Mac goes on and stays on/ on and off / white screen with power on but nothing ealse -
I have experienced them all and : gpu reballing did not helped so :
Between cpu and gpu there is an intel chip ( sla5t ) well i tought i will give it a go and it worked :)
In 3 out of 5 it was 100% fix but in other 2 not really so i replaced them completly with new ones and all fine till now .
Good luck with fixing and you can always go to : www01tech.co.uk
Dont take it as 100% solution, motherboards are very complicated, symptomps can be same but different solutions.