Pressure canning dried pinto beans, 7 quarts for 90 minutes. My range top malfunctioned and the 90-minute timer still had 9 minutes to go. After cool down period, all jars sealed. Will it be safe or do I need to pitch it?
The functioning of the stove (and heat input) matters less than the pressure and temperature maintained in your canner during those 9 minutes.
If your dial/weight jiggler indicated that it was at correct pressure for your altitude during those 9 minutes, then the 240F steam temperature needed for canning was properly maintained, the beans are safe and properly processed.
The full lethality time at pressure and cooling down is needed to guarantee safety for the products based on the researched and validated product processing tables - for those unfamiliar, refer to USDA's Complete Guide to Home Canning (chapter 4, p. 4-5 for dried beans).
If there was any doubt regarding processing time, as @Joe said there is a safety margin built in to the processing schedules for home use, but safety as validated isn't guaranteed. It's easy enough to fix within 24 hours with reprocessing, there's no need to discard - refer to this answer for more: My jars sealed, cold packed raw chicken quarts, but canner ran dry towards the end. Can I reprocess within 24 hrs when my new canner arrives?
With reprocessing you'll end up with perfectly safe but mushy beans though, so you may want to reprocess with added ingredients as baked beans.