iMac 27 Late 2015 no power after hdd upgrade

[whack0]

Hello,
I'm new to this forum so please bear with me... Anyway, I installed a new 2TB drive on my iMac 27". I plugged in the display to make sure that everything was okay before I applied the adhesive tape, but it won't power on. There are no sounds from the drive or fan, but there is a bank of 4 LED's on the main board and one is on. I've tried unplugging it and holding down the power button for a minute and then plugging it in again but still nothing. I've been super careful during this process so I'm stumped as to the cause. Any help would be greatly appreciated. The model is listed below. Thanks.

iMac 27" Late 2015 :MK462LL/A A1419 - 2834

 

[DeltaMac]

If nothing at all happens when you press the power button, recheck your connections.
The power button plugs in to the logic board very close to the hard drive, so you may have accidentally disturbed that.
Look at the top left corner of the logic board - again just under the hard drive.
There's a tiny connector (4 wires, maybe even 2 wires, not sure), which is where the power button is connected.
Try reseating that connector.

The single LED that comes on when you first attach the power cord tells you that the power supply has power.
When you press and release the power button, another LED (plus the fan) should come on immediately, then a third LED when the display turns on.
The 4th LED is probably an overheat indicator, and you should NOT see that one come on, unless there's a problem.

 

[whack0]

If nothing at all happens when you press the power button, recheck your connections.
The power button plugs in to the logic board very close to the hard drive, so you may have accidentally disturbed that.
Look at the top left corner of the logic board - again just under the hard drive.
There's a tiny connector (4 wires, maybe even 2 wires, not sure), which is where the power button is connected.
Try reseating that connector.

The single LED that comes on when you first attach the power cord tells you that the power supply has power.
When you press and release the power button, another LED (plus the fan) should come on immediately, then a third LED when the display turns on.
The 4th LED is probably an overheat indicator, and you should NOT see that one come on, unless there's a problem.

First, thanks for your quick reply! I'm unsure of which connector you're referring to as there is no logic board directly under the HDD. My camera is charging but you can refer to the hires image in step 7 of this website for a reference:

https://www.ifixit.com/Teardown/iMac+Intel+27-Inch+Retina+5K+Display+Teardown/30260

Again, thanks for your help.

 

[whack0]

You were correct, reseating the power connector on the logic board was the problem, however now it chimes but there is no video!!! The display cable and power cable are seated correctly and I have 3 LED's lit. Google isn't my friend right now. I thought the nightmare was over...

 

[tubeexperience]

There are three cables you need to check:
display power cable
display data cable
power button connector

 

[whack0]

There are three cables you need to check:
display power cable
display data cable
power button connector

Hi! I've checked all three cables and as stated I now get sound but no video output. Not sure how else to troubleshoot any further without a service/repair manual. Could I have damaged a connector since I'm only getting 3 lit indicators?

 

[tubeexperience]

Hi! I've checked all three cables and as stated I now get sound but no video output. Not sure how else to troubleshoot any further without a service/repair manual. Could I have damaged a connector since I'm only getting 3 lit indicators?

Check the connectors for bent pins.

 

[Fishrrman]

OP wrote:
"Anyway, I installed a new 2TB drive on my iMac 27". I plugged in the display to make sure that everything was okay before I applied the adhesive tape, but it won't power on."

That's one of the hazards of being a "do-it-yourselfer".
Take the risk.
Be prepared for the possible consequences.

Wouldn't it have been easier to just plug in an external USB3 drive...?

 

[Floris]

Back in the day, I read a few times that some iMacs won't boot back up after hdd if the thermal sensor on the drive needed to be replaced as well, say .. going from hdd to ssd.. I am not familiar with this at all, for all I know this isn't true. But, if there is a sensor on that hdd and you didn't reconnect it, maybe it wont on a fail msg? Just thinking outloud here, sorry if I am wrong.