Hi K.Apiwatc
Thanks for your suggestions, i thought so that i need to format the unit ha ha. I've a few points to confirm before i proceed
Option 1
Since i've a full clean original backup of os version 4.4 from another 4190T
1. Could i downgrade my unit to 4.4 and replace "all" files from the original backup ?
2. I read from some where that there are file(s) that keeps things like HW version/id or someting like that that shouldn't be replace, if this is true what's the file(s) name ? (so that during step 1 i could obmit replacing it)
3. Once done continue with convert to 1490 3.00 TH

Option 2
Format the unit (I think i don't have a clean copy of 4.90 us backup)
1. Backup the current software on the unit (with corrupted files)
2. Format the unit (Fat 32), Reboot, webupdate+install all additional update, Reboot
3. This is the part that i'm not sure if i copy files (without replacing files exist on the unit) from step1. would the files with problem be transfer over to the unit ? (or those problem files already be replaced during the format & updating process)

Another question which may not be related, i've read some where that it's possible to simulate upgrading/downgrading using usb flash drive, i can't recall what folder/files that needs to be present on the flash drive before doing the simulation also could this simulation be done using the webupdater ?

Thank You
Happy Chinese New Year To All