If you’re thinking about buying an iMac this holiday shopping season, there is one reason why you might want to hold off on that purchase. Several people who bought an M1 iMac a few years ago have reported a major problem with the display–a problem that doesn’t appear until after the standard warranty expires.

A Macworld reader researching an M4 iMac purchase brought this Apple Support Community thread to our attention. In the thread (which has 352 “Me too” votes), several users report that the M1 iMac screen shows horizontal lines that hinder the screen’s usability. The users report that the problem appears over a year after the M1 iMac was purchased, and since the standard warranty has expired, the user must pay for the repair, which can cost $650 or more in the U.S.—about half of what a new M4 iMac will cost.

User Jotap62 said they had a technician look at their problematic iMac. They determined that the problem lies with a power cable for the LCD, which can wear out over time due to the high amount of voltage running through it. Because of the way the LCD is constructed, the repair requires the whole LCD to be replaced, which makes it quite expensive. And even if the repair is done, there is no way of knowing if the problem is permanently fixed.

A few users reported that Apple fixed the problem for free after the standard warranty expired, but it took some convincing. They gathered the information reported online (including the Apple Community thread) and took the issue up with an Apple Store manager, who decided to fix it. We’ve contacted Apple to see if they’ve addressed the issue and will update this article if we receive any new information.

The M4 iMac was released only a few weeks ago and the M3 iMac was released a year ago, so those models haven’t been out long enough for the faulty cable to burn out–if those models are still using that same cable. There’s no way for users to know if that’s the case.

Presumably, this problem would be covered under AppleCare+, which costs $60/£60 per year or $169/£169 for three years of coverage. Though we don’t usually suggest customers buy AppleCare+ for a desktop Mac due to the lack of travel, it’s something to consider if you’re buying an M4 iMac, at least until we find out if the problem has been addressed.