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Model A1418 / Late 2013 / 2.7 & 2.9 GHz Core i5 or 3.1 GHz Core i7 Processor

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No power on, No LED on logic board

Hey guys, Today I need your help!

I have an iMac late 2013 with 11.7 Volt of Logicboard (J600 plug) .

No diagnostic LEDs. System no Start

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I still have to measure other small plugs.

does one have a tip? O_o.

System :

iMac A1418 (21.5 Zoll) ME087D/A (late, 2013)

i5 4570 ,NVIDIA 750M , 8 GB Ram




Update (20.11.2018)

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u7600 does not give 3.3 and 5v.


pin 16 = 11,8v

pin 18 = 2.3V.

pin 12 and 24 = no voltage ..

should I just try to swap the ic or is it a broken elko?

Update (22.11.2018)

There was a short to PP3v3 S5 line. because of defective C9480, C9615 and R9612. The distance is closed. I think the ISL62383C did not survive ed:(

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Update (04.12.2018)

u7600 is new :)

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Unfortunately, U7900 does not output 3.3v. now he has to be swapped :/

Answer this question I have this problem too

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It does look like you did get a some water inside as there is green & white corrosion. This is going to take some effort to fix between the SMT caps & resistors you will likely need to swap out a few chips as well.


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Time for a new power supply iMac Intel 21.5" EMC 2638 Power Supply Replacement and here’s the needed part iMac Intel 21.5" (Late 2012-2019) Power Supply and [linked product missing or disabled: IF173-005]

A system with no diagnostic LED’s tells me the systems power supply is shot. It’s also possible the logic board is damaged as well here.

The newer iMac’s (2012 onward) are more sensitive to power issues. Make sure the buildings wiring is in good shape: Outlet is properly wired & grounded, the main power feed entering the building is properly grounded and the breaker is not overloaded.

You should have a good surge suppressor and if you are in an area with power fluctuation or lightening I would get a good UPS. Also, make sure any device that is connected to the iMac is also protected! I’ve seen lightning enter via either the USB or Thunderbolt ports as well as the Ethernet network.

Update (11/20/2018)

It looks like you had a visiting spider!

I see a whitish material around the chip. Its possible just cleaning it off throughly will fix things. Use some 85% isopropyl alcohol and a toothbrush to clean it up and then use a blast of can’ed air to blow the material away.

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iMac Intel 21.5" (Late 2012-2019) Power Supply Image


iMac Intel 21.5" (Late 2012-2019) Power Supply


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hello Dan, the power supply delivers clean 12V. I will tomorrow 3.3 v and 5v supply check at the LB on the U7600 IC


it was not a spider;)

It was flux, I cleaned with IPA. the picture was just old ^ ^


Is ISL62383CHRTZ and ISL62383HRTZ are the same?

could not find a difference


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@kamha let us know what board your computer has so we can follow you along during your diagnsotics. Also here is what apple says reasons for LED 1 being off could be. Check on your AC side first before going to deep into any logic board issues.


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.

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.

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hello, I have the logicboard input (J600) and PSU output voltage 11.7 V.

at J601 pin 1 are 3.4 V, with power on press 0.0V.

Tomorrow I will get a new PSU, and will test it :)


new power supply brought no success.12V are there. I'm always missing 5 & 3.3 V on u7600


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Question, what was the problem. i changed the psu and still no led lights are turning on.

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Sounds like your logic board Bucks and/or VRM's got zapped by a surge (lightning)


so if it doesn't show any led lights on and i already changed the psu it will definatelly be a board issue. i might have to change the board then. Thank you so much BTW.


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Hi, I have a similar problem with 3 different boards:

  • 2 ea 820-00292 Imac 5K 2015 boards
  • 1 Imac 21.5” 3.0Ghz GPU-555 2017 board

All 3 have no LED at all.

Checked voltage from PSU and it’s 12V OK

Tried 3 different PSU’s and all the same, and the PSU’s work with a normal board. SO ruled out PSU.

Checked voltage on first LED and 0.5V.

So some short in the trickle power circuit?

Any suggestions appreciated.

Am a newby on board level repairs but am interested to learn.



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Hey, I have the same issue, but I also replaced the motherboard and the problem remains!!!! no idea whats the issue


Did you check the AC power cord and it’s connection internally as well as replace the power supply? That’s always the first things I do on a system with not diagnostic LEDs.


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willi will be eternally grateful.
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