Is the PS4 showing signs if it has a hardware defect?

I would like to know if no matter which part of the Ps4 is broken there's always a sign of a defect. Say for example graphics card broken = graphic error or something. Or are there defects where you do not notice it directly? Because a buddy of mine in some games sometimes short jerks, and I want to know if this may indicate a defect. Otherwise, nothing is noticeable on the ps4 to recognize what can be interpreted as a defect.

When hardware breaks down, it's a sign that the console is not working anymore.

Ruckler may indicate a slow disk. You can easily exchange them.

But if the CPU, GPU or Ram breaks, the console simply does not work anymore.

So it does not work anymore, you think it's just not working? So it can't be broken except for a slow hard drive?

This is definitely the most likely. Otherwise, the console simply would not work anymore.

So if a hardware is defective, the console would not go at all? No matter what hardware defect?