820-3302 distorted image

[PPVCC_S0_CPU]

I have imac late 2013 that's having distorted image when os loads up, it will have normal screen with apple logo and loading bar on start up, but screen gets all fuzzy and distorted when os loads up, even on hdmi output the screen is distorted, it works fine when put in safe mode.
can it be gpu? And is there any way to fix it? I can't even think a way to measure voltages on it.

 

[2informaticos]

Should be GPU, as the problem appears even on external display.
You can heat/reflow it, just for test.
However changing it is the only way to discard it at 100%...