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sometimes (not always) a strip of the whole bottom of the screen flickers
Edit with the video:
Thank you for your comment and I apologize for my English if it is not correct.
I just uploaded a video on youtube with the problem that my imac has. It does not always, it does so randomly.
This is the video of the problem
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Sadly, it sounds like the displays TCon board is failing. It converts the signal from the logic board to the LCD display. This is part of the display assembly and not really replaceable. Here's the IFIXIT guide: iMac Intel 27" EMC 2546 Display Replacement. Make sure you get the Adhesive Strips kit with the needed tool to open the system. As for the display you'll need to take yours out and locate the manufactures number to get the correct one (Apple had two versions).
To verify plug in an external monitor this should not show up on it.
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@danj are you okay? This answer is not up to your usual standard. T-con board for "strip of the whole bottom of the screen flickers" is way, way off. T-con boards are never responsible for anything going across a screen. I give you that it is possible that this panel needs to be exchanged but that has nothing to do with T-con boards.
@oldturkey03 - I would have agreed with you if i hadn't seen it with my own eyes! We had one the other day and we found it was a cold solder joint on the TCon. Pressing on it just so fixed it.
in years past you would have thought the LVDS was bad or the backlight. With iDP connections things are different! Here's a YouTube vid you can see the effect: iMac Late 2012 Screen flickering This is not a backlight failure.
Ahhhhh, no! Still not a T-con issue. Post the model of your panel and some images (I know you know how to do that:-) of where that cold solder joint was.
Sorry @oldturkey03 it was shipped it out for exchange. It was in the London office which encountered it. I was on a video link with him when I saw it.
At first I was thinking the ribbon cable connection or the connector. We tried a second screen with no problem and a fresh cable. The external monitor did not show the symptom either.
What are you thinking??
Looking at the datasheet for the panels used in that model iMac and by the brief description we have (it will definitely help if and when we see it, my money is on bad gate drivers if it is not the backlight. Again, this can be verified when we see what we are dealing with. Anything vertical I would maybe agree, but horizontal presentation (even like the one in the video) goes against the T-con
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gonval "a strip of the whole bottom of the screen flickers" is most likely caused by a bad backlight. It is possible to replace the backlight strips. There is also the possibility of failing backlight return filters. It will help to see what you see. If you can post some images of the flickering across the whole bottom we can most likely verify this. Use this guide Adding images to an existing question for that.
gonval2002 if you can and if you have your iMac already apart, give us the exact model number which is written on the label on the back of your panel. It is possible that your panel has issues with the Gate drivers but most likely not a T-con issue.
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@oldturkey03 - Time to put on your thinking cap ;-}
You talked about the gate drivers which chip would that be. if you look at the backside of the display under the metal plate it that the chip to the left? (I'm doing this from memory) Thats the one we pressed on.
@danj depends on the panel.
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Did you bang or drop the system?
by Dan
No, the system never was bang or drop
by gonval2002
gonval2002 nothing wrong with your English! thank you for adding the youtube video. This does loot like a gate driver issue. You would have to take your iMac apart to see what model LCD panel this is. Otherwise we could try to find a couple similar panels and find those drivers for you. Ultimately you may still have to change the display panel, if we cannot locate the right circuitry. Let's see what we can find out.
by oldturkey03
Thank you very much for your help.
I don't have take mi iMac apart.
The truth is that I am a little disappointed by Apple, because it does not speak very well of Apple that in 4 years I must change the screen twice and the motherboard on one occasion.
Thanks again :)
by gonval2002