I believe the S9 has a single PCB temp sensor which is TMP451, it seems like it's slightly hidden under the heatsinks, you could probably still see it without taking the heatsink off, according to a post in one of the Russian mining forums, pezhvak identified the temp sensor location in this post


Image Source =forum.bits.media (I used a hyperlink because the URL is in russian and result in a very long string).[/size][/size]

If the information provided in the post isn't accurate, please let me know, I can ask someone who probably knows.