Model A1419 / Late 2013 / 3.2 & 3.4 GHz Core i5 or 3.5 GHz Core i7 Processor, ID iMac14,2

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LCD Backlight problem I mac27 late 2013

Hi All,

I have received the above imac for FREE : ) with the below issues and trying to figure out if it is worth to fix it. I hope you'll be able to help me out :)

Internal Dispaly is not working - external OK

Diagnostic LED's - 1,2,3 OK - 4 is off

Replaced LCD cable ( 2 pins were bent and sticked to each other )

I did a SMC/PVRAM Reset

A faint image is not visible ( checked in dark room and flashed the light on )

Run hardware test : may be an issue with System Management Controller PFM006 and with the display VFD001

The visual check showns blown part - as on the attached link( not shure if it has been caused by connecting a faulty cable and have not found logic board schematic to figure out what is it - fuse / capacitor etc....

Is there any way to test LCD panel it self ?

Block Image

https://s33.postimg.cc/vk0hkmpvj/de29ee7...

Cheers

Pete

Update (06/05/2018)

The L4400 has now been replaced and the 4th LED is on !!! There is only a lot of stripes on my LCD unfortunetelly ....

Block Image

What do you think guys ? is it dead display or something else ? - when I touch the LCD connector on the logic board the stripes are changing.......

Beantwoord! View the answer Dit probleem heb ik ook

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From the picture it looks like there is a cap blown right near the Lvds connector. Yea, there’s defintely something blown on your logicboard.

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What does diagnostics tell you now?

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HER Zygiel (Herzygiel) post some good pictures of your connector. Have you connected an external monitor to see what that shows you. It could be a panel issue but it could be an issue with the board. There is probably a reason why the part shorted out to begin with.....

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The diagnostic has changed from PFM006/VFD001 to VFD004/VFD007. The external monitor is still OK - I will take the picture of the connector this aft.

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'''HER Zygiel (Herzygiel)'''  This just for an FYI. As you already know, your computer and your LCD are not communicating. Hence the LED 4 off. No, you cannot test the LCD without having special equipment at least an LED backlight tester would be required. If you have the equipment you of course could, but it is unlikely since you are asking.

Diagnostic LEDs (A)

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.

The part that shorted out for whatever reason is reference designator L4400 which is a 120 Ohm 3A fixed inductor (ferrite Bead) in a 0603 package. A Murata BLM18KG121TN1D would be a perfect fit. They are available at Mouser.com Digikey.com Farnell.com and of course ;-) on ebay https://www.ebay.com/itm/Fair-Rite-0805-...

Block Image

Without the component you are not getting the 12V to the LCD. No power to the LCD - no 4th LED!

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Thanks guys!! There is 12V at one side of L4400 and 5V. I have just ordered this part and planning to replace it mid of next week. I will let you know ASAP.

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HER Zygiel (Herzygiel) zal eeuwig dankbaar zijn.
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