If its tripping its most likely to be the magnetron which would make it uneconomical to repair.
If you have a multi meter, with the power disconnected you can strip the unit down and then check the two internal fuses. If the fuses are fine, disconnect the two spade terminals on the magnetron turn on the timer and see what voltage you get across the two spade terminals. If your not seeing a high voltage then it will be the main board at fault, if your seeing a high voltage its the magentron which isnt powering on when the current is applied.
However on looking are eSpares and buyspares websites they dont list your model, so you may struggle finding replacement parts, however based on my experience a replacement Magnetron would be the region of £250.
Good afternoon, I just wanted to see if I can be of any further assistance, I would appreciate if you could rate the service received.