iMac gives little fan spin when power button is pressed

I’ve got an iMac 2011 27 inch with 3.1 Ghz i5. I bought it with knowledge that the gpu is dead. So I opened up the iMac and powered it on, so that I can see the diagnostic leds. The first led is on and the second led blinks for a second when te power button is pressed (sometimes I have to hold the power button for a few seconds).

At first I thought the power supply was bad or some voltage regulators. But after some testing I found out the the gpu was making a short or something. I found this by unplugging everything from the logic board except the power button to see if maybe a component was making a short. That’s when I saw the second led turn on and gave me the hope that the power supply isn’t dead.

After that I plugged everything in except the graphics card. And after I have pressed the power button, I heard the boot chime. So I bought a new gpu (Nvidea GTX 770m derived from a dell).

I am planning to flash it so that I can get a boot screen and control the brightness of the screen.

The only concern is that not something on the logic board is conflicting between the gpu and power supply. But I have to test that out. Also I haven’t fount this issue anywhere else online, so I thought I would share my experience, so maybe if someone else has the same problem I could help with this posting.

I will update this post when I have my new gpu and tested, expect it to be updated around a few days.

Also here is a link to a video I uploaded how the iMac first behaved with the gpu installed: https://youtu.be/F6VH7_d3uLg

And here is a link of the succes I got with the gpu uninstalled: https://youtu.be/C-bqN3wPD9M