Chosen Solution

My macbook’s main display has mostly horizontal pink lines that flash within certain fields on the screen that are otherwise normally white (browser windows, text fields, etc.) It happened spontaneously and without warning a week ago. The display was fine one minute, then suddenly the pink appeared. My external display that runs out from the laptop is unaffected. Also, applying pressure to the underside of the laptop (pressing in between where the two fans are) stops the issue on the main display. Would love suggestions on how to fix it? My laptop is a 2009, but I’d like to get a few more years out of it. Only recent changes to it where the installation of mavericks about 6 months ago and a ram upgrade made at that same time.

Pressing on the case does not make sense here given the fact you state the external monitor is AOK. Assuming the external monitor image is good all of the time I would focus on the internal monitor signal pathway from the GPU to the LCD its self. Often I replace the complete lid assembly when I get these types of issues as the driver logic on the back of the LCD unit or the LDVS cable has become damaged. While it is possible to disassemble the lid to get to the LCD and/or the LDVS cable you do end up damaging a few parts in the process and can also break the cover glass if you are not careful. Did you bang or drop your system as some point or did it get wet or sit in a puddle of liquid? You may just need to clean the logic board and/or LDVS connector & cable end on the logic board. Follow this IFIXIT guide MacBook Pro 15" Unibody Mid 2009 Logic Board Replacement from the start to step 6, then jump to step 20 and stop there. Make sure you have an ESD mat & wrist strap and the proper tools. To clean the logic board (or any spots that need cleaning). Use a can of Can’ed air a soft painters brush to wipe the dust off, and use distilled water (not tap!) with some cotton swabs (Q-Tips) and lastly, some good quality Isopropyl alcohol 85% or better. Wipe the surfaces with the a slightly damp swab with water first (if needed a few times) then go over them again with the Isopropyl alcohol. The alcohol acts as a drier here pulling the water from underneath. In any case make sure things are fully dried before powering up.

None of these solutions worked for me unfortunately. So for others still struggling with it, what did work for me was re-calibrating the display colours:

  1. System preferences
  2. Display
  3. Calibrate
  4. Continue
  5. Un-check “use target white point”
  6. Move the bar until the lines disappear. Hope this helps!

There was a simple solution in my case. The screen looked pink at certain times of day - hint, hint. Go to System Preferences > Display > Night Shift, and if it’s on, turn it off. I had turned it on with good intentions, but the color shift from sundown to sunrise seems far more drastic on a laptop screen than it does on an iPhone. I hope this solves your problem, too.

I also have the same issue, and yes applying pressure to the underside case corrects this issue. This failure appears randomly. I have iStat and on the fan specs I have switched from Auto to Medium. I believe it has to do with poor cooling management. Somebody should open extra vents at the bottom of the case. Update (12/01/2018) I also experience the same problem. I have addressed a solution with iStat, modifying the fans from AUTO to MEDIUM, this has helped me reduce the pink horizontal lines appearing. I do find the venting of the MAC most deficient. Just the airing inlets in the back of the MAC in my opinion are not enough!

I had this issue while updating the system version. The story goes like this. I need to update my system. The machine has been bugging me to update for weeks. I remove external monitor and power move laptop to other room. Closer to WiFi. I start up ate. It seems to proceed OK. About twenty mins later the screen is black I restart the laptop. I get the pink lines restart again. I get the system updating loading screen twenty mins pass. I see this string about the pink lines. I think is have a video issue. I’m planning a trip to the &&^&^$^ apple store I move laptop back to the other room plug in external monitor and power Loading screen appears on external monitor with some time left on the up load The upload completes i get normal working screens on my laptop and external monitor !!! im not sure what happened. Perhaps I caught the updating in mid update so it showed the pink lines. Not sure.

you have a problem with GMUX chip. Perhaps it is LVDS connector. To sure diagnose press lightly with your finger on LVDS connector, when image become clear, it is the LVDS cable.. and you must clean it with alcohol and fine brush.when you press lightly the GMUX chip and lines dissapear, then you must exchange this chip. This IC has a solder joints problem, that after years fall connection between chip and Logicboard, so it must be reball, or exchange and programmed(from old one) with new one..