It can be seen from the question you asked that you have a certain foundation in electronics, but electronics (applied electronics) is too widely used in our life and work. You must read some books carefully. Of course, if you need to know the circuit diagram in that field, you must read books in that field.

For example, the circuit of the TV set you mentioned is divided into: power supply part/tuner part/intermediate frequency amplifier/video detector part/same part separation part/line field scanning part/high voltage part/sound circuit/color decoding circuit, etc. This requires you to understand the principle of TV first, then check the physical components on the board, check the secondary circuit and get familiar with it. Then you will know which components are probably used when you see the circuit board of the TV set.

The above is an example of ordinary CRT TV, but most of the circuit principles of LCD /PDP plasma TV are different from ordinary CRT TV, which requires you to read some books on this subject.

Another example is MP3 player, whose circuit principle is completely different from the above products. If you want to know about MP3, you must read some books about it.

If you have some electronic basics, it won't be too difficult to teach yourself.

But if you don't have an electronic foundation, you have to go to a vocational technical school to study. To tell the truth, electronics (including maintenance and design) can't be done without formal learning.

Finally, I wish you success in the electronics industry.