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.
Bu iyi bir soru mu?