If the device no longer responds to any button or USB enumeration:

There is a profound existential danger in updating the TP.SK518D.PB802.

Unlike a smartphone, which has a failsafe "recovery mode" or can be force-restored via a computer, an LCD controller board is remarkably vulnerable. If the power flickers during the exact moment the flash memory is being overwritten; if the USB drive is formatted in the wrong file system (exFAT instead of FAT32); or if a technician accidentally flashes a firmware meant for the PB801 onto the PB802, the result is catastrophic.

The board becomes "bricked." It enters a state of permanent amnesia. It will not output a boot logo. It will not accept a signal. It becomes a piece of dead e-waste, salvageable only by desoldering the main chip and using specialized EEPROM programmers to manually inject the code via microscopic probes—a process that costs more in labor than the board itself.

Keep the previous version of the update (e.g., tp.sk518d.pb802_v2.1.0.bin) and its matching configuration backup. Rollback procedure: