Lenovo s145 fs441 fs540 no power

[Leo Emi]

Hi guys, I have a problem with this Lenovo laptop, I have no power at the first gate (red=power) (black=no power)
How can I troubleshoot this?

[Leo Emi]

schematic here:

Link to schematic - https://www.badcaps.net/forum/troubl..._fs540-nm-c121

[mon2]

Remove all power. Meter in resistance mode.

1) Measure the resistance to ground of PQ5302 - pins 5-6-7-8 (any of these pins is ok) to ground. Checking if there is a short on the main power rail which caused this event for the main power path mosfets to fail.

2) The main power rail mosfets are N-channel type so the gate voltage must be higher than the voltage being passed before source / drain pins to enable. Typically, gate voltage should be = adapter voltage + REGN voltage on the charger IC = 19v + 6v = ~25 volts.

3) With no power to the board, test the resistance across each mosfet in the power path:

source (1-2-3) & drain (5-6-7-8)
source (1-2-3) & gate (4)
gate (4) & drain (5-6-7-8)

Post each measurement. Each measurement must be hundreds of k ohms or higher or it may be defective.

Test the mosfet @ PQ5302 and also PQ5301. Do review the sticky above by piernov on charger circuits - a must read. Often, the 2nd DCin mosfet becomes defective.

4) With the power adapter connected, confirm the voltage to ground of REGN which should be ~ 6 volts.