CPU Upgrade Issue - No power
I decided to upgrade my 2017 iMac 27 in two parts this weekend: NVMe and SSD first, then CPU.
First part: 970 EVO NVMe with heatsink installed. Recognized @ Link x4 and great speed. SSD installed and MacOS Catalina reinstalled. Very happy so far.
Second part, a day after: Removed CPU, installed i7-7700k. Struggled a bit with heatsink like everyone it seems. But once done I felt confident that everything was done right, so I re-assembled everything. But the power switch didn't trigger anything!
- LED 1 is on as soon as I connect the iMac to the external power cord.
- Power switch cable seems intact and connected to PSU. PSU and logic board cables all disconnected/reconnected with great care and seem intact.
- Tried to short both power switch pin to start up the Mac. Nothing happened.
Does anyone have any suggestions or comments on what the problem may be?
- I've ordered a new PSU for safe measure. I can't find a spare power switch button (the only part available that has it is an entire empty housing!).
- Can't find a spare power supply control cable (between PSU and Logic board) for a 2017 iMac. But there are some for the 2011-2013 iMac which looks the same as for the 2017 version.
Tempted to order that. Does anyone know if the 2013 and 2017 use the same power control cable?
After discussing with friends, one plausible explanation could be that my CPU upgrade went bad. Such as static electricity frying the Logic board. Or the CPU is bad. Even though I've been careful all the way. However, if I understand the explanations regarding the logic board LEDs function, it seems that not even having the LED 2 or 3 on would mean my issue isn't yet entirely related to the Logic board or the CPU. Anyone can comment on this?
I would be very grateful for any suggestions (at least it'll boost my morale, as right now if the new PSU doesn't work, I would have probably to sell the iMac for parts!!)
Just received the new PSU (see picture). Installed carefully (making sure I discharge any static electricity from my hands prior). Reconnected all wires, after inspecting them (see picture). And unfortunately I have the same result: the power switch, which seems to be 100% intact (see pictures), doesn’t trigger any response. Fan doesn’t spin. No second LED.
Could it be the main power cable socket (buried under the bottom bezel of the imac housing)??
Any suggestions welcomed!
Disassembled the Mac again. Look very carefully for damaged cables, or sockets… None found! Took a picture of the wires coming from the main power socket (see below). Everything looks fully functional.
Could this be a back Logic Board??
I can finally breath: Removed the new CPU, installed the old CPU and I’ve got the board to boot up. Did not perform a full reboot with the LCD on. I will make another attempt at upgrading tomorrow with another CPU, so I had only the PSU and Logic board mounted.
Is this a Bad CPU or it wasn’t mounted right, I can’t say for sure. But the Fan started to spin at max speed without stopping, so that got me thinking and decided to go for the i7-7700 instead of the 7700k!
Now, I got to improve my tension spring loading technique. I concur with others that the tension produced by this spring is excessive (Judging from the residue of thermal paste which had been completely squeezed out to the sides when I removed the CPU). So I’ve kept a more important gap between the mounting spring and the logic board, than what I had originally measured (<1mm). See pictures.
Hopefully my next post will be about completing this job… Wish me luck.
Final update: Finally got the system to work.
How: The short answer is you have to unbend the metal spring underneath the CPU!
There is way too much tension in this spring, this put so much strain on the CPU that it bends it. Some pins are then no longer connected. When the LED 1 or 1-2 lit up and nothing more it just means that.
I’ve tried a i7-7700k twice, reinstalled the i5-7600, then tried and kept a i7-7700 finally. So I’ve got plenty of trials to figure all this out.
I will now answer questions :)
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So does your logic board work with all 3 cpus? My logic board doesn't work now that I upgraded to an i7 4771 on my 2013 imac.
из Tommy Tran
The issue is mounting the CPU is a bear! @sebmcadet issue was the tension of the spring and mounting the screws without distorting the CPU chip. This is where the method of tightening the screws is tricky! Just like replacing a tire you can't focus your effort on one screw screwing it in all the way before you do the others otherwise your wheel won't be mounted properly. You need to use a cris-cross pattern slowly tightening each screw down so the pressure is even as you go! Reducing the spring tension is a bit risky! The other risk is damaging the CPU chip as well if stressed
The other issue is having the CPU shift on you so you damage the socket pins!
i7-7700K works well on my 27" 2017 (I've replaced the i5-7500 3.4Ghz)
I have the same problem, the cpu edges bent a bit, but what exactly did you do to make it turn on? Until where do you have to tighten the 4 screws? Please help me
из Juan Barrios
Hey, look at my post down at the bottom, that's how I did it... need probably a bit of luck, too :-)
из Cirkmann Zirkel
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