A1369 RAM issues

I have a problem with this card, it presents the classic problem of graphic artifacts due to ram, I reballed much of the ram but I just mitigated the problem after about half an hour of operation under stress, the artifacts reappear, how can I check the memories and figure out which one fails?

The problem may be on CPU side, not the RAM chips.

So the CPU is gone? I started from a black screen with three beeps then this situation

Is the classic problem.
You may waste the time changing all RAM chips and same issue came back.