The timing circuit in your control board is malfunctioning. The board needs to be replaced. My parts sources don't list the board, and I'm unable to find it on the internet.
I suggest you call Panasonic's customer service number at(NNN) NNN-NNNN They may have questions only you can answer.
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All the components on the control printed circuit board are mechanically soldered to it in a process called wave soldering. On occasion a circuit trace will not take as much solder as it should, a overtime a crack develops. The crack is extremely small, and with varying ambient temperatures, will make and break contact intermittantly. It would take an extended search with a microscope to locate it.