What is Set top box , what is Inside A Set Top Box (STB)

A set-top box (STB) or set-top unit (STU) is an information appliance device that generally contains a TV-tuner input and displays output to a television set and an external source of signal, turning the source signal into content in a form that can then be displayed on the television screen or other display device. They are used in cable television, satellite television, and over-the-air television

 After Unscrew and remove the cover of box.

here it is the inside view
which containing Electrical components
chips, Ic, capacitor, crystal oscillator, transistor and all other components.

Here is the full open view of the Circuit Board