Sharp R-957M Combination microwave oven

[FlyingBrick]

Have a Sharp R-957M combination microwave oven that always runs at around 30 degrees centigrade lower than the actual temp set on the display. On pre heat with the grill on it does reach the correct temp and then switches off the top grill, but once the grill is off then the actual air temp measured inside with an accurate Comark Electronic Thermometer settles to around 27-30 below the setting on the panel across the whole range.

Have checked the temp probe in the top of oven which reads 358K ohms at 15* centigrade and cleaned the contacts to the plug on the main pcb. Fan heating element reads 40 ohms.
As there seems to be no adjustable pot to adjust the reading to the panel setting is there a SOT resistor that can be changed in value to bring on the fan heating element to a higher temp before switching off?

Anybody with some clever ideas on setting up the temp in the actual oven to the setting on the panel. Had thought of playing around with a pot connected to the temp probe wires.
This oven is not a customers so happy to play around with components on the pcb.

Chris

[Author]

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