No picture only sound

Sounds like the backlight bulb on the left is out. May need to replace the bulb, but do all of them at the same time.

T'Con board fault.
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/

Sounds like possibly it could be connection related between any AV/Cable ports. Worst case would be the capacitors of the motherboard leaking. It's possible to fix anything. Just make sure you have the knowledge and the right equipment.

Check the CRT ground wiring. I saw this on a computer monitor after I forgot to reconnect the wire from the ground line around the picture tube. It would start normally and fade out over a period of five-fifteen seconds.

Caution: pull the plug and wait several minutes, then check for voltage between the bare wires around the outside of the picture tube and chassis ground before you put you touch anything. If you get voltage, this is definitely the problem, and I've just saved you from a nasty shock (could be almost as high as 2nd anode voltage). If you don't get voltage, inspect at will.

One of your "X" buffer boards is defective. In Panasonic plasma tv's they are located at the bootom of the set and connect directly to the plasma diplay panel via a thin ribbon cable. The board you want to replace will be directly in line with the discolored vertival line in the picture. The part number is on the circuit board and usualy starts with "tnp..." or "txp..."

You can reduce the g2 for the blue tube
open the front grill and open the 4 screws hold the resister block
to have acess to the register block.
Then there should be the black box have 6 knobs
the one call for Blue g2 not the focus block.
Adjust it counterclockwise a little bit
and try turn on TV again

Sounds just like a loose solder connection. The trick is finding it. I would start with the microchips and the large transformer. Otherwise, it could be a capacitor starting to short out. I would give both options a 50-50 chance to be the problem.

So, where are the answers?

Bad technicians always say picture tube problem when the TV has black screen with sound. This a false statement and in some cases techniciacns use this to scare the owner or the charge a hefty amount. The truth is that picture tube outlast most component in the TV. If it will fail, it is gradual like the colors will fade or one or several color will be missing. This condition is the degration of the filament in the gun (CRT tv has three -Red, green , blue) I started to repair TV in the early 80's and only in one occasion that the Tube fail and it is a crack in the neck. For black screen with sound, the most common cause is the HV supply problem / Horizontal section. This can be caused by many things, like flyback transformer failure, horizontal outout transistor, horizontal drive, etc. For the cost-depends on where you are, in some countries labor is dirt cheap, in other ountries the parts are expensive.

I would have to say it does sound like the CRT is reaching its end. The thing that points this out that the picture gradually gets a little bit better as it warms up. It most likely isn't worth the cost to fix it.