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Hi, 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. Thanks Update (03/01/2019)

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

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

diagnostic 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?

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。 参照Macスタートアップキーの組み合わせ 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