It's been awhile, so (not surprisingly) I lost track of everything. This kind of troubleshooting is best done either all in a short time or by taking lots of notes. I dunno bout you, but I didn't take no notes.
I believe you said you had AC power at the relay contacts feeding your main power switch. To test what happens, you can use a neon light across the contacts. You may have one of those outlet testers (that you poke the probes of into your receptacle sockets to check whether they are live or not) laying around somewhere. If the neon light doesn't pass enough current to make things try to operate, you could start putting shunts across the contacts too. If the neon light illuminates, something is trying to draw current somewhere.
You shouldn't need to do this if TH02 is doing what it should. Previously you measured it at 40 ohms cold. This is OK for a PTC, as it is at its minimum value when no current is passing through it. As in a degaussing circuit, when power is first applied, the PTC will send a jolt of AC down the line. Naturally, much current will flow, heating up the PTC. Its resistance then skyrockets as it heats up, pinching off inrush current after a few milliseconds.
In this circuit, as the current falls, so should the PTC resistance. The voltage value at the bridge rectifier will end up hovering at a certain value while the relay it shunts is not energized. So in this unit, it looks like that juice goes through the bridge rectifiers and D07, out the brown wire, and up to the capacitor bank. I can't tell from the photos whether the brown wire is connected straight to the bank or if it goes through the fuse in the corner. Either way, you should be able to verify that path on your working unit when the unit is in standby to compare with the dead unit. If the micro is bootstrapped through the brown wire, it should have a certain amount of DC feeding the capacitor bank in standby. When the relay contacts close, and the unit runs, that brown wire will have full DC voltage from the bridge passing through it.
Whether or not the brown wire carries start-up voltage to the micro or not, if it doesn't match the working unit's behavior in standby, this would indicate a short or open (or wonky) circuit feeding off the main B+ capacitor bank. This could be anything. Main suspects include the tinychip, the power factor IGBT, the compressor control IC, etc.
A while ago, I found a few more resources, straight from panasanyo:
ftp://ftp.panasonic.com/heataircondi...andbook_sm.pdf
ftp://ftp.panasonic.com/heataircondi...2010-v4_sm.pdf
None of these resources really dig into the control board guts, as service techs are not factory service engineers. As these boards command the big bucks refurbished, I imagine the companies who bring them back to life have the tech sheets, prints, and diagrams secured in a data vault somewhere. they probably have a detail of internet police taking down any useful service info that finds its way out of the vault. Good luck finding anything specific without being an authorized service engineer.