Firmware Tcl 20b -

| Issue | Solution | |-------|----------| | SP Flash Tool shows “ERROR: STATUS_BROM_CMD_SEND_DA_FAIL” | Reinstall VCOM drivers, try different USB port, use USB 2.0. | | Phone not detected | Hold Volume Up/Down while connecting, or remove battery if possible. | | “PMT changed for the ROM” error | In SP Flash Tool, go to “Format” → “Auto Format Flash” → then flash again. | | Stuck on bootloop after flash | Wipe cache/data from recovery (hold Power + Vol Up at boot). |

A: The bootloader is unlocked, or the verified boot chain failed. Re-lock the bootloader via fastboot (fastboot flashing lock) or re-flash stock firmware. Firmware TCL 20B

The TCL 20B uses a standard A/B (Seamless Updates) partition scheme. Critical partitions include: | Issue | Solution | |-------|----------| | SP

| Partition | Function | Size (approx) | |-----------|----------|----------------| | xbl | Secondary bootloader (Qualcomm) | 3 MB | | abl | Android Bootloader (UEFI-based on QC) | 1 MB | | boot (A/B) | Kernel + ramdisk | 64 MB | | vbmeta (A/B) | Verified boot metadata | 8 KB | | modem | Baseband firmware | 120 MB | | vendor (A/B) | Proprietary drivers (HALs) | 500 MB | | system (A/B) | Android OS (Go edition) | 1.5 GB | | userdata | User apps & settings | Varies (32/64 GB) | | persist | Calibration data (WiFi/BT/audio) | 30 MB | Note: The TCL 20B does not have a

Note: The TCL 20B does not have a separate recovery partition; recovery is embedded in the boot image (ramdisk-recovery).