Lenovo Flex 5 15IIL05 not turning on

[mferna14]

Dear precious friends., I am working on a Lenovo Flex 5 15IIL05 (Motherboard LC55-15C 19792-1 448.0K105.0011). The problem with it, does not turn on at all. I see the battery charging LED but no response from the power button. Output coils 3.3V & 5v are perfect. LDO 3V is also present, I measured this on the power button. The on/off button is working perfectly. I re-programmed with new bin files & the status is still the same. I do not see any abnormal voltage & any Shorts or any kind of liquid spill. The MB is clean. I am using this schematics Lenovo Flex 5-14IIL05 19792-1, seems to be the same. Can anyone help me in with this repairs thanks in advance.

[mon2]

Test the voltage to ground of ALL_SYS_PWRGD.

[mferna14]

Thank mon2., absolute ZERO volts....I check on U1701 pin # 5, the board is missing the 3D3V_SUS rail... Pls. guide me what to do next. Thanks dear

[mon2]

Check the EC power rails. Out of the office so do not have access to the schematic database. My schematic has the power on sequence. See if you have the same near the end of the pdf.

[mferna14]

mon2., Want to verify that this model Lenovo motherboard takes PWR_DCBATOUT as 13.18V & throughout the motherboard on this rail???? The INPUT to the first MOSFET PU4403 is 19v... But once the voltage is out from this MOSEFT, there is voltage drops to 13.18V & on this inductor PL4401 it even drops to 10.90v. The output of the 2nd MOSFET PU4405 is 13.18V ... Similar to the Dell & Hp newer motherboard I guess!!! The 3.3V & 5V comes on fine in the start & stays for a whiile, then fluctuates, & no voltage on these 2 output inductors. 3D3V_S0 is not present at all. Thanks dear

[mon2]

See attached. Do you have the preceding voltages @ step 6? Step 5?