Lenovo ThinkPad T480 does not start

[Markus1741]

https://www.badcaps.net/forum/troubl...9-2v-thank-you

I was asked to start my own thread and would now continue working from the thread here.

Remove all power. Meter in resistance mode. Measure the resistance (not DIODE mode) to ground of VSYS_OUT. This is the main power rail that powers the logic board. Checking if this main power rail is shorted which will be sensed by the charger IC and cause the DCin path mosfets to turn OFF.

If this resistance is not low, proceed...

Review the next stage of this circuit @ dual mosfet PQ101. What voltage to ground do you see on PL101 ? This leg of the circuit is driven by the charger IC @ PU101.

If there is a low or no voltage on PL101, then proceed to investigate the PU101 IC.

(Carefully) Measure the voltage to ground of:

VBUS ; pin 1
REGN ; pin 28


Post each measurement.

Coil PL101 Volt to ground 0,298V

VBUS ; pin 1 = 20 Volt
REGN ; pin 28 = 6 Volt

[fredyjbi]

https://www.badcaps.net/forum/troubl...9-2v-thank-you

I was asked to start my own thread and would now continue working from the thread here.

Remove all power. Meter in resistance mode. Measure the resistance (not DIODE mode) to ground of VSYS_OUT. This is the main power rail that powers the logic board. Checking if this main power rail is shorted which will be sensed by the charger IC and cause the DCin path mosfets to turn OFF.

If this resistance is not low, proceed...

Review the next stage of this circuit @ dual mosfet PQ101. What voltage to ground do you see on PL101 ? This leg of the circuit is driven by the charger IC @ PU101.

If there is a low or no voltage on PL101, then proceed to investigate the PU101 IC.

(Carefully) Measure the voltage to ground of:

VBUS ; pin 1
REGN ; pin 28


Post each measurement.

Coil PL101 Volt to ground 0,298V

VBUS ; pin 1 = 20 Volt
REGN ; pin 28 = 6 Volt

multi resistor mode what is the resistance value of VSYS_OUT if it is not short to ground normally it must be OL or must be high Mohms, PQ1 pin 5678 must be 20v, PQ3 pin 2 TBT_HV_GATE must be 3.3v, PQ4 pin 2 VCC3_LDO_TBT must be 3.3v