I wanted to renew the thermal paste on cpu and gpu. i removed the screws from motherboard. but the part on the back side of GPU broken 2 capacitors on motherboard. I became aware of this problem when lines appeared on the screen when I started the apple imac. The part I mentioned broke the capacitors and I could only find one of them.
this is the pic of the caps
https://disk.yandex.com.tr/i/aM0FD6hHmkdFtg