Some of these gets marks between LCD and diffuser and shows up as smudges in the lower left and right corners of the LCD. I guess humidity or fan circulation patterns somehow draws debris in here. Just fixed a late 2012 A1419 (27") Unfortunately didn't take before picture.
Video
Here is a video of later 4k/5k screens. Basic process is the same but assembly of various years probably slightly different such as the 2012
Removing the 27" LCD
Many guides available. Adding additional detail on the bottom edge where its most difficult and people have experienced glass cracking there.
Used typical plastic pizza wheel tool to cut the taped down glass+LCD assembly. 27" is bigger and therefore more fragile than the 21.5". Pizza wheel can't cut the bottom edge and after reading ifixit comments cracking the bottom by the usual method tilting up the screen, was particularly cautious here.
Tried to pull from the corner tabs. One tab got 1/2 way and the other ripped. Maybe due to laying iMac on its back and display weight on the tape. Might be easier standing.
Gradually tilted slightly to loosen the adhesive. Never past 30 degrees. Lined the bottom edge with thin plastic cards for protection. iMac aluminum chassis does have thin black tape lined on bottom to protect the glass. Best to add additional protection while tiling and loosening the adhesive.
Bent a small corner on the plastic card to cut the tape starting from the corner. Small bend cut maybe only 1/2 width of the tape. Bigger bent corner to cut remainder. Go slow and avoid high force. Use different L bent depths to cut gradually.
Disassemble LCD
Remove tape and screws along the perimeter
Separate Glass+LCD from Diffuser
Lift up metal tub slightly from bottom to separate.
Turn over LCD (be careful, no more screws+tape holding the sandwich together)
Lift up glass + glued on LCD to expose surfaces between LCD and nearest diffuser. Clean these surfaces. Its hard to expose these 2 surfaces lifting up the metal tub as there is heavy plexiglass like diffuser block in the way.
Reassembly
Before reassembly, align 2 diffuser sheets into their slots
Re-Taping the Screen
27" are quite challenging. Many people have had theirs fall off in few days to months resulting in cracked glass. Here are some possible solutions. Not sure which works well
sites.google.com
After all done, looks good as new
Video
Here is a video of later 4k/5k screens. Basic process is the same but assembly of various years probably slightly different such as the 2012
Removing the 27" LCD
Many guides available. Adding additional detail on the bottom edge where its most difficult and people have experienced glass cracking there.
Used typical plastic pizza wheel tool to cut the taped down glass+LCD assembly. 27" is bigger and therefore more fragile than the 21.5". Pizza wheel can't cut the bottom edge and after reading ifixit comments cracking the bottom by the usual method tilting up the screen, was particularly cautious here.
Tried to pull from the corner tabs. One tab got 1/2 way and the other ripped. Maybe due to laying iMac on its back and display weight on the tape. Might be easier standing.
Gradually tilted slightly to loosen the adhesive. Never past 30 degrees. Lined the bottom edge with thin plastic cards for protection. iMac aluminum chassis does have thin black tape lined on bottom to protect the glass. Best to add additional protection while tiling and loosening the adhesive.
Bent a small corner on the plastic card to cut the tape starting from the corner. Small bend cut maybe only 1/2 width of the tape. Bigger bent corner to cut remainder. Go slow and avoid high force. Use different L bent depths to cut gradually.
Disassemble LCD
Remove tape and screws along the perimeter
Separate Glass+LCD from Diffuser
Lift up metal tub slightly from bottom to separate.
Turn over LCD (be careful, no more screws+tape holding the sandwich together)
Lift up glass + glued on LCD to expose surfaces between LCD and nearest diffuser. Clean these surfaces. Its hard to expose these 2 surfaces lifting up the metal tub as there is heavy plexiglass like diffuser block in the way.
Reassembly
Before reassembly, align 2 diffuser sheets into their slots
Re-Taping the Screen
27" are quite challenging. Many people have had theirs fall off in few days to months resulting in cracked glass. Here are some possible solutions. Not sure which works well
Macs Stayin Alive - HW Tips
2009-2011 iMacs ( 11,x - 12,x ) Important dis/reassembly info on these iMacs are here https://sites.google.com/view/imac-metal-gpu/imac-hw-tips
After all done, looks good as new
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