Dell Latitude 5420 / GDF40 LA-K491P REV 3.0 / Amber / Orange light when power button is pressed

[zwect]

I have this Dell Latitude 5420 with ST: CMF62F3, board GDF40 LA-K491P REV 3.0 that does not power on, i already searched for some clues about this problem that happens on mine but no BIOS i downloaded and flashed did anything.
Only when the power brick is connected, when pressing the power button an amber light lights up at the front and slight decreases its brightness, the RAM and the CPU seem to heat up if the laptop is left connected but nothing else, other than USB devices getting powered.
Here is the original BIOS dump from the 25R256JVEN chip.

[zwect]

Update: Tested proper ME cleaned BIOS with the laptop's ST on it and no change in symptom.
PU102 heats up as soon as DC is connected to the laptop too. but i do not know if that should be normal on this model.

[mon2]

Remove all power. Meter in resistance mode. Measure the resistance to ground of the inductor @ PL101 (either side). Checking if there is a low resistance to ground on this power output rail = shorted part is present. Post the measurement in ohms. Suspects are the USB Vbus rails that consume the +5V.

[zwect]

Remove all power. Meter in resistance mode. Measure the resistance to ground of the inductor @ PL101 (either side). Checking if there is a low resistance to ground on this power output rail = shorted part is present. Post the measurement in ohms. Suspects are the USB Vbus rails that consume the +5V.

Measuring PL101 to GND gives 20.3Ohm

[mon2]

So there is a partial short on this rail. Everyone attached is a suspect. Would you have a thermal camera?

Review UI1 - pin 12. What is the resistance to ground here? If it is low, consider to flux and remove UI1 off the board and test again.

Check UI3 - USB load switch in sot23-5 package. Test the resistance to ground of pin # 1. USB load switches often short out with illegal USB loads. If the resistance is low here, flux and remove this part off the board and test again.

[zwect]

UI1's pin 12 gives some mega ohms that my multimeter cannot read and stays 0.L with a M at the top
UI3's pin 1 reads the same as UI1's pin 12
also no, i do not have a thermal camera, had checked PU102 with isopropyl alcohol method

[zwect]

Removing PJP103 seems to kill the short on PL101's side. PL101's resistance to ground goes up to 204 K Ohms.

[zwect]

Removing PJP103 seems to kill the short on PL101's side. PL101's resistance to ground goes up to 204 K Ohms.

+5V_ALW's resistance to GND now is 60Ohm after disabling PJP4 (and +5V_ALW_A_TBT reads 30Ohm), where to go from here?

[zwect]

Hello?

[zwect]

UPDATE: +20V_TBTA_VBUS_1 29Ohm
+20V_TBTB_VBUS_1 is 240K Ohm (not affected?)

EDIT: PD_VSYS at RT248's pin 2 (although not present) and UT3's pin 3 is 0Ohm is that how it should be?

[yesuha]

UPDATE: +20V_TBTA_VBUS_1 29Ohm
+20V_TBTB_VBUS_1 is 240K Ohm (not affected?)

EDIT: PD_VSYS at RT248's pin 2 (although not present) and UT3's pin 3 is 0Ohm is that how it should be?

did you managed to fix it? have same exact problem

[zwect]

did you managed to fix it? have same exact problem

Sadly not, and i didn't get any other clues

[mon2]

Your post #10 is a good clue. Review all parts on this low resistance to ground rail.

Start with fluxing and removing capacitor CT3. If the resistance to ground does not return to a much higher value, place this capacitor back onto the board.

Each part mated to ground on the 'EMI Part' red box are also suspects. It may also be true that the PD controller @ UT3 is 50% broken but doubt it for now.

I would flux and remove mosfet PQ1 off the board to essentially isolate parts of the board to hunt for the shorted part. Continue to review and post your updates here.

Most likely some USB Type C connector cross short during hot removal while the power adapter was @ 20V killed either the PD controller (partially shorting) or some other part on this network.

[yesuha]

did you managed to fix it? have same exact problem

Really Bad, i'll try removing UZ7 ,n ot getting hot but checked with 4 points method , it seems something around that área is shorted, Will try later and post results

[yesuha]

Sadly not, and i didn't get any other clues

some advances i made
at first got same symptoms led decresing etc...
found a short at +20V_TBTA_VBUS_1 removed ut3 got back to normal resistance to ground
found shorted +5V_ALW_A_TBT fixed by removing ut3 too
pjp4 is a joint only from +5V_ALW_A_TBT to +5V_ALW, as 5valw was shorted too (got some 14 ohms) removed PR607 it is like a bridge for PU601 - VIN_CPU_CORE , ohms at +5V_ALW side growth to 180, so i think PU601 maybe shorted too since at that side have 13 ohms only

have a question 180 ohms to ground at +5V_ALW is good? or should be higher in this motherbard?

edit: removed pu601 since it has some wires trough some resistors to 5valws short completely dissapeared, so at the end problem (i think) was pu601 and ut3, maybe generic charger fried the circuits, as i live at Mexico and don´t have access to UT3 will return to owner, forgot to tell removed UI3 usb power switch before too, was completely shorted
as i can see this mobo is fault prone, if you find anything as a partial short will need to find it trought different techniques, like overheating chips, good boardview analysis and kelvin probe method, gets easier as have a lot of "jumper" resistor and pads

[zwect]

some advances i made
at first got same symptoms led decresing etc...
found a short at +20V_TBTA_VBUS_1 removed ut3 got back to normal resistance to ground
found shorted +5V_ALW_A_TBT fixed by removing ut3 too
pjp4 is a joint only from +5V_ALW_A_TBT to +5V_ALW, as 5valw was shorted too (got some 14 ohms) removed PR607 it is like a bridge for PU601 - VIN_CPU_CORE , ohms at +5V_ALW side growth to 180, so i think PU601 maybe shorted too since at that side have 13 ohms only

have a question 180 ohms to ground at +5V_ALW is good? or should be higher in this motherbard?

edit: removed pu601 since it has some wires trough some resistors to 5valws short completely dissapeared, so at the end problem (i think) was pu601 and ut3, maybe generic charger fried the circuits, as i live at Mexico and don´t have access to UT3 will return to owner, forgot to tell removed UI3 usb power switch before too, was completely shorted
as i can see this mobo is fault prone, if you find anything as a partial short will need to find it trought different techniques, like overheating chips, good boardview analysis and kelvin probe method, gets easier as have a lot of "jumper" resistor and pads

just as i thought then, thank you very much nonetheless, i was afraid of desoldering UT3 and it not being the culprit since i do not have the tools yet to solder that kind of component back.

[zwect]

some advances i made
at first got same symptoms led decresing etc...
found a short at +20V_TBTA_VBUS_1 removed ut3 got back to normal resistance to ground
found shorted +5V_ALW_A_TBT fixed by removing ut3 too
pjp4 is a joint only from +5V_ALW_A_TBT to +5V_ALW, as 5valw was shorted too (got some 14 ohms) removed PR607 it is like a bridge for PU601 - VIN_CPU_CORE , ohms at +5V_ALW side growth to 180, so i think PU601 maybe shorted too since at that side have 13 ohms only

have a question 180 ohms to ground at +5V_ALW is good? or should be higher in this motherbard?

edit: removed pu601 since it has some wires trough some resistors to 5valws short completely dissapeared, so at the end problem (i think) was pu601 and ut3, maybe generic charger fried the circuits, as i live at Mexico and don´t have access to UT3 will return to owner, forgot to tell removed UI3 usb power switch before too, was completely shorted
as i can see this mobo is fault prone, if you find anything as a partial short will need to find it trought different techniques, like overheating chips, good boardview analysis and kelvin probe method, gets easier as have a lot of "jumper" resistor and pads

I removed PU601 and UT3 but i still have a short on +VCCIN at 20ohm and VSSIN_SENSE is 4.4ohm while PU601 is absent.
Should it be that low or are there more components affected?
Also my +5V_ALW can't be measured (stays M at my multimeter) so i guess that one is ok.