Moral of the story: S9 owners DO NOT upgrade firmware to 2019 version, you will lose SSH access!!!
I wrote that for a reason. Still, you could use an SD card to flash it back using that convoluted T9 firmware method, or simply boot Braiins OS and install that instead.
I don't think S9s should be running any other firmware at this point, unless you have the ancient controller.
With Braiins OS you can improve the efficiency from 100w per tera hash down to around 80w. This alone increased the lifetime of the units against Bitmain's wishes, which is why they responded by locking down ssh access since 2019.
Topic: Antminer s9 error "Cannot Find Signature!!!" (Read 449 times)
Thanks it works. 
If you flash the miner with the latest firmware and you trying to downgrade them back it won't work because 2019 firmware has new security they also disable your SSH access with this firmware.
Old version lower than 2019 firmware(2018 to 2017 firmware) doesn't have a signature that is why you are getting this "Cannot Find Signature"
Anyway, if you are planning to downgrade your s9 you can follow this S9 series (S9, S9i, S9j, S9 Hydro) Control Board Program Recovery
After that, you can flash it again with lower or older s9 firmware version.
Old version lower than 2019 firmware(2018 to 2017 firmware) doesn't have a signature that is why you are getting this "Cannot Find Signature"
Anyway, if you are planning to downgrade your s9 you can follow this S9 series (S9, S9i, S9j, S9 Hydro) Control Board Program Recovery
After that, you can flash it again with lower or older s9 firmware version.
How to solve this problem?
I'm getting this problem while upgrading with old firmware in Browser do you know how to fix this?
I have missing hashboard after I flash my s9 with latest version.
I'm getting this problem while upgrading with old firmware in Browser do you know how to fix this?
I have missing hashboard after I flash my s9 with latest version.
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