Can a witness at a hearing be found incompetent to be a witness because of mental incapacity?

Appellant now argues that he was incompetent to be a witness because of mental incapacity. His counsel, however, made no objection as to his competency as a witness at any time during the hearing and the objection must therefore be deemed waived. (People v. Berry (1968) 260 Cal.App.2d 649, 652-653, 67 Cal.Rptr. 312.) Nor do we find merit in appellant's claim that his speech handicap necessarily made him an incompetent witness. As previously noted, a ward attendant who was very familiar with appellant's speech served as an "interpreter" and there was no contention made at the hearing that this arrangement was unsatisfactory.