I have done tests on S9 12.5T and S9 Hydro 18.0T. Bitmain has started signing the latest firmware so nasties cannot get into the miner and change the config' to their own wallet address etc. You can recognise the signed firmware as it has a '.sig' or '.signed' element in the firmware file name near the end. If you flash up to this sig firware you cannot flash over to non sig firmware.
If you are an Antminer S9 Hydro user who was tempted to try non S9 Hydro firmware your miner will report errors in the kernel log. You will also see nothing much in the 'Miner status' and think you have fried or broken your S9 Hydro.
The resolution is to use t9+ -SD Tools.zip and unzip the file. You then get a folder and you copy the files in the folder (not the folder itself!) onto an SD card. You
DO NOT need to use a flashing tool such as balenaEtcher or diskimager.exe. It is just a plain copy and paste. Then put the SD card into your miner with it turned off, must be off!
S9 - Put the SD in upside down and change the JP4 jumper block to the 2 pins closest to the front of the controller card (the end with the Ethernet socket).
S9 Hydro - Put the SD card in the right way up (with logo or print upwards) and make a drawing or take a photo of the JP4 jumper block as it is. To make the S9 Hydro boot from the SD just remove the jumper block and put it somewhere safe.
Then for both miner types power up. Wait and wait until both red and green LED's (little lights) flash simultaneously NOT just once but continuously. This is the miner telling you it has used the SD card contents to flash over the chip contents.
Then power down. Put the jumper blocks back as they were originally and remove the SD card. With S9 the jumper block goes onto the JP4 pins furthest from the front. With the S9 Hydro just replace the JP4 jumper block onto the 2 pins that are closest to the edge of the controller card.
Your MAC address and IP will have changed. If it was a static IP it will now be dynamic. Use Bitmains own 'IPreporter' software. Do not forget to click the start button on the software and then press the 'IP report' button on the front of your miner. The IPreporter software will then return the ip address. Use this address in a web browser to access your miner. Don't forget if you make the IP address static, as soon as you do so, the web browser address is invalid; just type the new last octect in. EG: 192.168.1.134 as dynamic will change to what you state it to be when static, say 192.168.1.24.
Also your firmware will now be T9 based but at least I got you in. You can now use a backup or download an older non sig firmware and flash it up. You can always fall back on the SD card if you mess up. I advise you follow what Bitmain advises and use signed firmware. Sometimes it appears at the bottom of the list or sometimes at the top. Also, if you click on 'firmware' on the Bitmain site and see nothing, just scroll up. It's up top.
If you use Awesome miner SSH (elevated privileges) Putty or any SSH tool with a sig firmware it will keep its door closed and you will not be able to connect. With Awesome miner upgrade and you can use your Antminer GUI login name and password. Change them from root and root or root and admin to something else for safety. Also as previously mentioned do flash up to the signed versions even if you rollback to non sig unsigned versions for testing or different miner config' boxes available.
Links to....
IPreporter https://shop.bitmain.com/support/download?product=IP-reportert9+ -SD Tools.zip https://shop.bitmain.com/support/download?product=Flashing%20SD%20card%20with%20imageIt is 3 up from the bottom of the list.
Enjoy!
Please tip me with BTC at 3M3cEWUF81YBRQhL9eX9QdwAWRmfZoqU9W if I have helped you