ThinkPad T490s only starts with battery

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  • rumpumpel1
    Senior Member
    • Jul 2019
    • 140
    • germany

    #1

    ThinkPad T490s only starts with battery

    I am testing a ThinkPad T490s with this setup: only the bare mainboard NM-B891 with a fan and the small Power-On daughterboard as well as with a USB-C monitor (no BIOS battery!).

    If I connect a battery, the mainboard starts up normally. After about 50 seconds the logo appears and after another 30 seconds the final message “... System configuration is invalid. Press Esc to continue or F1 to enter setup”.
    If I connect the power supply unit instead of the battery, a USB meter shows the usual fluctuating power consumption for approx. 30 seconds, then the mainboard switches off (power LED goes out). The USB-C monitor shows no image.

    If I connect the battery and power adapter, the Lenovo logo flashes briefly on the monitor after a while, but the final message does not appear as in the case of the battery. The USB meter only shows a few mA the whole time, so the battery is not being charged either.

    What could be the reason for this?


    schematisc and boardview can be found here:
  • mon2
    Badcaps Legend
    • Dec 2019
    • 14046
    • Canada

    #2
    What is the voltage showing on your USB-C meter? Is it 20V or stuck @ 5V?

    20V is required for a normal boot cycle. 5V is the power on default by the power delivery (PD) adapter.

    Comment

    • rumpumpel1
      Senior Member
      • Jul 2019
      • 140
      • germany

      #3
      The voltage is 20V.

      Comment

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