Persistent horizontal lines appear on iMac screen

Hello everyone,

I’m adding my voice to the growing number of iMac M1 owners experiencing persistent horizontal lines across the display.

• My iMac is the 24-inch M1 (2021).
• The lines appeared suddenly and are worsening over time.
• When I connect to an external monitor, the issue does not appear, which suggests it’s a built-in display hardware fault and not a GPU/software issue.
• The lines do not appear when taking a screenshot, which suggest according to the apple advisor on the chat that it is a hardware and not a software issue
• I’ve seen many others here and on Reddit/MacRumors describing the exact same problem, often 1.5–2 years after purchase.

This seems to be a widespread defect, not accidental damage. It would be great if Apple could officially acknowledge this and provide support—whether through a repair program or extended coverage.

Has anyone here successfully escalated this with Apple Support and received a repair (in or out of warranty)? If so, could you share how you approached it?

Thanks for any advice, and I hope Apple is listening to the many of us dealing with the same display failure.

Hi Kerdkiat,

The issue lies in an internal LCD cable itself, which overheats and ends up short-circuiting. To mitigate the problem for now, reduce the screen brightness and use an external monitor as a temporary solution. There are affordable 4K options available with brightness levels of 350 nits or more — anything below that will be noticeably inferior to the iMac’s panel. If colour accuracy matters, choose a model that supports proper calibration.

This approach gives you time to contact Apple and present your case calmly. Always remain polite, yet persistent. Explain the situation clearly and continue to insist, courteously, until you receive a concrete answer. This is a design and manufacturing issue, and in some (rare) cases Apple agrees to replace the display. However, it is well known that the problem is likely to reappear in the future, since the fault comes from the LCD module itself.

You can also purchase a new panel and replace it yourself, but the long-term outcome tends to be the same, precisely because the underlying issue remains unchanged.

If Apple does not accept responsibility, it may be wise to reconsider buying fully integrated devices. If what we truly value is the operating system, then that is what we should continue to buy — just the computer part. Mac mini is a much more inexpensive and versatile alternative.

At my company, once we became aware of this issue and of Apple’s refusal to take responsibility, we decided to sell all our iMacs and switch entirely to Mac minis. It proved to be a more reliable and sustainable approach, avoiding the recurring risks associated with integrated displays.

Displays — often of even higher quality — can be found outside the Apple universe, whether you want top-tier performance or a more budget-friendly option.

Good luck with the process.

I'm doing exactly this now. Using a second monitor, and using the Lunar app to turn off the defective main display. Apart from the display, everything else is working as it should.

Not a software issue. My workaround is using an external monitor, which works fine. Also I can share the screen to my smart TV, which also looks fine.

No, this is a hardware issue with the iMac itself.

I bought an imac m1 2021 and black lines started appearing then eventually this weird blotch of purple color started showing on the top left hand screen. Then it gradually got worst to the whole screen is black and the computer is unusable. I also noticed a burn mark up in tge left side of the screen where the putple blotches of color was. I just read someones post that took his computer with same problems to a repair guy to get a diagnosis of it and said something like there is a faulty cable that overheats so this explains it. Im really angry as Apple told me that can’t do anything because it’s out of warranty. I’ve been using Apple for decades and I always take care of my equipment. I use it for work feel really cheated because this computer was defected from the beginning. There was so many issues.

Jotap62 wrote:

Dear Old Toad,

According to Apple support, it's an LCD malfunction and the only solution is to replace it.

So it's not a software problem.

It's a hardware problem.

That's already established.

Then maybe the most economical path forward might be an external 3rd party monitor. When you upgrade to a new Mac it can be a second monitor for that Mac.

Some claim "  Tim Cook's official Apple email (tcook@apple.com). Cook almost never responds directly but Apple, like most large corporations, has an executive response team that monitors his email inbox and manages and escalates customer complaints. Include the information you've found about this being a widely reported defect. Mention your long history as an Apple customer and how this experience has shaken your faith in product quality. A member of the executive response team will most likely respond, and they could well wind up authorizing the repair at no charge.

PS: For me even repair at no Charge don't feel fix this Line problem partly is All due to " Design flaws how and why they do back the same again " This line issue first surface from M1 iMac , now even M3 iMac which I using it also has this problem...

There might be a connection between auto-adjustment of brightness and the onset of flickering. My iMac first had the flickering one week ago. I turned it off and on. The flickering disappeared, but a black line persists. Since then, the flickering appeared a few times more. It seemed start when there's a change in environment light. For instance, I pulled down the curtain. My room became darker. The brightness of the display changed (I had auto-adjustment of brightness on). Also appeared flickering. I then disabled auto-adjustment of brightness. Flickering hasn't re-appeared since. Just to share my observation, in case it might be useful.

My advice is to turn off the LCD lighting on your iMac (set it to 1).

By reducing the brightness you'll be able to see that the temperature at the top of the LCD becomes normal and the worry about over-temperature will disappear.

Then buy a new external monitor.

There are very good monitors available relatively cheaply.

I worked like this for almost a year when my iMac was broken and without any problems.

It's the same as having a (very expensive) Mac mini...

But at least you can keep working until Apple sort it out.

I purchased four 2021 M1 24" iMacs for my office in Taiwan, across different months in late 2021. All of them have been well cared for, yet each began developing the same screen issue one after another starting in March this year. At this point, 100% of my units are affected.

From reading various threads and forums, it appears Apple has occasionally offered one-off free repairs to users who know how to push for them. For example, a petition requesting a Service Program quickly led to Apple granting free repair to the petition's initiator.

The iMac line is positioned as a premium product in the personal computer market. My previous iMac lasted over seven years without issue, and many older Intel-based models still run flawlessly today. Selling a product with such widespread defects undermines that reputation. Until Apple properly addresses this issue, I will be cautious about purchasing new Apple products.

I from SG, same replay from other SG iMac users.

what I have research

​Even tech repair iMac do mention this 

" Known iMac 24″ (M1 2021) Screen Line Defect: Recently, a flood of user reports has surfaced about horizontal lines permanently appearing on the 24-inch M1 iMac’s display after ~2 years of use. Apple hasn’t officially recalled this, but evidence suggests a hardware design flaw. Technicians discovered that a flex cable in the display carries high voltage (around 50V at full brightness) and tends to overheat and burn out over time, causing short-circuits that produce black horizontal lines. Unfortunately, the only reliable fix for this issue is to replace the entire display assembly, because the cable is bonded to the screen. Apple Support has generally told affected users that an LCD replacement is the solution. However, replacing the screen is costly (often on the order of US $600–$700 for the 24″ iMac), and if the underlying design hasn’t changed, the problem could recur in a couple of years. "

PS: I NEVER use Full brightness. I always set Auto brightness. According from the tech , EVEN you get fix the problem Could Recur in a couple years....

Check out my replay. Tech do mention " Design flaws " on M series iMac. I Never know M series got what Lines suddenly appear issues after using one year or so. Just Happen this weekend I use my M3 iMac as usual. Wake up the iMac and suddenly notice there are lines appear on the bottom of my iMac.

I do owned other old iMac , all at least the screen is Ok one is bought in 2015. The screen will turn to pinkish hub and will have burn mark easily but that is OK , after a while it will gone and since already use More than Two years till now. But Cannot accept is this M series iMac , next I own M3 iMac only bought in 2024 and haven't reach two years Suddenly lines appear.... Now I worry is the lines will spread to the entire screen literally you can't view. Even the lines now appear on the bottom of my iMac screen I already feel..... A lot already bring their iMac go Apple store bring up this case of M series flaws but Same old reply , Have to pay get it Fix.

Only some like managed to get fix Free but thought lots of hassle feedback here and there. Next Even it get fix, the Problem will come out. Which the tech mention.

Here is what It mention " " Known iMac 24″ (M1 2021) Screen Line Defect: Recently, a flood of user reports has surfaced about horizontal lines permanently appearing on the 24-inch M1 iMac’s display after ~2 years of use. Apple hasn’t officially recalled this, but evidence suggests a hardware design flaw. Technicians discovered that a flex cable in the display carries high voltage (around 50V at full brightness) and tends to overheat and burn out over time, causing short-circuits that produce black horizontal lines. Unfortunately, the only reliable fix for this issue is to replace the entire display assembly, because the cable is bonded to the screen. Apple Support has generally told affected users that an LCD replacement is the solution. However, replacing the screen is costly (often on the order of US $600–$700 for the 24″ iMac), and if the underlying design hasn’t changed, the problem could recur in a couple of years. "

My local Apple dealer was charging me $900 in order to repair the screen, I ended up buying a new display at Amazon and replacing it by myself, it cost me around $350, is not hard but you have to be careful because there are some connectors that can be break if you rip them hard... Display is now working 100% fine ( for now ) .... Thank you Apple for nothing!

What i'm thinking is that Apple is well aware of this problem, but they will not recognize it because it will cost them TONS of money, also because this is a design problem, it will affect eventually other models that share the same design, M2, M3, etc, etc.. not just M1 and this will carry a huge lost for this product, there is no other reason why they are not assuming their responsability.

Let us all report and complain this to Apple --> Feedback - iMac - Apple

I had the exact same issue as everyone here. The first few nights (2 or 3), I used multiple pixel refresher videos from YouTube (5 hours or so each time), at max brightness. Then I continue to use the computer normally but on a second screen. Keeping the iMac screen at the lowest brightness for over a week.

Also, I pray a whole bunch :)