What is causing my Chihuahuas scabby ears?

It all started (I think) when he was bit on the tip of the ear about a month ago. The scab is still there and quite large and thick. It's not healing. Now he has several little scabs on both ear flaps (pinna). These are not localized on the tip/ edges of the ear so I do not think it is mange. He also has clean ear canals. I'd love to hear some opinions before taking him to the vet.