As best I can tell, the PIC16F819 is a general purpose microcontroller,
https://ww1.microchip.com/downloads/...Doc/39598F.pdf . Perhaps it is being used as a supervisor.
Your 5VSB is working. The problem is in whatever circuit enables the main inverter, its controller, or in the main inverter itself. Since I lack a schematic, I suggest tracing the enable signal path to find where it stops working or there is some other circuit keeping the inverter disabled.
I suggest making a list of the ICs' part numbers in the P/S and seeing what each IC is. For example, an LM339 is a quad comparator and an LM358 is a dual op-amp.
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PeteS in CA
Power Supplies should be boring: No loud noises, no bright flashes, and no bad smells.
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