→ Persistent horizontal lines appear on iMac screen

The day before yesterday, I got a message from my brother-in-law: Want to know something? My iMac has developed a series of horizontal lines all over the screen, more noticeable at the bottom.

And he shared a link to a discussion in the Community forum on Apple’s website. His iMac is the 24-inch M1 iMac model released in 2021. Apparently this issue is not uncommon. I’d like to quote the ‘Top-ranking reply’ in that forum thread in its entirety because it explains the issue with clarity; then I’ll add a couple of personal remarks. (Emphasis is the original poster’s.)

“Jotap62”:

According to the Apple support team I contacted, it’s an LCD malfunction and the only solution is to replace it.

What they didn’t say was why this problem is occurring after two years of using the iMac on so many computers.

So, as Apple hasn’t yet assumed that it’s their fault, what I did, given the lack of concrete answers from Apple, was to take my iMac to a technician and ask him to assess the problem to see if it’s a construction problem or just a random fault.

The explanation I was given was as follows:

In terms of circuitry, everything seems to be working properly.

The problem, apparently, lies in a cable that also powers the LCD, which is located on one of the tops of the screen, and which, in order to be replaced, requires detaching the screen glass from the LCD itself, which is a very sensitive operation and almost impossible to carry out without damaging the LCD.

So the only option is to replace the entire LCD (LCD + main boards + screen glass).

Also, according to the technician’s explanation, this cable (of the FFC/FPC type or Flat Flexible Cable / Flexible Printed Circuit) has to sustain a very high voltage (around 50V) to power the LCD (this despite the iMac’s power supply being 15.9V), and it heats up a lot!

So, what happens after a while (in this case after about 2 years) is that it starts to burn out and degrade at the connector, to the point where it lets the signals leak between the various connectors and short-circuits some of them, which ends up causing those lines that we are all unfortunately familiar with.

The level of brightness makes a fundamental contribution to this problem. Thus, the higher the brightness used, the sooner the problem occurs.

This is easily understood by measuring the difference in temperature at the top of the screen when it is at its lowest brightness level, compared to when it is at its highest. It’s quite a big difference!

When it’s at its lowest brightness, it’s practically room temperature; when it’s at its highest, you can almost “fry an egg”!

I think that as soon as Apple recognizes that there is a problem with these computers, the first thing it will do is make a change to the OS that reduces the maximum brightness limit allowed (to less than 500 nits). Time will tell…

Why does this happen?

For at least one of three reasons:

A design flaw — so this problem is likely to occur in a large number of devices;

A defect in components — the problem is limited to a few cases;

Use of components below Apple’s standards — the problem may be limited, or more widespread.

This was the explanation I was given. I’m not a technician. Only Apple will know the exact reason(s).

If I had to guess, I’d say that I don’t believe it’s a design fault, because Apple has an obligation to be very careful about that; I also don’t think it’s a fault with the component(s) because it seems to be happening all over the planet and doesn’t seem to be localized; so I think it’s due to the use of component(s) below, or at the limit of, Apple’s standards which, when put under extreme stress (higher brightness), end up failing.

I think it’s already clear to everyone that this is a design or manufacturing defect in this Apple model.

So let’s hope that Apple takes on this construction problem and repairs it or at least contributes part of the cost of the (overly expensive) repair of our computers.

If it were a car, surely all our computers would be called into the workshop to replace the component that has broken down or is in the process of breaking down.

As it’s a computer… let’s hope that Apple will behave in a way that suits its customers, who believe in the above-average Apple standard…

So keep presenting your cases to Apple.

Since I’ve been out of the tech loop for a few months this year, maybe this issue has already been discussed. Anyway, here are a few scattered thoughts.

My first reaction was to add this to the series of duds in Tim Cook’s Apple (see my previous post to better get what I’m alluding to). It’s true that Apple is not new to this kind of problems. Several iterations of past MacBook Pros were plagued by graphics card issues that rendered the computer basically unusable. And some Intel iMac generations met the same fate, unfortunately. (I really feel for my brother-in-law, because his previous iMac — a 21.5‑inch 4K iMac from 2013 or 2014 — was exactly one of those with graphics card issues).

But while “Jotap62” above says that they don’t believe it’s a design fault, I’d say this is very much the case. Apple wanted to redesign an already-slim-enough iMac to produce something that was strikingly thin for a desktop computer. The space inside such a thinned down chassis is so tight that Apple had to make the power supply external to the iMac, just like a laptop’s AC adapter. When you work within tight spaces and with strict tolerances, things can go wrong. 13- and 15-inch models of MacBook Pro manufactured between 2016 and 2017 presented an issue with the display flex cable. As explained here, in those MacBook Pro models, the flex cable connecting the display to the board is now wrapped around the hinge and is a spring-ed ribbon cable. This makes it even more susceptible to breakage over time due to the constant tension and relaxation when opening and closing the lid, unlike the previous design, where the wire connecting [the display] was tucked inside the hinge cover and never moved.

This issue also surfaced in the ultra-thin 12-inch retina MacBook models, as if the butterfly keyboard was not enough of a blunder.

Now, back to the iMac display issue, as the technician contacted by “Jotap62” explains, if the iMac’s display flex cable “has to sustain a very high voltage (around 50V) to power the LCD (this despite the iMac’s power supply being 15.9V)”, I find it hard to believe that none of the hardware gurus at Apple didn’t know that. I’m not an engineer, nor a hardware guru, but what I suspect is that those responsible of designing and assembling the innards of the 24-inch M‑series iMac were given the daunting task of fitting everything into that super-thin chassis, and something got to give. And this kind of flex cable was a compromise, the ‘okay-enough’, ‘it’ll last enough’ solution.

What infuriates me is that this is the kind of problem the manufacturer certainly knows about, but they also know it won’t trigger immediately. Customers then are faced with a costly out-of-warranty replacement, where the right thing to do would be to treat this as a known manufacturing issue and offer a free replacement. (Especially considering that — and this is the other infuriating bit — even after a replacement the issue is likely to reoccur). Maybe it’s also a case of components that are below Apple’s standards or requirements, but the outcome is the same — customers shouldn’t pay for these mistakes.

But this would be very costly for Apple, I already hear some say. Well, no one asked them to make this stupid, unnecessarily thin iMac redesign in the first place.