Vestel TVs are picky. Follow these rules strictly:
Now, take the prepared USB drive to your TV and follow this sequence: vestel firmware update usb
Failure to properly format the USB drive is one of the most common reasons the update fails to start. Vestel TVs are picky
Some Android-based models (e.g., 17MB170 running Android TV) require a different button combination or bootloader menu access. Try holding and POWER instead of OK. If you cannot access recovery, professional service may be required. vestel firmware update usb
Vestel devices use two different firmware update approaches. The is for dead or bricked devices, while the core update is for minor improvements on a functioning TV.
Model: 55UHD5500 Chassis: 17MB120S