Get the MODEL number from the pdp (display panel), for the mfg and the generation of the panel, i.e. lg pdp42vxxxx. Get the numbers from the y and z boards on either side of the pdp.
Search the web for common faults of that panel/board, you may have to use google translate to read foreign tv forums, where most of the component level plasma repair discussion is.
On the HP PL4260N (LG pdp42) I have, had no pic w/sound, blown fuse on ysus. Checked y and z board fuses for open, FET's ,IPM (stk) under the large heatsink for shorts. Problem was short in stk795-820, difficult to remove without damaging traces. 795 series stk's starting to show up on ebay and in parts.
Mitsubishi WS-55513, Philips 55pp9352/17