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iMac 2013 CPU Upgrade

titaniumjones

titaniumjones

macrumors member
Original poster
Oct 29, 2011
30
4
Help!
I don't know if anyone is still reading this thread. This is what happened to me and what I have done so far.
iMac 2013 27" 3.5GHz Nvidia GT780M 4GB (This may or may not be important)

So the hinge failed on this machine and, knowing my way around the iMac and other machines, I decided to change it myself. Having purchased a new hinge and the required strips to reseal the machine once I'd finished I proceeded with caution.
Everything went smoothly.
New hinge in place I though - well whilst I've got it stripped downs so far, I may as well replace the thermal paste with some Arctic Silver 5. So I took the heat sink off, cleaned it up and reapplied.
On this model you have to put the CPU in the socket put the 'gunk' on. Put the heat sink on and then invert the whole logic board to insert the screws and spring from underneath.

Disaster! The CPU slipped and I wound up crushing the edge of the chip!

**** **** ****

Don't panic, stiff upper lip and all, lets get a new CPU before my wife finds out.

Amazon to the rescue. Now I found this thread and looking at the costs and delivery times I purchased the 4790 (Not the K) instead of the 4771 that was shipped in the machine.

Put it in and reassembled. Put in the power cable - 1 light. Pressed the start - 2 lights ..... ..... ..... ..... .....

So I understand that
LED 1. Trickle power
LED 2. Start button pressed - Main power on
LED 3. GPU found
LED 4. LCD found

So, I draw the conclusion that the mother board is damaged. (Seems logical to me). Ebay to the rescue. 4 days later a new mother board arrives with no CPU. i've just spent the afternoon switching the motherboards and CPU.

Put it in and reassembled. Put in the power cable - 1 light. Pressed the start - 2 lights ..... ..... ..... ..... .....

Exactly the same result as the old logic board. So maybe the logic board is not damaged after all. Now I have (apparently) 2 functioning logic boards and 1 CPU and they don't want to play.

Can anyone shed light on this?

In total I'm down over £600 and still don't have a working machine. Worst I don't know why.
Trying to predict the questions that may come.
Light 1 on when power cable connected
Start button pressed
Light 2 comes on
Fan spin up
Light 2 goes out
Fan stop
Light 2 comes on
Fans start
HD spins up
Fan spins faster
Fan reaches take off speed......
 
In the iMac I believe LED1 is trickle power. LED2 comes on when the machine has proper power to the logic board (power on pressed) and indicates a functional power supply. LED3 means the iMac and the GPU are communicating. LED4 indicates proper communication between the logic board and the LCD panel.

If you are not seeing LED3 then it sounds to me like the video card might be the problem, either improper installation or GPU failure.

Alternatively, if LED2 is coming on and then going off, you might have a bad power supply.
 
SaSaSushi said:
In the iMac I believe LED1 is trickle power. LED2 comes on when the machine has proper power to the logic board (power on pressed) and indicates a functional power supply. LED3 means the iMac and the GPU are communicating. LED4 indicates proper communication between the logic board and the LCD panel.

If you are not seeing LED3 then it sounds to me like the video card might be the problem, either improper installation or GPU failure.

Alternatively, if LED2 is coming on and then going off, you might have a bad power supply.
Click to expand...

Hi SaSaSushi
I don't believe it is a dodgy PSU, Once light 2 comes on, goes off and comes on again, it stays on. Mu understanding is that means PSU is ok.
I also thought it meant the GPU is damaged. On this model the GPU is fixed to the Logic board and not on an MXM card. Replacing the Logic board also replaced the GPU

Any other ideas greatly received.
 
I'd advise you to remove the CPU in order to check the alignment of the pins for any problems.

Also, as a valuable troubleshooting step, I'd put back the original CPU to see if that works.
 
Hi SasaSushi,
TBH the CPU has been in and out of the computer 3 or 4 times. There is no damage to the contacts in the socket. The old CPU (4771) is bent! it is definitely busted. When I did put it into the system (Aligned correctly) Nothing, absolutely nothing happened. I just got the trickle power LED illuminated. No fans no HD nothing. So I'm pretty sure that that chip is toast.
As to the new CPU (4790), I'm beginning to think that there is some compatibility problem, but looking at the tech specs, I can't for the life of me see what may be preventing this chip from being accepted by the system board.
 
titaniumjones said:
As to the new CPU (4790), I'm beginning to think that there is some compatibility problem, but looking at the tech specs, I can't for the life of me see what may be preventing this chip from being accepted by the system board.
Click to expand...

I think you are on to something there. According to Everymac, the top of the line for the Late 2013 was the 4770s.

You need to use a CPU supported by the firmware of the system and the OS. I've read similar reports of problems from users who attempted to upgrade pre-2017 iMacs to Kaby Lake processors.
 
SaSaSushi said:
I think you are on to something there. According to Everymac, the top of the line for the Late 2013 was the 4770s.

You need to use a CPU supported by the firmware of the system and the OS. I've read similar reports of problems from users who attempted to upgrade pre-2017 iMacs to Kaby Lake processors.
Click to expand...
Unfortunately, I think I have learned a hard lesson.
I did believe that if you kept within the series everything would be OK. Both the 4771 and the 4790 are Haswell processors and (almost) identical.

I've upgraded processors in the past in a 2006 xserve and a 2009 xserve, both went smoothly. But not in this iMac.

Still hoping someone can confirm.
 
Another good place to ask/look for iMac hardware upgrade questions is the iFixit Answers page.

That said, from what I've read the logic board firmware for the iMac will only support CPUs used in a specific iMac generation.

For example with the 21.5 inch iMac:

Late 2012 = 3770
Late 2013 = 4771
Mid 2014 = 4790K
 
The CPU needs to be supported by MacOS for power management. Since the 4790 isn't officially supported this is likely your problem.

I would recommend sticking to CPUs of that iMac year. While I would love for you to try a 4790K, it does have a higher TDP (88w vs 84w) so if there was a alteration of the heatsink with the 5k iMac (4790K was in the 5k iMac btw) you could run into throttling problems. I would selfishly love to see you try it so I could potentially do this upgrade in the future. :)

I think your best options will be another i7-4771 or if you want to save a bit the i5-4670. You lose 100mhz clock and hyper threading with the 4670 but the difference will only be noticeable in very slow and heavy CPU intensive task. Even though my usage revolves around video transcoding I couldn't quantify the difference between those two (10-15% benchmark difference, 5-10% real world) for more than 50 bucks.

Potentially your problem could be solved by modifying files (i7-4790 has been used in Hackintosh's) but that is outside of my realm of knowledge. Not sure how you could accomplish that at this point either, maybe pulling the drive and using another Mac?

Good luck, keep us posted. PM me if you try the 4790K route! Lol
 
titaniumjones said:
Unfortunately, I think I have learned a hard lesson.
I did believe that if you kept within the series everything would be OK. Both the 4771 and the 4790 are Haswell processors and (almost) identical.

I've upgraded processors in the past in a 2006 xserve and a 2009 xserve, both went smoothly. But not in this iMac.

Still hoping someone can confirm.
Click to expand...

Did you manage to fix your Mac?
 
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