Why does motor comes on but brush head does not move

I have this issue as well.

The tear down guide doesn't go into the mechanical portion at the head of the brush.

I have mine open and there is an opening on the back inside that allows me to see some of the gears and they look functional. I can't figure out how to get in further to find the malfunction. Specifically, on mine, the metal 'pin' only vibrates. It is missing the up-and-down motion I recall from before.

I guess I can't add pics to the question as I'm not the op?

@scottbernardis

Post your comment as a new question on ifixit. That way you can add images.

Here's how to do this 기존 질문에 이미지 추가하기. It is the same procedure for a new question.

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Moderator.