Persistent horizontal lines appear on iMac screen

This is clearly a hardware failure and the only solution is to replace the screen. No one on this forum can fix it for you. I doubt it is something most users have the tools and training to do themselves. It is an expensive repair, but I do not see any other options.

About 40 others seem to have posted with a similar failure. I do not know how common it is; there are many millions of iMacs M1 in use. Where I work, we have thousands of this Mac model in daily use and I have not heard of any failures like this. I do not doubt that your failure is real, but it might not be very common. All electronics have some non-zero failure rate, I believe these parts are mass produced overseas, a small fraction of all electronics like this have defects. I think the way to protect against this type of repair bill is to get Apple Care, but that is hundreds of dollars spread over several years, I buy it anyway for my personal Macs (which include one iMac M1). If I look at all the iPhones and personal Macs I have owned and how often I used AppleCare for a "free" repair, I have paid way more for Apple Care than I would have for the repairs myself. But I still get Apple Care for peace of mind as laptops and iMacs and iPhones continue to increase in cost ...

@cristobal2

Has it returned? Have you increased the brightness to 60% or more? Perhaps it's triggered when things heat up inside and the board experience thermal expansion and contraction causing the CPU/GPU SOC to fail because of heating up, cooling down reaction?

To make the best of a bad situation you could always use a separate monitor with the iMac. It's an annoyance given that there's already a display taking up desk space but at least you wouldn't have to get another computer. I kept several older iMacs going that way. Just make sure that if the display is really starting to go that you set this up before it is fully gone. You set up the second display as mirroring the first one and with iMacs this has to be done while you can still navigate the main display.

I bought mine in June 2021 and since it was a new product on the market I decided to pay 150€ to extend the warranty (store's insurance program) to 5 years. This issue happened this month and the store replaced the display with no additional charges.

They didn't specified the problem but it's not software related.

Two ports, Part number ends in PO.

Sadly, this is not a software issue. You can easily see that if you make a backup. Wipe your drive and reinstall the OS NEW. As many have tried, it won't go away. Component has failed and will need hardware repair.

It´s a hardware issue.

But, because the (1 dollar) component it's causing it is not accessible, the only fix is an all-new (600-800 dollar) LCD.

My advice, at this moment, is to get a second monitor and turn the brightness of the iMac monitor to ZERO to protect it and delay its definitive failure as long as possible.

A 4K (27”-28”) monitor, with 350nits (or cd/m2) minimum, should work fine.

Color calibration will be the biggest problem if you buy a cheap monitor, but I was taught a trick which is to use the iPhone (or iMac monitor) to do it easily, by matching the monitor to the phone (or iMac) display. There are several videos to help with this technique.

I have discovered that if you keep the display at half, the black lines remain at a barely there level and the screen remains cool to the touch. I think it is using the display at full that causes the problem. It is burning too bright and the machine is not equipped to handle it and then the screen burns itself out.

MacBooks with FlexGate have similar problems. In the MacBook, this is caused by the LVDS cable, which is fixed to the PCB of the lcd assembly and not easily replaceable.

However, the LVDS cable in the iMac can be replaced. Has anyone had experience with this or replaced this cable before?https://www.ebay.nl/itm/255809013613?mkcid=16&mkevt=1&mkrid=1346-175129-2357-0&ssspo=9_Kc3GPRQIS&sssrc=4429486&ssuid=2ViFqcZVSqK&var=&widget_ver=artemis&media=COPY).

From what I've been told, the problem isn't with this cable (which connects between the iMac main PCB and the LCD PCB and would be easily replaced) but with the cable that connects the LCD PCB to the LCD itself.

And to access this cable you have to peel back the LCD glass, which is difficult and easy to damage or break.

That's why Apple's solution is to replace the entire LCD...

@allrighty

Read My other comment on the first page, I posted a case number, the moderators removed the full number but I think that should be enough to prove your case. I believe any apple supervisor who reads this thread, in their right judgment would agree that the issue is APPLE manufacturing and this is why they were willing to offer it to me to fix it.

So if we all calmly and kindly let them know and get to the top level and make a request, they will make the best choice to protect their own brand for long-term success.

I too have the same issue, Apple should recognize this defect and sort out this issue free of cost for all those affected. I am very unhappy with this situation, the screen replacement cost is pretty high. :(

Thanks for letting us know your situation, I too contacted Apple support but they denied free replacement so I paid the full cost for the screen replacement 15 days ago, can someone advise if I can request a refund? I will try to raise a refund request through chat support soon...

Just want to add I too have the same problem.

Not sure if someone has written about it here but, several days before it started to happen, I heard something unusual—the fan started running, even though I was not doing anything labour intensive.

Since this has become apparent, should I just go bring it to the local service provider right away or should I contact Apple first?

This problem is limited to the M1 24" iMacs. However if you decide to go the replacement route you might consider what I did: got an Mac Mini M4 with a external monitor.

I go the M4 with 16 GB of RAM and a 1 TB drive for $999. The monitor I got is a 32" LG 4K monitor with speakers for $331. If you can live either the minimal Mac Mini speaker you can take about $100 off the price or go with a 27" monitor. A similarly configured 24" iMa is $1900 or about $500 more than the mini.

Just some food for thought.

From what I’ve seen here in the Apple Community, continuing to use the iMac despite these issues may not just result in a gradual worsening of the lines, but it could potentially lead to more significant problems. For example, there are reports in this very thread of a user experiencing a complete screen blackout, and another who mentioned a burn mark appearing on the edge of their monitor. While it might seem manageable now, it’s worth considering that these defects could escalate, potentially leading to more severe consequences. If possible, it might be a good idea to address the issue proactively.