iMac does not boot up Led 4 on mother board only
the only thing that powers on is the hard drive and I only have led 4 on the mother board, Ive already change the power supply but no change.
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Here's the on-board Diagnostic LED info for reference. Your logic board appears to have issues not your power supply. Can you give us a bit more on what happened with your system.
Diagnostic LEDs
LED 1 - Indicates that the trickle voltage from the power supply has been detected by the main logic board. This LED will turn on when you connect the iMac to a working AC power source. The LED will remain on as long as the computer is on or asleep.
When the computer has been shut down correctly, LED 1 behavior may differ:
If a startup event is scheduled in System Preferences/Energy Saver, LED 1 will stay on after a correct shutdown. If no startup event is scheduled in System Preferences/Energy Saver, LED 1 will turn off and will stay off as long as the power cord is kept connected and an AC power source is present. Disconnecting the power cord and plugging it back in will turn this LED back on, even if the computer is still off.
After disconnecting and reconnecting the AC power source, this LED could remain off: If the AC power source is missing or disconnected.
If the logic board is disconnected from the power supply or the AC receptacle.
If the power supply board is faulty.
LED 2 - Indicates that the computer is turned on. This LED will be on as long as the computer is turned on (but is not asleep) and the power supply and voltage regulators are working correctly.
LED 3 - Indicates that the computer and 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, the backup battery (on back of logic board) may need to be reseated or the video card might be installed incorrectly or need replacement.
LED 4 - Indicates that the computer and LCD panel are communicating. This LED will be ON when the computer is turned on and a video signal is being generated. If LED 4 is on and there is no image on the display, the LCD panel or the cables between the LCD and logic board might be installed incorrectly or need replacement.
LED Startup Sequence
LED 1 = Power is available.
- If no LED is visible:
- Disconnect the power cord from the computer and wait 15 seconds to reset the power supply and LED status. Reconnect the power cord and check the LED status again.
- Verify the AC source.
- Verify that a known-good power cord is connected.
- Verify the cable connection between the AC inlet and the power supply. Verify the cable connection between the power supply and the logic board. Verify the power supply.
LED 1 + LED 2 = Power is available and the system is turned on. If the second LED is not visible when the power button is pressed:
- Verify that the power button is connected to the power supply.
- Verify power button functionality.
- Verify the cable connection between the power supply and the logic board. Verify the power supply.
- Verify the logic board.
LED 1 + LED 2 + LED 3 = Power is available, the system is turned on, and the GPU was found.
- If the third LED is not visible after the system is turned on:
- Verify whether the boot chime is present and fans are running when turned on (reset the SMC and PRAM and verify backup battery voltage for proper startup).
- If the POST boot chime is not heard, go to the No Startup symptom flow. If the POST boot chime is heard, go to the No Video symptom flow.
LED 1 + LED 2 + LED 3 + LED 4 = Power is available, the system is turned on, the logic board is communicating with the GPU, and the internal LCD was found.
- If the fourth LED is not visible after the system is turned on:
- Verify the internal DisplayPort cable (eDP) connections between the LCD panel and the logic board. Inspect the LCD display cables for cable damage.
- Verify external video functionality and proceed according to the result:
- If an external display works, verify/replace the LCD panel.
- If an external display does not work, verify/replace the logic board.
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does Apple not have an answer for led 4 on only nothing in the service manuel explains whats wrong when its on led 4 on and the drive works.
Check on everything above still no change
Please give us some background info what happened before it stopped working.
This is all there is so you have a really messed up logic board if only #4 LED is lit. Are you sure you haven't reversed the order. Apple doesn't make note in the manual what the order is of the LED's so I'm thinking the bottom one maybe #1 here which would make more sense.
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If you have power and no beeping sounds but no image on the screen then it is possible a GPU issue. It seems the gpu on this model is soldered onto the logic board. You can send it off to have the logic board reballed or you can replace the logic board.
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if the mother board responds when you place the wrong kind of drive in it would that not say the board is working?
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In my case (iMac late 2012, A1418, i5 2.9GHz) LED 1 + LED 2 + LED 3 is ON, LED 4 is OFF when is display connected on board. When then connect adapter miniDP-HDMI on TV, just black screen on TV. When disconnected iMac's LCD then I have image from iMac on the TV, but internal fan in iMac is loud (because temp.sensor on LCD). Still, LED 4 is OFF. I was inspected the LCD display cable and motherboard but no visible damage. I'm confused...
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@Zeljko Devic - Without knowing what lead up with the systems current state its hard to tell what needs deeper inspection or replacement.
Whats the background: Where you upgrading or did it just stop working?
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@galipeau you have verified that this is LED 4 and not LED 1? LED 4 will be ON when the computer is turned on and a video signal is being generated. That implies that your computers power supply etc. would be functioning as well. Therefore at least #1 and #2 LED would be on as well.
da oldturkey03
LED 123 are off it was rebooting and just stoped .
da Denis Gregoire
@oldturkey03 - I haven't needed to diagnose one of these using the LED's yet.
I do have the manual and it doesn't make note of the order of the LED's. I looked a bit online I don't see anything other than the older systems.
I'm thinking Apple has the bottom one set as #1 If one twists ones head to the left then that would read from left to right 1 > 4. Besides the fact #1 needs to be lit suggests this is then the order.
da Dan
@galipeau post a couple of images of your diagnostic LED's and point out which one you find to be lit. Aggiungere immagini ad una domanda
da oldturkey03
Ok I will add photo of the led though top to bottom it’s the bottom last light
da Denis Gregoire
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