A1708 - What should I do, if system is overheating and black screen.

Let me start off with the short answer you don’t want to hear: Replace the logic board!

Now the long answer…

Find the schematics and board views for this system (locate the 820-???? number on the logic board).

Watch Louis Rossmann’s YouTube vids on how to diagnose logic boards.

Test your systems power rail circuits using your bench power supply & DVM and USB-C power meter. Use a high speed storage oscilloscope to review the output signals making sure they are present.

Then you’ll need to have the micro soldering tools to desolder the bad components and find replacements and then soldering them on.

Conclusion

By the time you bought all of this gear and the hours of debugging the logic board, it would be easier and cheaper just to … (insert the simple answer)

Or, find someone who has already made the investment ands the skills letting them to the work. That maybe not an option for you as you may need to ship your system to them.