iMac won't start up. No diagnostic LEDs. PSU tested fine (see . below)
By the way, the model I have is the "late 2015" that shipped with i5-6500 processor. This is the skylake processor family.
The iMac was working condition yesterday. I opened the iMac to replace the processor and replace the HDD. I chose the best processor compatible with this model: i7-6700K.
When I put everything back together and tried to power on, it won't come on. I do hear a small clicking sound when I plug the power plug in to the outlet (this is probably a spark when I insert the plug as its localized to the output, and not near the PSU). I do not see any diagnostic LEDs turn on even when plugged in.
1) Measure AC inlet cable, showing 120.8volts
2) Measure the PSU supply rails. There's 4 solder points, but only 2 are marked. GND and +12v. When checking these solder joints I can successfully measure +12volts between GND and the +12v rails. I also verified that the cable (12 pin?) also measures the correct voltage.
3) I checked the power button itself, and when I press it I can measure almost 0 resistance between the cable's two contact points (indicating that the power button is working fine.
4) I checked the PSU signal cable that connects to the logic board and I verified that each rail/wire is correctly connected and not shorted or damaged.
5) I checked RAM seating and tried different combination of slots and testing 1 at a time, and 2 at a time.
6) I checked voltage of the battery under the logic board (measures 3v).
7) I opened everything up and examined the CPU socket pins. There was some mis alignment I could see in the iPhone's magnifier feature and I corrected that. And reseated the CPU and still got the same behavior.
8) I put the old CPU back (i5-6500), same result.
Any help is appreciated! I am trying to isolate the issue, but can't seem to figure out how to find the problem part. Any steps about testing the PSU would be appreciated.
Cette question est-elle utile ?