Dell Latitude 5520 motherboard (SouthPeak15 TGL MB 8L model)

[rafaa_2000]

Hello,
I am working on a Dell Latitude 5520 motherboard (SouthPeak15 TGL MB 8L model). When I plug in the charger and take measurements at the MOSFETs (Q7408 and Q7421), I get a voltage of 5V.


I have measured all the voltages as well as the resistances of the coils, which you can see in the attached photo.


After removing the MPNR 2941B147 (PU5001) component, the voltage at the MOSFETs (Q7408 and Q7421) increased to 20V. I also took new voltage measurements, and the results are available in the photo.


Additionally, when I connect only the battery (without the charger) and press the power button, the light comes on for a while and then turns off (this happens without the PU5001).
Could anyone help me diagnose this issue?
Thank you in advance!

[reformatt]

Power sequence is on pg 102 of the 19819-1 schematic - you start there. What reasoning did you have to remove PU5001? I would expect at least 1D8V_S5 on PL5301 which is prior to that in the sequence.

20V from USB-C is not overly important when troubleshooting as this machine uses a NVDC charger and it will boost up main power rail to roughly that of the nominal battery voltage when only fed 5V.

[rafaa_2000]

Thank you for your response. The voltage measurement at point PL5301 shows 1.7V. According to the power sequence outlined on page 102, the next step would likely be to check the PCH_DPWROK signal at resistor R1745, if I am not mistaken.

[reformatt]

There are letters and numbers on the power sequence. Letter sequence is the state of the machine prior to power button press, and number sequence is after.

1D8V_S5 is i in the sequence, next is 1D8V_VCCIN_AUX is j. Power good signal from TPS51396RJER drives the enable for MP2941BGL (which you removed). This in turn drives APW8743CQBI (k). So the sequence stops at this point because of the missing voltage from your removed chip.