Well I made a post not long ago trying to get one of my 20gb hdds to work, Had copied every thing in hex from original ms 20gb to my 20gb to find it didnt work and the firmware needed to be modified to reflect the details in the hddss.bin.
First method I tryed was using external programmer and pulled the chip and read the firmware.
Then rewrote the chip, That failed and killed one of my spare 20gb hdds. Think it came down to my soldering skills.
Next method I tryed was using one of the flash utlitys from seagates other brands of hdds.
That failed due to having to many checks on the firmware its going to write, I couldnt find and remove all them with a memory editor so gave up trying that way.
Next thing I tryed was using the tmos to change the info.
That apares to have worked, I managed to change the vendor, fw revision and LBA so it apares just like the original xbox hdd in the bios and when it checks with hddhackr.
Only problem is I should of checked this hdd actually worked first because when ever I try to write to it in hex edit to add the partitions and hddss.bin info it just gives cycle redundancy error. (think its the drive I replaced because it died) And I cant use the PCB from this on of the drive I messed up with soldering the chip on because they are too different.
So I am unable to test it on the xbox but it does look like it should work. I dont have any more spare seagate drives but next week I will buy a new drive for my laptop to replace the 120gb seagate in it.
Then I will have another seagate drive to modify and try that I know works.
Heres the basic instructions of what I did.
Made a TTL serial to usb adapter (same one I use for getting key off liteon drives)
Connect TX to RX on the hdd, RX is the pin next to the sata plug.
Connect RX to TX on the hdd, TX is the 2nd pin from the sata plug.
Other 2 pins are not needed.
Open putty to com of ttl serial to usb adapter.
Power on HDD.
Hdd spits out info into putty.
Then go into command info /C or Q depending on hdd.
Use the commands provided for what you want to change
Or look here and they have a list of commands.
Power off drive
Connect sata data plug.
Boot into dos.
Run hddhackr intill it says the bit that lists the drive vs the info in the hddss.bin.
Then went back to windows and opened it with hexedior to add partitions and hddss manually.
Will post again when I get another seagate drive to try (next week)
Feel free to try it your self if you have any spare seagate drives but be aware you might kill the drive.