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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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EMC 2742 late2013 , iMac 21.5 LCD ON, LED-backlight dark flickering


I have a 21.5'' Late 2013 iMac Model A1418 (EMC 2742) , that was sold in JAPAN.

Display’s backlight doesn’t work now, When you look carefully, the thin liquid crystal display is shown.

Now, I’m testing: Thunderbolt2(edited from 3) to HDMI external display

So, How to check for broken parts?

What is the probable cause of this type of failure?

Where on the logic board is the fuse element for the backlight?

My son's MBP has the same symptoms and repaired the logic board, by Apple U$D450.

Are there any method for below,

What should be input to the terminal of the display power connector to light the backlight? for always LED backlight-ON use I will... If I can do.


Update (03/01/2019)

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Thank you Dan,

This is the screenshot of connected external display (TB2 to HDMI adapter to ext. Dell Display)

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This is screenshot re-conect ORG back-light darkdown display de-touch Ext.display DELL. It looks LCD Montor sensor is Allive.


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Shutdown Reason,Fan Diagnostics,Sensor Diagnostics,Battery Health

Normal,The fan appears to be working properly.,Temperature sensors appear to be working properly.,This Mac does not have an internal battery.


I tried to video-record "stage lighting effect" , there was no again bright of display.

However, another case incident was happen "flickering falsh and very dark" , Please see Uploaded Video.

When flickering, the brightness is differnt than Backlight-”off”, It was ON very small darkness.

This is more and More dark than normaly minimunum dispray brightness adjust (I feel about 1% as normaly brightness).

In the video, I am pushing the button, but I feel it is timing unrelated to flicker.

The video was recorded brighter than I saw with my eyes.

Flickering does not last forever.

Flickering did not happen after this recording, display kept very dark.

When "stage lighting effect" at once time ago , display LED worked normaly brightness about 50%.

The currentry flickering & brightness of LED-bucklight.

Where does this symptom occur when something is wrong?

Respondido! View the answer Também tenho esse problema

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Does the external display work?

Did you take the display assembly off at some point?



Now, External display is working well but slow response.

ThnderBolt-HDMI to external display SONY

After LED back-light lost, I took off Orginal display as Two connectors from logic-board for find SONY display.

few times restart iMac , then clean installed old OSX, then

Now working on Mojave.

Few times switch display .ORG 21.5 & SONY and both display , or AppleTV.


アプリをインストールするTG Proメインウィンドウのスナップショットを撮ってここに貼り付けると、Adding images to an existing question が表示されます。

Install the app TG Pro take a snapshot of the main window and paste it here for us to see Adding images to an existing question


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Solução escolhida

診断を受けるにはフルバージョンを入手する必要があります。あるいは、システムを再起動してキーボードのDキーを押して診断に入ることで、Appleオンボード診断を実行することもできます。 残念ながら、Appleの診断はTG Proほど有益ではありません。

ディスプレイを取り外したときにディスプレイのサーマルセンサーが損傷したか、ロジックボードへのケーブル接続が損傷したかのどちらかと思います。 どのセンサーが応答していないかを特定できるまで、どこを見ればいいのかわかりません。


You’ll need to get the full version to get the diagnostics or you can also try running the Apple onboard diagnostics by restarting your system and pressing the D key on your keyboard to enter into diagnostics. Sadly, the Apple diagnostics is not as informative as the TG Pro.

I’m suspecting your either damaged the displays thermal sensor when you took the display off or you damaged the cable connection to the logic board. Until we can localize what sensor is not responding I can’t tell you where to look

Reference Mac startup key combinations

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Does diaagnostic of TG Pro Full Ver. find damege points?

I tried ORG display check.

It looks OK of the displays thermal sensor.


TG Proのフルバージョンから何がわかりましたか?

What did the full version of TG Pro tell you?


i found almost properly. Do I have to check more diaagnosticmethod on TG pro?

Date,Time,CPU Core 1 (C),CPU Core 2 (C),CPU Core 3 (C),CPU Core 4 (C),CPU PECI (C),CPU Proximity (C),GPU Diode (C),GPU Diode (Analog) (C),GPU PECI (C),GPU Proximity (C),LCD Monitor Proximity (C),LCD Monitor Proximity (C),PECI System Agent (C),Platform Controller Hub Die (C),Memory Module Proximity (C),DC In Proximity (C),Power Supply Secondary Heatsink (C),CPU Average (C),Computer Average (C),Main (RPM),Fan Average (RPM),Shutdown Reason,Fan Diagnostics,Sensor Diagnostics,Battery Health

2019-03-03,22:27:53,34,34,34,31,34,29,31,N/A,34,27,23,24,28,33,26,26,26,33,30,1400,1400,Normal,The fan appears to be working properly.,Temperature sensors appear to be working properly.,This Mac does not have an internal battery.


TG Proの診断機能から何がわかりましたか?

Again, what did the diagnostics within TG Pro tell you?


Diago. tell

Last Shutdown : Normal

Fans : The fan appers to be working properly.

Tempratures Sesors : Temprature sensors appear to be working properly.

Battery Health : This Mac does not have an internsl battry.

All green. Battery is grey


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