lenovo w540 mec1633 lkm-1 ws mb 12291

I welcome all good people in this forum :) I have a problem with repairing Lenovo motherboards. W540 LKM-1 WS MB 12291 I have 4 pieces of W540 motherboard - they all have the same symptom. - motherboard is switched on for a moment but the screen is black. - if the battery is inserted, the...