Plasma has flickering, ghostly picture

More than likely you ruined the HDMI circuit. Over twice the required voltage is never good.

Fault to the main power supply regulator section. Either it will be a separate board, or the part of main board. Check and replace damaged component/s at its main power regulator [SMPS] section circuit. Contact any service technician. If you wish to get some details; check the site linked here. Surf the site with patience. Pull up older posts.
http://electro-medical.blogspot.com/
It will be best to replace the power supply regulator board as card basis rather than making "Surgery" to it; which usually will make loss for both money and time. Even though you can make it right, it will cost around an amount equal to the cost of a new board; including the cost of (spare parts + service charge) More to say, most of the spare parts to it will be difficult to get from open electronic spare part market. This is true to most of the flat panel TV power supply boards; irrespective of its brand and screen size.

Flickering can be adjusted. To get more details; just Google for the site "Electro help". There is more details about how to rectify this fault. Surf the site with patience.

Sounds like main board fault. Contact any "Experienced" service technician, or, the authorized service center for Viore.
Gopakumar Gopalan Google

There are many reasons for the flickering screen to a PDP. If you wish to get more details about this, check the site lined below. Pull up older posts there, either by its left side bar, or see it in Timslide option. http://electronicshelponline.blogspot.com/. It is difficult to enter all of those here by this window.

check first at the sound set up menu might set to off. if the settings is ok and the speaker is also good, the cause is either bad amplifier circuit or sound processor at the main board. at this time you will need a trouble shooting.

The tv was working fine until this morning, then the picture went out but the sound is still working.
TV is only 3 years old, no real electrical problems

it is the y-sustain board that has a blown fuse.. it is problably the one on the left. by replacing the fuse wont solve the issue, you need to replace the whole board.

The power board has definitely failed. Sounds like a short that could be causing the cracklin sound.
http://www.shopjimmy.com/sanken-3501q00201a-power-supply.htm
I have ordered from this place before with fast shipping and no problems.
Hope that helps.

@ findmeifucan
PDP42V18HA is plasma tv and it has nothing to do with convergence nor it has convergence stage / option.