I have lg 47 tv that sud pic stop has sound when you turn on you see a light for sec

Yes you can do-it-yourself its sounds like the Back light led's in the back of the flat screen are not getting power. it could be 1 of 2 boards inside the chassis of the TV look online and put that model number in when you look.

Take it to a TV repairer, preferably an LG authorised repairer. It is highly unlikely it is the power supply. There is nothing you can do to fix this yourself.

Probable main power supply failure; the power indicator is supplied by an 'always on' low voltage supply so (when normal) it allows the remote to turn on main power.

Your tv T-con board is defective.

If audio [sound] is OK, and the fault is with only picture, check and replace damaged component/board, at its back-light section circuit. Gopakumar Gopalan Google

More than likely your power board is defective

To clarify, your TV is working correctly, since you get sound and video from all devices - Only your PS3 has no sound or video?

If your PS3 was previously used with regular AV cables (Red/White/Yellow) then you most likely need to do a PS3 video reset t output video over HDMI.

With the PS3 OFF, press and continue holding the power button until it turns on, beeps twice, and then turns back off. Do not release the power button during this process.

You may have to try the video reset a few times if it doesn't work right away.

After video reset, you should get sound and video over HDMI.

We had the same problem of pathetic sound quality and volume with a sony brava. Thats just the way they make tv's these days because most people buy a surround sound system as well. We bought logitec computer surround sound speakers for about $140 and plugged into the ear jack, problem solved, we have heaps of volume and stacks of bass.

3 blinks corresponds to convergence ICs
http://home.earthlink.net/~oleg.filippov/ConvergenceFix.htm
http://cmpalmer.blogspot.com/2006/11/fixing-my-own-tv-part-ii.html