My Panasonic (Matsushita) convection oven/microwave, model NE-9910P is now showing an error code of FF FF when I press Start. It accepts the time & power programming inputs, but when pressing Start, the inside light comes on for less than one second and the seconds display are shows "FF FF". This oven is also known as a "Dimension 3," manufactured in 1984.
The FFFF error code shows whether using microwave or convection functions.
It has had the magnetron replaced once, about 12 years ago.
"The 'FFFF' display is a common problem in older Panasonic convection ovens. The problem is the temperature sensor thermostat located on the top rear of the oven. This is the convection temp. sensor for the correct oven temperature. Replacing this open sensor will correct the problem."
I will try to get the spare parts next week and see if it works. Hope it helps you too.