It could be The Little Warranty People by Eduard Uspensky, originally published in 1974 (Wikipedia, Russian)
The warranty people, small people who live in and take care of
appliances under warranty, must defend themselves against a curious
little girl and an army of mice
There is a News Man, living inside the radio set.
And there is a very curious girl (not a boy), that saw once those "little warranty people" and so tries to find them again (but it seems she never disassembles the radio).
News Man is also referred as a Radio Man, and he is repairing all kinds of a radio devices. He has a radio set of his own, and it is actually disassembled (without a box).
Full story (Russian)