on and video signal is being generated.

Front LED

Indicates that the computer has power but no video signal (e.g., the computer is starting up or the display has entered Sleep mode, turning off the video signal). This LED will pulse when the entire system enters Energy Saver mode

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+ vote for the research, I tagged it and changed the title so it can be found again. Nice work.

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FYI - From the 2009 21.5/27 inch service manual

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

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iMac Intel 20" EMC 2133 and 2210

No display at all, LED 4 is OFF when Computer is ON !

I removed the LCD and check it with another iMac and found LCD is working fine, what should I do next? thanks in advance

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Hi,

When none of the LED's are lit, this means there is no power at all, and one would suspect the power supply.

Don't jump to conclusions too fast, however, and check the AC input connector, mains filter and AC wiring to the PS board. If you know how to handle a multimeter, check the mains voltage on the PS board. You can also unplug the connector to the logic board, and see if you have the tricle (stand-by) voltage (about 2,5 V DC).

Be aware that a power supply has protective circuits on the main output voltage line (12VDC). When there is a short circuit in the logic board (or audio board, video card etc), you won't be able to start the computer (LEDS 2/3 remain dark) but you can have the trickle voltage. I was fooled once by this situation, thinking of 'only' a defective PS, but when I pulled out the video card my iMac came back to life !

I don't know if the trickle voltage line is protected (guess not).

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how can the iMac come back to life without a video card?

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----

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

-----

All above verified.

May I be shure I have to replace the power supply, or could it be something else ?

Update

Question: how can I have 10 results while first solder is the reference?

Here are my 9 results :

1: n/a

2: 1.1

3: 0

4: 2.5

5: 2.6

6: 0

7: 46

8: 37

9: 12.3

10: 0

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Thanks. I've seen that page, but the following warning :

* Should only be attempted by those with experience working with a multimeter or voltmeter and LIVE equipment.

* If you don't know how to use a meter to measure voltages then you should not proceed.

made me stop...

I do use a multimeter sometimes, but only to verify continuity.

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So... I decided to try to do the PSU test.

I was writing the first mesure (1.1 mV) when I heard a big CLAC ! coming from the iMac.

I unpluged the machine.

With that information, can I now infer that I have to change the power supply ?

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If all measurements are mV then I'd say yes the PSU is faulty. If the measurements are VOLTS then the PSU is also faulty but the main board could well be damaged with those voltages applied. Remember that the PSU may have damaged other components when it failed or could have failed due to a faulty component somewhere else.

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Hi all. I have an 20" imac 2133 and yesterday after a short circuit in my house imac dropped dead. I choosed to open my imac since i got no money (see economic crisis - Greece). Found 2 burned part on PSU a T4A fuse and a 420V 150uF Capacitor. I will change them and if i got good news I will post...

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Mid 2007 IMAC 24"

My experience: I had 3 of 4 LED lights lit on a dead, no start up, no chime, no fan Imac. Problem solved when new power supply was installed.

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Hi friend, Your model is 24” a1225 emc2211? I have exactly the same problem...

According to the led test it is a problem of the connection of the display or the video card, but I am almost sure that it is power supply ...

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Hi there , i have a issue with a a1224 , powers up everything works correctly, but the 4 th led stays on.. and i have no back light for the lcd .. if i use a flashlight i can see on the display.. what can i do ? :(

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backlight inverter needs replacing, or possibly the backlight fluro tube in the screen needs replacing... which would usually mean replacing the entire panel.

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mycoloco さん、ありがとうございました!
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