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F90 means that your door latch has failed and the door isn't locking properly. That is why the cooktop won't work as well since the latch thinks it's stuck between the locked and unlock position. Try to open the door and wiggle the little latch hook. Flip the breaker off or unplug the oven for 60 seconds. If it still doesn't work, you'll need to replace the door latch before you can use the oven again I'm sorry to say.
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