Just wanted to share the experience I had today upgrading my 2011 27" i5 2500S to an i7 2600. Might help somebody in the future...
I bought the used i7 on eBay and it arrived here (Sweden) from Poland. I disassembled the iMac (which I've done several times over the years) and installed the i7 with some new thermal paste, then refitted the logic board in the chassis. I also took the opportunity to remove the optical drive, because I never use it and I wanted better airflow to the bigger graphics card that I recently put in. Once all the logic board connectors were back in, I decided to power up the iMac before fitting the LCD, just to check everything was ok. I was met with three status lights on the logic board, but also a endlessly repeating (about every 1.5 seconds) start-up chime/bong. "Oh sh*t" thought I. A brief search showed surprisingly little online about this boot problem and not much consistency in what was there, most of suggesting possible RAM or boot disk problems. After checking all the connections, I concluded the new CPU must be to blame and set about refitting the old one. Same result. "Oh sh*t" again. I then tried reinstalling the original 6770M GPU, but that didn't work either. Eventually, after quite a lot of time and frustration trying different things (putting the OD back, various RAM modules, disconnecting and reconnecting stuff) and becoming increasingly sure that the new CPU (or something I’d done) had killed the logic board, I decided to put everything back together and continue another day. And of course... once the LCD was back on, the iMac (with the new CPU) booted up perfectly! So good news in the end, but I wish I'd tried refitting the LCD as a first step in the troubleshooting, rather than two hours later…
I bought the used i7 on eBay and it arrived here (Sweden) from Poland. I disassembled the iMac (which I've done several times over the years) and installed the i7 with some new thermal paste, then refitted the logic board in the chassis. I also took the opportunity to remove the optical drive, because I never use it and I wanted better airflow to the bigger graphics card that I recently put in. Once all the logic board connectors were back in, I decided to power up the iMac before fitting the LCD, just to check everything was ok. I was met with three status lights on the logic board, but also a endlessly repeating (about every 1.5 seconds) start-up chime/bong. "Oh sh*t" thought I. A brief search showed surprisingly little online about this boot problem and not much consistency in what was there, most of suggesting possible RAM or boot disk problems. After checking all the connections, I concluded the new CPU must be to blame and set about refitting the old one. Same result. "Oh sh*t" again. I then tried reinstalling the original 6770M GPU, but that didn't work either. Eventually, after quite a lot of time and frustration trying different things (putting the OD back, various RAM modules, disconnecting and reconnecting stuff) and becoming increasingly sure that the new CPU (or something I’d done) had killed the logic board, I decided to put everything back together and continue another day. And of course... once the LCD was back on, the iMac (with the new CPU) booted up perfectly! So good news in the end, but I wish I'd tried refitting the LCD as a first step in the troubleshooting, rather than two hours later…
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