Just found this on h-node:"Append acpi_backlight=vendor to GRUB_CMDLINE_LINUX_DEFAULT. Then run sudo update-grub."
Basically, try adding "acpi_backlight=vendor" to the GRUB_CMDLINE_LINUX_DEFAULT this time. This advice was found on Aspire V5-471's entry details. This model has been commercialized in 2012 according to h-node.
