First check to make sure there isn't a mute switch or switched to external speakers, then
use ohmmeter to measure the speaker resistance (3ohm to 30ohm is usual).
Now find the speaker wires, and follow them down to the pcb, and look for a chip with
7/8 legs then measure the voltage on all of its legs, you should get 8v to 20v on one pin and half of that on one of the others, the internal circuit of most chips is that of a push/pull output stage, with the output coming from the middle of the pair of transistors.
(if there is no chip then it will actually be a transistor push/pull pair).
If no voltage of at least 6v then look at the pcb from each leg of the chip, and look for an electrolytic cap to earth, thats the power line,
so follow it and look for a voltage regulator or straight from power stage (PSU),
and test if voltage there.
check for fusible resistors and power diode and smoothing cap.
If voltages are ok, then when your meter (other probe hanging loose) probe touches the input pin ,a buzz from speaker should sound, if not then change chip.
if buzz occurs then your looking for the SIF chip,
so look for a three legged Xtal filter with 6mhz (5.5mhz europe) thats the chip.
Is the eeprom/micro pro set to a different country sound system ?
Is the mute line on ? micro pro control
Is the speaker switch set to internal ?
Is there power to the output chip ?
is there at least one pin (on the o/p chip)with about half the power voltage ?
Is there power to the sif chip (12v) ?
Is the tv from another country (different xtals) ?
Hope this may help you;