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Model A1419 / Ende 2013 / 3,2 und 3,4 GHz Core i5 oder 3,5 GHz Core i7 Prozessor, ID iMac14,2

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Please Help me, Screen Problem after Replacing HDD with SSD


I did it twice before, replacing faulty hard disks in two iMacs, everything went ok, this 3rd machine (only one normal 3TB HDD), i just swapped the HDD with SSD (Samsung 860 EVO) following the guide, with the frame and heat sensor, upon testing I can hear the startup sound but the screen showing just strips, from the rubbish I can sense the system is booting from internet or just flashing folder, the usual sign that no operating system, I double checked the cables and can’t find anything wrong as far as I can tell, but I admit the data cable (the wide cable with lock) may be pushed hard when trying to insert it back, did I damage the screen or the board?, please advise…

I tried to remove and reinsert the cables but nothing changed, it is as it is…

Here is a preview:

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Please accept my question and help me, I have no clue without your answer…

Update (04/27/2019)

Hello guys and thanks for your responding, but it seems that there are some conflicts between my updates and your answers, so here is what I did…

after I swapped the HDD and fall into the screen problem, I swapped back the original HDD that has mac os on it and boot the iMac, the same screen issue continue but this time after the initial boot, the screen went black completely with no back light at all… so I connect the iMac to external Display (my Samsung 50” TV) and I can see the output but it is continuously flashing on & off, the keyboard, the mouse and the system is responding but the flash never stops…

I tried to search in the internet and I notice that many places point to the cable as a suspect so I connect another iMac using the same cable and the output was fine without any flashing…

so the iMac display has the problem shown above and the output to the external monitor is flashing continuously…

the iMac is working, programs and responding but the display is showing as above during the boot after that it turns off when the mac os reaches the log on screen, on the second monitor I see everything but with continuous flashing…

I double checked the display cables and the sockets on the board and they are fine with no visible marks as far as much as magnified as I can tell…

where does this put me…

I appreciate any information to lead me, should I give up or there is something I can replace for sure…

thank you all

Update (09/18/2019)

Dear @danj , @docmofix

here is something new and I didn’t expect it by any means…

today I received another 27” iMac, Late 2012 (EMC 2546) (with a dead hard disk) which is compatible with mine Late 2013 (EMC2639) and I connected the display from that machine to mine (which is suppose to have a problem in display), to my surprise the screen also shows the same symptoms as mine… I also connect my screen (which is suppose to be faulty) to the other iMac and it works perfectly…

So it is not the screen at all, my screen worked perfectly on the other iMac, also an external HDMI monitor connected to my iMac works perfectly which means ??

where does that puts me? what part of my iMac does not work?

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You swapped HDD with SSD? Have you downloaded mac os ( or any operating system, that you like ).


No, I was just testing the imac, I just switch it on booting in recovery from internet and the screen was not working from the first start up...



I put back the original HDD that has operating system on it, when starting the screen is the same but after the initial boot, the screen turns off completely, no back light no anything, when connecting to external monitor using mini port connected to samsung tv 50” using HDMI, I can see the output but strangely the output flash on and off continuously, the keyboard, the mouse is working, I can logon but everything is flashing on and off...

Where does this put me?

Thank you


I think, that display might be kind of damaged, because, you had to take the display off. When you opened, the display or placed it back, you could had damaged connections? You should check the connections.


I appreciate any information to lead me, should I give up or there is something I can replace for sure…


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Sadly your display got damaged. During the the process of taking it off you likely damaged it. its very easy to damage if you don’t use the correct tools and follow the technique as outlined in the guide iMac Intel 27" EMC 2639 Display austauschen and here’s the needed part [verlinktes Produkt fehlt oder ist deaktiviert: IF174-035]. Presently iFixit is out of stock here’s the Apple P/N 661-7169.

Update (04/28/2019)

Onboard LED diagnostics

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Here's a breakdown of the onboard diagnostic LED's:

* LED 1 - Indicates that the trickle voltage from the power supply is detected by the main logic board. This LED will remain ON while the iMac is connected to the AC power. The LED will remain on even when the computer has been shut down or put to sleep. The LED will turn off only if the AC power is disconnected or the power supply is faulty.

* LED 2 - Indicates that the main logic board has detected proper power from the power supply when the computer is turned on. This LED will be ON when the computer is turned on and the power supply is working correctly.

* LED 3 - Indicates that the computer and the 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, then the video card might be installed incorrectly or need replacement.

* LED 4 - Indicates that the computer and the LCD display panel are communicating. This LED will be ON when the computer is turned on and video signal is being generated. If the LED is ON and there is no image on the LCD display panel, the LCD display panel or inverter might be installed incorrectly or need replacement.

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Ok, it could happen, I will accept that, it happened once with me years before on a 21inch iMac and I did follow the procedure with the right tools twice before with no problems at all but it still can happen, but what about the fact that the output to external monitor is also flashing continuously ON & OFF? Is that because of the damaged display, should I try to run the iMac without the display and connected to external monitor? The idea is that I don’t want to end up buying another display and it is not the issue here, can some one tell me a way to make sure… it is my mistake and I will buy to fix it if it is the faulty one….

thank you all really for your attention…


OK, let's walk this back ...

Take the display off and disconnect it. Now plug in your external and restart the system are you able to get an external image?

Looking at the onboard diagnostic LED's what are they telling you? Look at the info in my Answer above.

Before you took the drive out did you make sure you don't have a Fusion Drive config in this system? Basically, you could have a second drive still installed (Blade SSD) which is confusing the system.


Thank you Dan, I will update you soon about the result of walking this, I just caught in the middle of some work, as soon as I have time I will perform the steps...

Just to let you know, this machine has no fusion, only one 3TB HDD, I manage to put it back and when I started the iMac, the system did boot normally with the screen still showing rubbish and the minute the system reaches logon, the display turn off with no backlight at all, but on the external monitor I can see everything but it kept flashing on & off, I test the cable on another machine and it is working fine but the idea of disconnect the monitor and start the system did not cross my mind, so I will observe the diagnostic d on both situations, with and without the display and update you...


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I have found some things, that might help, you should try those:

  1. Disconnect all peripherals
  2. Restart in Safe Mode
  3. Run Disk Utility
  4. Reset NVRAM (or PRAM)
  5. Power up your Mac with the Startup Manager and select your Startup Disk Manually
  6. Launch Single User or Verbose Mode with Terminal
  7. Reinstall macOS or OS X
  8. Run Apple Diagnostics or Apple Hardware Test

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Hi @atheerioy, I’m having the same issue but still don’t understand the root cause. Have you been able to figure out what was happening and hence fix it?

Have you been able to fix it? I have exactly the same issue.

Also the 4 LED’s are ON

Many thanks in advance for your help.

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Hi @docmofix , sorry for my late answer, busy…, unfortunately, I was unable to resolve it despite all I did…

The 4 LED’s are ON when exactly? here is my test:

I reinstalled the original hard disk that still has the OS that was running Ok before I opened my iMac and I connect the screen back and start the machine, when I heard the startup sound, the 4 LED’s were ON but the screen still showing rubbish (which is the apple logo and the load progress bar), after that when the system reaches the logon screen, the 4th LED turns off and the screen too, completely off, no backlight no anything at all but on my external monitor connected through HDMI everything was OK, I logged on, browsed internet, start even adobe photoshop…., all was working…

I switched off the machine, disconnect the screen but kept the external HDMI monitor and start the machine again and had only 3 LED’s are on, so far the machine was normal accept the fans were running in full speed and that is normal if you notice the heat sensor connected on the screen…

I switched off again and I remembered some files I need so I start the machine in disk mode, for 20 minutes I can see the dancing logo on the external monitor and the high fan running while I copied everything…

something went wrong when I opened the machine the first time, I took care as I did on my two previous attempts but this time something went wrong…

All I can say but I am not sure, I remember I pulled the screen a little bit hard to free it from the machine, just a little bit because it was still stick, that is the only thing I didn’t do before…

I am not sure but very soon I will have three machines with dead hard disk to replace, I will try to test the screens and see, I will post here of course…

for everyone replied to me and offer me any suggestions, thank you all


@atheerioy - There is a thermal sensor within the display as you took the display off the sensor was lost to SMC which is why the fan is running high and you'll notice the system will be sluggish as well.

Once the display is reconnected the forth LED will come back on and the system should be back to normal.


@danj , that is right, but in my first test, the display was connected, the fan working Ok and ALL LED's were on at startup but the display was showing rubbish but as soon as the system reaches logon screen, the display completely turns off and the forth LED turns off...


Ouch! That does sound like your display is having problems. If an external works, if the external fails then your logic boards GPU is having issues.


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I have the same problem on a late 2012 27” iMac after a SSD install. On this one, after the screen is blurry like that, it switches resolutions down to 720p. Then that is the only resolution it will display. The problem is a faulty display connection. It could either be the display data cable or the socket the cable plugs into. The socket itself is easy to break tiny (not easily observable with naked eye) pieces off and get them stuck between pins, meaning the cable will not fully seat or will not make a connection on all pins. I could only see it with camera zoom on my phone.

Broke off a corner

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Piece of metal in connector

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Anyway, try replacing the $20 display data cable. Or try getting a magnifier to look at the connector on the board. It wouldn't seat at all until I got the piece out. Now it does the behavior I described at the beginning, including the blurry screen. It seems to realize that the display is going wrong though and drops to 720p. So subsequent boots are no longer blurry like that but really pixellated from too low of resolution. I have to reset nvram to get it to try the higher resolution again. I’m afraid I will have to replace the board where the socket is.

This appears to have been a really common problem even fresh from the Apple Store. As evidenced by this compilation of questions about the same thing. The owner of this iMac tried to get the failing hard drive replaced at the Apple Store (after warranty), but they refused to do anything requiring the screen to come off. I should have taken this as a hint not to do this repair. They probably already knew from warranty work that these are very fragile to work on.

Update: I tried replacing the display cable but same effect.

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Has anyone found the solution for this? I do not believe the issue is with the screen/ connectors or anything related. I have replaced 10+ SSDs on these machines with no problems.

When I boot off the original HDD there is no fault. However when I boot off the new SSD the screen becomes pixelated. I will try another SSD and see if that solves the issue.

If anyone has found a solution please let me know!

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I hope that it is the SSD in your case. However, I've never seen a drive cause display problems. It either doesn't show up, errors on boot, or is slow/errors in the OS. Your update on 09/18/2019 indicates the problem is on the logic board because your screen works properly when connected to the other iMac's logic board.


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it is not related to the ssd, I put back the original HD, I started without HD and no difference at all, eventually I found another another similar logic board from a faulty machine and the HD and ssd worked with…

the only two reasons I can come up with are:

  • I some how damaged the board accidentally, a scratch here or there…
  • a matter of static electricity…

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Thanks for getting back to me. I installed a fresh OS and that did improve the situation slightly. I then upgraded the parallels software that was running on the mac and that seems to have sorted it for now… I also noticed after a PRAM reset on the first time loading it worked okay but if I reset again then it would show the pixelated screen. Very strange. I think it must be due to cloning of the original HDD.


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Atheer wird auf ewig dankbar sein.

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