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.
![](https://ip.bitcointalk.org/?u=https%3A%2F%2Fforum.bits.media%2Fuploads%2Fmonthly_2019_11%2Fimage.png.8b36c90dfb47f6398c82ba58ca978030.png&t=662&c=aeHDnsVKLovhSQ)
Image Source:
forum.bits.media (I used a hyperlink because the URL is in russian and result in a very long string).
If the information provided in the post isn't accurate, please let me know, I can ask someone who probably knows.