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"no drop pulse on pm_pwrbtn_L when triggering smc_ONOFF_L"
This points to SMC issue.
But keep in mind, PCH can still block the SMC to make its job correctly.
Changing SMC is the next step.
However, check first signals and voltages for U5000 (2 OF 2) at page 36.
Just in case, try to start in SMC bypass also.
This board magically started up while I was poking around and now consistently starts. I reflowed the SMC regardless and gave it a love tap. No boot. I couldn't get my EZP2019 to flash a new bios to the chip so I swapped bios from different board and it now boots but running high fans so guessing may need cleanME which I'm not sure I'm going to be able to do. The chip appears to be a Micron 25Q064 which isn't an option and none of the "close" options are working either.
Replacing the battery seemed to calm everything down. Tested over and over and it seems to be holding up. guessing heating board up and reflowing the SMC brought it back to life and the battery needed to be replaced for it to be back in full working order.