I would not agree that Sanyo's support sucks based solely on the fact that they refuse to give you technical details.
if you need the schematics I can probably find them for you, but I bet you this is not the only thing you will ask for.
Supporting others is what really sucks because the reward for helping someone is having another 10 people coming for help.
And basically one of a 100 will consider paying for what they receive in return.
Consider this: a power surge may have hit the power, but may have also struck through the data cable.
The TV could have one or both of its main boards defective - the power board and/or the main board.
You start by making sure the power board produces all the voltages it is supposed to produce and if it isn't then you know you have a problem there.
As you may have seen this is actually a Panasonic power board and if you're in the industry (or if you do some research) you'll find that power boards are the Panasonic's weak spot just as Y-SUS boards are known to be bad in many LG plasma TVs and buffer boards are known to be the culprit of many Samsung TVs.
Long story short, I'd test every power transistor on that board for a shortage and I'd try to manually power it up to see where it fails.
There are usually 3 stages of activating a plasma power supply: 1) standby voltage (front LED present; always on); 2) main board and amplifier power (PS_ON); and 3) display sustain power (VS_ON).
If all that sounds too complicated then what you need is to go eBay and buy the cheapest board 1AV4U20C52300 that you can find.
Before doing so, though, make sure that's the same board you have in your TV.
Sanyo releases completely different models under the same model identifier and DP42740 may not even be a plasma at all depending on the chasis.
Hope this helps...if it sucks I guess I can at least consider myself Sanyo support level :-)