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I have an iMac 21.5" 2.7 GHz i5 (Mid2011) Product number: A1311Model: EMC2428Video Card: AMD Radeon HD 6770M A couple weeks ago, when booting, there are vertical white/blue lines on the screen and can not enter into OS X GUI. I sent my iMac to the Apple Shop to identify the problem and was told that the video card has problem. They stated they could not provide video card replacement service because the system is too old or very high cost. So I decide DIY. I checked eBay, there’s a few sellers selling AMD Radeon HD 6770m. They charge more for 6770m than the AMD Radeon 6750m. Could someone kindly tell me if can I use 6750m to replace 6770m as its cheaper?
Well… The issue is performance! The cheaper board is not as powerful as the more expensive version. Here’s the IFIXIT guide: iMac Intel 21.5" EMC 2428 GPU Card Replacement For reference here’s your choices: AMD Radeon HD 6750m, 512MB - Apple P/N 661-5944AMD Radeon HD 6770m, 512MB - Apple P/N 661-5945 You do need the Apple version of the board as these have custom firmware on them. Specs: AMD Radeon HD 6750mAMD Radeon HD 6770m Update (04/07/2018) These GPU boards are for the 27" iMac. The problem is the heat sinks these use is a different configuration and offer more cooling than the one in your system. While some people have retrofitted them into there 21.5" systems they tend to burn them out as the system just can’t cool them effectively. I would recommend you stick with the correct GPU board that came in your system. Besides these are more expensive! AMD Radeon HD 6770m, 512MB - Apple P/N 661-5967 (same as above different heatsink)AMD Radeon HD 6970m, 1GB - Apple P/N 661-5968AMD Radeon HD 6970m, 2GB - Apple P/N 661-5969 Specs: AMD Radeon HD 6970m, 1TB or 2GB
