i have finished this trail. the result is same. BT is lost. whether the t520 do not support the combo card(BT&Wlan)?
Note: previous backup_tools were being run with secure boot disabled already. (I dual-boot Linuxes on this laptop) I attempted flashing with USB formatted with MSDOS and FreeDOS, in case either made a difference. pflash reported "FileData checksum error" and "Erase failed!" as errors, and after rebooting, the BIOS version is still on 2.57, not the 2.55 version I would expect if the flashing had succeeded. I guess that means no joy?
Ah, sad times. I don't have the skills to do surface-mount resoldering work. Guess I'm stuck with the couple of old wifi cards that lenovo approved for the laptop, for ever. :/ Thanks for your help in trying stuff out, though.