It is not a matter of figuring out, in order to find what is wrong you need a special Test Bench.
In addition, if you would find the problem and it entails replacing components on the printed circuits I doubt that you would find the components on the open market. And any case most of these components can not be replaced manually.
Most computer devices are built by Robots, that is why so delicate work can be done and, it inexpensive.
When you send a unit to repair and the trouble is on the printed circuit they take out the whole thing and put in another one.