No volume on my 50 ' plasma hdtv

Check all the COF [Chip On Film] connection for any loose connection to its socket/s. If you wish to get some details; check the site linked here. Pull up older posts. Surf the site with patience. http://electronicshelponline.blogspot.com/
Line, faults & possible causes to LCD & Plasma screen are given with illustrations. You can get an idea about the fault to an extent.

Try resetting via the on screen menu.
What is tv connected to?

It's obviously beyond your expertise to repair it yourself. And it's not the sort of problem that can be diagnosed over the internet.
Find a trustworthy repair shop and take it there.

Based on what you have tried if a buzz or loud static via the speakers you have something wrong in the audio output circuit of the set--problem here is that circuit may be part of the Main board that processes all signal---a look inside---following the speaker leads back would lead you to that board.

A simple thing to do to narrow it a little (you may have done this) is with sound all the way off put your ear to the internal speaker--hear anything at all like a deep hum?

Depending on age of set and cost of the board likely bad it may or may not be a do it yourself repair.

SD TECH

That, I would guess, is a decoupling problem in the decoding section of the audio stage, or a poor connection in the audio section. Unfortunately a service manual and engineer will be required to find the problem
Hope that helps.

Test on the audio output amp for a tone, check on speakers, if there is a tone you have a front end fault which could be the audio processor. If ther is no sound connect from the audio output to an amplifier for an output.Then you are lucky.... Hope it works.

pcb key control must be replaced

Do you get sound on Audio Line-Out pins of LG TV?
You can check sound at Audio Line Out pins by connecting any Amplifier / Home Theater system. If TV has sound out at Line Out terminals, then Output Amp is defective in your TV.
If there is no sound on above said pins, then its some thing complicated and needs service manual to rectify.
Good Luck.

please follow the steps below:

TV
RED + SELECT (flashes twice)
TV
0056

try the volume if this works then press SELECT to save the code. If not then press TV again then the volume. repeat this step until the volume works then press the SELECT button to save the code.

cheers

Little Dish Fitter