Screen only works when connected to HDMI, OR Adobe Product running

When you where a kid did you ever play with electric trains… Setting up tracks in complex patterns using switches so a branch track could be engaged for your train to travel? Now this might sound strange ;-} The same logic applies here!

You see, your system has two graphics services the Intel internal engine and the dedicated GPU (think two start points), then we have two display outputs the internal and the external (the signal can be cloned to show up on both) and then to add even more complication we have three external ports! Two Thunderbolt and the HDMI port (eeny, meeny, miny, moe). Again, think about those model train tracks, which path you engage sends the train down (here the video signal).

Now the fun part different apps can also dictate which GPU service to use in this case the Adobe app is engaging the dedicated GPU. We could also have leveraged this app gfxCardStatus to achieve the same thing as well as force the system to only use the Intel internal graphics engine.

OK, so you got a better idea on this mess so where does that leave us… Your logic board has a problem within its switching logic between the different outputs. So far I’ve seen the issue related to how the Thunderbolt port needs an add a load so the upper circuit works correctly this is a known defect in the TB chip. I’ve also seen issues with the HDMI port being damaged.

In any case your logic board needs repairs or replacement.