Sony MHC-V90W Help Manual page 50

When you update using a USB flash drive, the update cannot be stopped. If the USB flash drive is removed or the home audio
system is unplugged during the update, the home audio system will malfunction.
Updating normally takes 3 to 10 minutes.
Do not operate the home audio system during an update. Also, keep the home audio system connected to the power supply and
network while updating.
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