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対象のモデルはA1419 / EMC 2806 / Late 2014 または Mid 2015。 3.3 または 3.5GHz Core i5 または 4.0GHz Core i7 (機種ID iMac15,1)、EMC 2834 late 2015 / 3.3 または 3.5 GHz Core i5 または 4.0 GHz Core i7 (機種ID iMac17,1)のRetina 5Kディスプレイを搭載したすべて。

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iMac won`t power on. Power button pressed = LED # 2 lights up briefly

Hey Guys

I currently have an iMac 27 "5K Late 2015.

The iMac will not turn on.

Diagnostic LED # 1 lights up when the Mac is powered.

As soon as the power button is pressed, LED # 2 lights up briefly and goes off again.

There are no fans running.

Power supply is fine.

Someone an idea?

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Do you have a good surge suppressor or UPS for your system and its peripherals ? It sounds like you had a surge event that got to your logic board. This could be from the AC line cord, Ethernet network connection or the USB & Thunderbolt ports.

さんによる

I have a similar problem, but in my case the diagnostic lights won't even come on! The PSU seems to be working. I measure 120v in the AC inlet. And when I test the 12v lines (there's two of them, and two grounds), it measures at a health 12.xxx volts.

I also tested the power button, when pressed the resistance across the power button cable drops to 0.

I did swap my CPU, could this be causing the issue? (diagnostic lights not coming on?).

さんによる

Hey So i had this issue and it was driving me crazy, i replaced the psu still nothing, then i put the psu in a known working imac and it powered on normal. i started playng with everything until i took all the ram out and put just one in. Bam! started. so i put all the sticks back in and it was working normally. I think one or two were maybe not connected properly.

さんによる

Hello my iMac 2011 was doing exactly the same thing. I took the screen out right back to the button check the button everything was ok check the connection back to the logic board, all was ok I took half of the RAM out, there was four sticks in ,and powered it back up this time the number one LED that was going out as soon as I pressed the power button stayed on. The 2 nd LED stayed on and then the familiar bing bong and my iMac came back to life. Thanks for the tip. I wish I had tried taking out the ram first.

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Here's the on-board Diagnostic LED info for reference. 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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so has anyone gotten a led 1 turn off after pressing the power button and figured out a fix?

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i have the same problem, Led 1 ON, when pressing the PowerButton the Led1 OFF and i have to disconnect main power cable from power source, wait and try again, 1 of 10 tries im able to turn on the PC.

Tomarrow i will try to remove the ram. sticks

さんによる

Same thing!

Led 1 is solid. Pressing the power button does nothing and led1 goes out.

Sometimes by pulling out / reinserting the RAM, imac starts normal and everything works. But this happens just once. After shutdown it wont boot again

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Sorry this is not an answer, but I have the same problem. I get no display and no chime when powering up. I have it on a wired keyboard and I don’t get any lights turning on the keyboard.

I removed the display panel and I get LED 1 and 2 lighting up but 3 is not and 4 is not.

  • I can hear the fan going faintly.
  • I get the beep when testing with ram chip removed from board.
  • I also did another test (forgot what I did, read online somewhere) that made my fans go on high speed…. not sure what the test was for lol.
  • I already tried changing the coin battery just to see if it’ll help but still nothing.

What could possibly be a fix for me?

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Have you figured out the issue Roy? I have the same symptoms.

さんによる

i think its a screen issue

さんによる

Did you find a fix? I have the same issue.

さんによる

Any update yet i have the same issue here thanks

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Sorry to open up an old thread but any ideas to my issue. Firstly LED 1 would flash up and go off when power pressed. Suspected power supply, replaced but no difference . Sent PSU back. Ordered logic board. Logic board fitted and now when power lead plugged in LED 1 flashes and when I press the power button it flashes quicker…. I am now VERY confused. Could it be PSU AND Logic board failed?

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One question: did you replace the CPU as well, when replacing the logic board? Or the CPU is still the same?

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Okay… I have 2 units having the same issue. Replaced the PSU didn’t work, replaced this and that also didn’t work. I replaced the clock battery, voila! It works! But… not the other iMac. The other iMac is still holding mystery issue. Argh!!!

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I had the same problem. I had a bad hard drive and replaced it. As soon as I put it back together, the system wouldn't power on. LED1 stayed on and LED2 would blink once every few seconds after I hit the power button.

After trying a new power supply with no luck, it ended up being an issue with the RAM. I wasn't getting POST beeps, but the RAM was definitely the cause of the problem. Check each RAM stick individually in the iMac and see if it powers on.

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in my case it was the Logicboard

さんによる

ouch, sorry to hear that.

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I have the same issues! iMac late 2015 27inch! Only diagnose led 1,2 work 3,4 won’t! No screen only fan working when I turn on! Help

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Did you fix it?? I have the same problem

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I had an experience that may worth sharing.

I upgraded my iMac 2011 with a dual HD with SSD from OWC. It worked for about a week and one morning I woke up with a dead iMac. I opened it up and found only LED1 lit up. I follow the trouble shooting and fortunately I have a similar model that I was working on, so I replaced the PSU, the cable, the GPU, and even the logic board with no avail. I finally checked the last change I made to the computer which is the new SSD. So I unplugged it and all 3 LED lit up.

I took out the SSD and hooked up to other computer and it reported USB device was disabled because it consume too much power.

So, my worth check the HDD out if LED2 can’t light up.

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I have a iMac 27 2019 base model, it doesnt start, I have only led 2 green and blinks when push the power button. Any idea?

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golffreiburg さん、ありがとうございました!
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