TLTR; I already forgot this. Sorry to my late response.
Actually I’m using my iMac now for awhile now. I can say, 5 weeks from now.
In my deep observation, after I receive this error. I was thinking if the CPU fan was not working before my Video Card died and also damaged my HDD.
Please follow this link: White Screen of Death after booting up at Recovery Mode
So the case was, Before my VC died, I experience a heavy blower running on my iMac everytime I open it. So I have to reboot it and the blower will run back to normal state. Now, the blower that runs heavy here is the ODD Fan.
ODD Fan in my observation, is also the blower of the Video Card Heat Sink.
Now, after I ordered new CPU Fan here at iFixit including additional 8Gb of Ram (I have a thread as well for my RAM Upgrade), I started this thread in relying of might be the case was a defective CPU fan. But after running a System Diagnose this was the error. I am not a Mac Wizard Tech but I have a background of Computer Technician, so I have to evaluate everything going on here at my iMac to avoid very expensive costs to revived this machine.
- I test all the wirings and connections are all ok and responding = ok checked
- found some ground wirings are exposed due of the cover was breaking down = covered with electrical tape
- replace cpu/gpu thermal paste = ok done
- test all the fans if are all running fine = ok checked, except CPU fan socket
I deeply look to the board and see that there’s a little thing that “seems” busted, but I don’t see it clearly if it is busted or just a wire that got exposed. Overall I ignored it for now, I don’t want to go further to mess more the logic board.
Photo Fig. 1
(click the photo to see my red circle)
The final decision was a suicide logic board. But before that, I check and google if there’s a way to manually control the fan and see all the temperature inside hardware while I’m using the iMac. Yes there is. I download the copy of Macs Fan Control (google it and it is free).
Warning: This might be dangerous, but I do accept the risk and to risk my logic board (or even my iMac) if this experiment gone wrong.
I start the operation to tap the wire of my CPU fan directly to the wire of my ODD fan*.
After this successful fans wire tapping, I leave and observe the unit for a day or two without turning it off.
And it seems running fine. Though my initial investigation here was the fans that are oddly runs fast sometimes and sometimes not.
Here’s the condition I found:
ODD fan rely on the Optical Disk Drive temperature base on the sensor. And the CPU fan sensor also respond to the CPU heatsink temperature. Now, since the CPU fan wire was wired tapped to the ODD fan, the power supply that run to the ODD also get equally to the CPU fan. However, due of the sensor activity of the CPU fan, it filter the power**.
*I will upload soon a picture of what I did here.
**You will hear this fans loudly running if you will not configure your fan via Macs Fan Control app.
NOTE and WARNING: Again, I repeat. I do this in my own risk and have a background knowledge of what I am doing, if you are not expert or do not have a background knowledge, please consider buy a new logic board instead of this.