If you installed a malicious APK that wrote to the system partition, or if you manually deleted /system/app files without proper knowledge, a factory reset won’t help. Raw firmware rewrites the entire system partition, erasing all modifications.
Unlike sideloading a custom ROM, raw firmware requires a connection between a PC and the phone while the phone is in a low-level state.
Many users seeking raw firmware are actually trying to install a custom ROM (LineageOS, Pixel Experience). Raw firmware serves as the base. If you want to install a custom ROM on the ZS620KL: asus zenfone 5z -zs620kl raw firmware-
Skipping the raw firmware step causes "assert failed" errors in TWRP because the ROM checks your firmware version.
Extract the raw firmware archive. You’ll see files such as boot.img, system.img, vendor.img, radio.img, recovery.img. If you installed a malicious APK that wrote
Connect the phone in fastboot mode (Power + Volume Up).
Flash partitions (example for 7.1.0‑raw): Unlike sideloading a custom ROM, raw firmware requires
fastboot flash boot boot.img
fastboot flash system system.img
fastboot flash vendor vendor.img
fastboot flash radio radio.img
fastboot flash recovery recovery.img
fastboot reboot
Verify the device boots into stock Android 8.1.
Tip: If you encounter “verification failed” on
radio.img, use thefastboot flash radio radio.img --skip-verifyflag, then re‑lock the bootloader if desired.