I have a 24 inch, mid-2007 iMac purchased used. I don't know the original owner and it's out of warranty.

On the display is a series of tan or yellowish horizontal lines - all an approximate inch apart, for a total of about eight or so. The spacing between is regular. They're wider (about an inch wide) at the left and right edges of the screen and taper to nothing at the middle of the screen. They are particularly noticeable on light-colored or white backgrounds, such as a Pages document, most web sites, etc.

I'm certainly open to disassembling the iMac and getting at whatever it may be (the onboard GPU?) that's causing the problem. In fact I have opened the machine for an HD replacement and fanned and cleaned, but to no result.

I also use smcFanControl to boost the fans, as I thought it may be poor cooling in the machine, but this has no effect.

Does any one have ideas or suggestions as to what is causing these discolored lines?

full display - tan lines


3 Answers 3


This looks like a backlight uniformity issue.

This is where the screen isn't being evenly lit by the CCFL bulbs behind it. Some of them are outputting differing amounts of light and cause this perceived 'discolouration'. The lighter colours really do show it.

Unfortunately, this is one of the disadvantages of a CCFL backlight system as opposed to something like LED backlighting - backlight uniformity can become an issue, especially with time.

You'd be looking at a screen replacement - outside of warranty, that's gonna cost you.

  • 1
    ^ This. No amount of PRAM resets or cable reseats will rectify the issue, I'm afraid. May 18, 2012 at 10:26
  • 1
    This does appear to be the problem, from what I can see online. Here's a guide from iFixit on replacing CCFL bulbs. I don't believe I'll endeavor on this but it's good to know.
    – wxs
    May 18, 2012 at 18:16
  • Definitely not a software issue. My old iMac (from around the same time) ended up the same, so I had to get an external screen because I was doing graphic work. The computer can still be used for non-graphic stuff though. iMac screens age. As the hardware performance specs also get outdated by the time that the screen gets into that condition, it's probably financially a better idea to invest into a new computer than to fix the old one. Unless you're very handy with hardware already and don't feel like opening the thing up and doing it by yourself isn't a massive and stressful unknown.
    – user158589
    Dec 12, 2015 at 23:39

If you boot the Mac holding the option key, this will have the firmware drive the screen and isolate any software corruption or odd driver bugs in most cases and let you know it's a hardware issue.

Usually vertical lines are the LCD failing - then a cable issue - lastly the GPU.

Usually horizontal lines are a cabling issue - then a GPU issue - lastly a LCD issue.

That's not to say you even have a hardware failure. Do post a picture and we can refine things based on the actual failure.

  • Thanks. I booted with Option pressed down and got the screen asking for which volume to mount from - the tan lines were still there.
    – wxs
    May 17, 2012 at 22:36
  • @bmike Do you know where the CCFL backlights are in that model? Could it be related to them?
    – Cajunluke
    May 17, 2012 at 22:43

Translation by google off the content above:

The lower plastic layer diffuser matrix is yellowing with time, and the lamp loses brightness, as a result - the common yellow color images and brightness differences (strip) from the brightness is insufficient. Solution - replacement of this layer, and preferably tubes. Analyze the matrix bands are clearly visible on this layer.

нижний пластиковый слой светорассеивателя матрицы желтеет со временем, а лампы теряют яркость, как результат - общий желтый тон картинки и перепады яркости (полосы) от недостаточной яркости подсевших ламп. решение - замена этого слоя, и желательно ламп. разбирал матрицу, полосы хорошо видны на этом слое

  • Hi Russian iBear, please use English language for the answer, I tried a translation with google translate, the output is poor.
    – bummi
    Dec 12, 2015 at 23:38

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