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We had a problem reported with the Lenovo Yoga 920-13IKB laptop (4k screen).
MemTest86 boots up OK, but at the start of running the tests the screen goes black. The memory testing continues with results written to the log file, but you can't see anything on the screen.
After investigation, we believe it is a UEFI firmware bug that Lenovo need to fix. Firmware version where the problem was seen is 5NCN29WW.
UEFI has two display modes. Console mode (which looks like the old style text only BIOS interface) and graphics mode. After switching from console mode -> graphics mode -> console mode, outputting text to the console no longer works.
MemTest86 boots up OK, but at the start of running the tests the screen goes black. The memory testing continues with results written to the log file, but you can't see anything on the screen.
After investigation, we believe it is a UEFI firmware bug that Lenovo need to fix. Firmware version where the problem was seen is 5NCN29WW.
UEFI has two display modes. Console mode (which looks like the old style text only BIOS interface) and graphics mode. After switching from console mode -> graphics mode -> console mode, outputting text to the console no longer works.