Retina display detected but no video

Hi Folks,

It 5.1 Model with a retina, touch bar, and T2.

My son replaced the screen in an authorized repair center, which didn't work initially. Long story short, after visiting apple, they booted the same system with the same screen. ( I don't remember precisely the issue, but it was something to do with retina verification). The system did work for about four months. However, when the battery ultimately died, it returned to the same issue. (i.e., black screen).

Now when I connect via external display, I see os detect the Retina and read all retina display specs. So I clean the display connecter on T-CON. Cross-check both black cables on T-CON going to display. It is brand new. I disconnected the battery and booted without a battery to reset SMS., which didn't help. Run apple diagnostics. It shows no error.

Is there any log I can check to verify what OS does? For example, does apple do anything fancy with T2 a and retina display, and if yes, can I debug it somehow?

Thank you,
Mus