iMac 27 with no video problem and cause is logicboard help.

[Pragmatiko]

Hi all,
as a title i have that iMac with no video issue.
I have tested the follow parts:

- graphic card tested is ok
- ram tested are ok
- power block tested is ok
- inverter tested is ok
- display tested is ok
- bios tested is ok

Whet turn on no start audio and no video.
What i can still check?

Thank you very much.