Chosen Solution
Hi, I have recently picked up one of these old beasts and want to do a bit of a project on it to see if I can get her going and if so how fast I can make the speeds. This post will pose quite a few questions So to begin I plug this Mac in and power it on and hear a few sounds and vibrating “brrr” kind’ve sound and can hear a few things spinning up. I don’t get a Chime and the screen remains black. The fans are quiet but do turn as I get cool air coming out when I put my hand at the top. So if anybody could offer some trouble shooting steps about problem solving the boot I’d appreciate it. I’ve heard of resetting the NVRAM, PRAM. I haven’t done these but I do plan to. I believe I have reset the SMC. Since I have done research and have found that the logic board is potentially the reason I can’t get it to boot. I also realize that I cannot upgrade to the iSeries processor and to do this I must change the logic board to one of the newer A1312 boards. But first I must get it running to see what needs fixed and what doesn’t. I have been doing quite a bit of research regarding an old mac I picked up and have discovered the only way of unlocking some more CPU power is to change the logic board to allow for Intel iSeries processors. My question is has anyone actually successfully switched to one of the newer A1312 logic boards? If so was there any hiccups or quite severe drawbacks. Secondly would I need to get a new GPU? or would the one out of my current EMC2309 iMac be compatible? Same as the ram is it plug and play compatible also between the logic boards. A good explanation of what isn’t compatible would be greatly appreciated. And any links to in depth guides on the process as I couldn’t find any. Also, the logic board I’m looking at swapping with is from this model iMac Here TL;DR : I have a 2009 27” A1312 iMac and it doesn’t start. I have reset the SMC and plan to do the NVRAM and PRAM. I need some steps about howto get it going as I’m familiar with Windows machines but not Apple machines but am eager to learn. If the logic board is broken I want to upgrade it to one of the later A1312 boards. First I must get it going. Thanks, Jacob
Update (03/16/2020) @danj Hi Dan! I’m back having replaced the logic board with the iSeries one you suggested and an Intel i7 processor. I got the parts really cheap as the guy who sold it said the CPU fan ran at full speed and it was given to him like that so he sold it for parts. Where would I start troubleshooting for something like this? The CPU fan sensor is plugged in correctly and in MacFanControl it reads at 0rpm it will be silent for about 8 minutes then when the processor gets warm the fan will go at full speed. Thanks, Jacob
Jumping between major designs is not really doable. Apple alters too many things so the newer logic board won’t fit within the older system and many cables aren’t going to fit (length & signal). If you look carefully the location of the connectors on your board are all neatly on the top edge the newer boards have them scattered around. But there is a glimmer of hope! This is a transitional series! The A1312 (EMC 2309) iMac10,1 is a Core 2 Duo and the A1312 (EMC 2374) iMac11,1 is an Intel I Series either an i5 2.66 GHz or an i7 2.8 GHz. That is the board I would go with to push this to the max. 27” EMC 2374 logic board Apple P/N 661-5428 The A1312 (EMC 2390) iMac11,3 was a major design change and won’t work in your system. This board can support 16 GB of RAM with the correct SO-DIMMs and while it only has a SATA II (3.0 Gb/s) HD interface you can install a SATA II supported drive like a 2.5” Samsung 860 QVO. Do consider the costs and the limitations this system has as well as the highest OS it can support is macOS High Sierra (10.13.x) Update (03/11/2020)
Here’s a breakdown of the onboard diagnostic LED’s: LED 1 - Indicates that the trickle voltage from the power supply is detected by the main logic board. This LED will remain ON while the iMac is connected to the AC power. The LED will remain on even when the computer has been shut down or put to sleep. The LED will turn off only if the AC power is disconnected or the power supply is faulty. LED 2 - Indicates that the main logic board has detected proper power from the power supply when the computer is turned on. This LED will be ON when the computer is turned on and the power supply is working correctly. LED 3 - Indicates that the computer and the video card are communicating. This LED will be ON when the computer is communicating properly with the video card. If LEDs 1 and 2 are ON and you heard the startup sound, but LED 3 is OFF, then the video card might be installed incorrectly or need replacement. LED 4 - Indicates that the computer and the LCD display panel are communicating. This LED will be ON when the computer is turned on and video signal is being generated. If the LED is ON and there is no image on the LCD display panel, the LCD display panel or inverter might be installed incorrectly or need replacement.
