For $29/mo, we provide access to advanced level technicians who will answer your questions on any Macbook board related matter to the best of their knowledge promptly & walk you through how to solve your problem so you can deliver a working board to your customer.
Not too much to do on a Mac Mini, apart of power problems, or BIOS.
And GPU change, when you suspect that.
As no schematics available, must use datasheet, or part of MacBooks/iMacs schematics, which use the same IC where you need to work.