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Hi and welcome to JustAnswer,Thank you for the question and your patience. Should you still need assistance for information purposes only...Initially, it would appear to possibly be a main board issue as the power supply seems to be working and the panel is priming. Proposed preliminary tries (if have not been done):
The idea is to allow the built-in diagnostics to track potential suspect(s) / circuit failure.
A friendly reminder: most Service Mode settings are critical. An unnecessary/wrongful configuration change may and would render the Panasonic TH-42PZ80U completely inoperable.
Hi again Chris,
Surprised that the Service Mode did not work as that is as prescribed by the Service Manual for this model. Similarly, am surprised that there is no blinking LED that would also serve as an error indicator.
With this in mind, then 2 course of action; a lengthy check of present/missing voltages at each board or replacement of a likely failed board. The latter would serve then as both an attempt of a fix and as a test by process of elimination.
Please post back how you would want to approach this and/or should additional information be needed.
I realize that the above information may perhaps be not what was expected. Unfortunately, there is no quick-n-easy fix and neither is there a workaround; sorry for having to be the bearer of bad news.