The reasons for the lack of sound can be divided into two conditional parts: the hardware (problems with hardware) and software. In some cases, you can try to solve on their own, without resorting to the workshops.
The solution of software problems
If the tablet's operating system is Android, go to "Settings" and find "Sound". Go into it and try to adjust the volume. If the sound did not appear, in "Settings" go to "backup & reset" select "Reset settings". This will reset all user preference settings, and the PC will return to the factory configuration. After that, the unit should restart. Note that you should not select "erase SD card, otherwise you may lose saved data on the flash drive.
If the tablet operating system Apple iOs (iPad) after completing all the above steps in menu "Settings" also check the "volume Limit" in the submenu of "Music".
The solution to hardware problems
Independently search for and Troubleshooting of the components of the tablet is recommended for those who are even slightly familiar with electronics. Persons not confident that they'll at least be able to disassemble the PC, it is better to consult specialists.
Disassemble the apparatus. Given that all the tablets have their nuances, pre-read the instructions. After removing the case to find the speaker. Most often it is soldered to it and 2 wires, usually of different colors. Sometimes a speaker can be attached to the rear of the tablet and just adjacent to the contacts on the Board.
Check the continuity of wires suitable for him. In the presence of discontinuities solder them. If the wires have no breaks, carefully desolder the speaker and check the resistance using an ohmmeter. Serviceable speakers have some resistance (different for different models). Faulty have either zero or infinite resistance. You can solder your speaker to any other device to the headset and thus to check his work. Can be soldered to the Board like the characteristics of serviceable speaker and thus verify the integrity of the chip of the audio codec. Repair of this chip requires special equipment and cannot be performed at home.