Hi @jxk90c ,
It appears as though there is a problem with the magnetron circuit in the oven.
The magnetron is the component that produces the microwaves that cook the food.
In saying this it doesn’t have to be the magnetron per se that is the problem, it could be anything in its power supply circuit i.e. HV capacitor, HV diode, HV transformer, door interlock switches or control board.
All of these components are used to operate the magnetron whereas for convection cooking a heater element is turned on which only needs the control board to apply the standard AC power supply to operate and regulate it.
I cannot find a circuit diagram for the oven online which would help to narrow it down but sometimes there is one to be found on the inside of the oven cabinet. Having it would help tremendously.
Be safety aware if you decide to open the oven to check for any obvious problems. The HV capacitor can store >6000V DC for months even if there has been no power connected to the oven for this length of time. It needs to be discharged correctly as soon as it is accessible after removing the oven cover and before commencing any other work inside the oven. This amount of stored voltage can seriously injure you or worse. If you don’t know what you’re doing then don’t do it!
If you decide to open the oven and after the HV capacitor has been discharged correctly I suggest that you first check that the door interlock switches are all functioning correctly. I am not familiar with your particular model so I’m not sure if the switches are used when the oven is in convection mode or not, but they most certainly would be when the oven is in microwave mode as they are an important safety feature. They prevent the microwave oven from starting if the door is open and shut it down if the door is opened whilst it is operating, preventing harmful microwave radiation escaping from the oven cavity. With the door shut the oven cavity becomes a Faraday cage
Here’s a link to the parts for your particular model in case you find a faulty part. There are other suppliers online that may suit you better. Just search for JE1590WC01 parts to get results.
If opening and checking the oven seems too daunting, contact a reputable, professional appliance repair service and ask for a quote.