Dell E5440 no ldo 3v5v,

[Tend0]

Hello everyone!
I have a Dell Latitude E5440 on bench that is completely dead, no led, no other activity like there is no power adapter connected.
The power_jack_in has voltage 19,5V, the PL4 has 19,5 in both sides and the PQ 4 has 19,5 Voltages and gate the pin 4 has 9,37v.
Main power rail +PWR_SRC_AC had 19,5v in PL400 but on +PWR_SRC i have only 0,50v on pl401
no ldo only 0,5v Come on VIN (12pin) TPS51125 PU51

+PWR_SRC and +DC1_PWR_SRC voltage IS 0,5v or it must be 19,5v what wrong?
Any advice?
Thank you advance!

schematic:

https://drive.google.com/open?id=1Qh...QwMB5GlHZQ2bN6

[mcplslg123]

Re: Dell E5440 no ldo 3v5v,

+PWR_SRC should be 13V approx on this platform. Check resistance on PQ400/404/406. Often PQ400 becomes leaky on this mb blocking the voltage on PL401. The resistance should be measured on 200K or higher.

[Tend0]

Re: Dell E5440 no ldo 3v5v,

PQ400 pin4 =60k, pin 1.2.3=216k, pin5=60k
PQ404 pin4 =190k, pin1.2.3=47k, pin5=250k
PQ406 pin4 =60k, pin 1.2.3=0k, pin5=250k
all mesure are took with black prob of multimeter to ground and red prob to each point on MOSFET
multimeter IS UT890c, resistor calibre:600k
thanks

[mcplslg123]

Re: Dell E5440 no ldo 3v5v,

Mosfet resistance is not checked this way.
need to measure it between mosfet pins like
01.Between Source(Pin 1-2-3) to Gate(Pin4)
02.Between Source to Drain(Pin 5-6-7-8)
03.Between Gate to Drain.

Measure resistance of listed mosfet this way and report back.

[Tend0]

Re: Dell E5440 no ldo 3v5v,

ok sir thanks
*PQ400: 01.Source(Pin 1-2-3) to Gate(Pin4) = 163k
02.Source to Drain(Pin 5-6-7-8) = 60k
03.Gate to Drain = 237k
*PQ404: 01.Source(Pin 1-2-3) to Gate(Pin4) = 83k
02.Source to Drain(Pin 5-6-7-8) = 329k
03.Gate to Drain = 406k
*PQ406: 01.Source(Pin 1-2-3) to Gate(Pin4) = 24k
02.Source to Drain(Pin 5-6-7-8) = 34k
03.Gate to Drain = 121k
thanks

[mon2]

Re: Dell E5440 no ldo 3v5v,

*PQ400: 01.Source(Pin 1-2-3) to Gate(Pin4) = 163k
02.Source to Drain(Pin 5-6-7-8) = 60k
03.Gate to Drain = 237k

Source - Drain resistance is too low.

Can you confirm the voltage to ground of the following on PQ400 ?

Source (1-2-3) ; select any pin
gate (4)
Drain (5-6-7-8) ; select any pin


Likely this mosfet is defective but best to check the voltages first and next remove this mosfet and check the resistance again when the part is OFF the logic board.

*PQ406: 01.Source(Pin 1-2-3) to Gate(Pin4) = 24k
02.Source to Drain(Pin 5-6-7-8) = 34k
03.Gate to Drain = 121k

Also the above readings are low.

[Tend0]

Re: Dell E5440 no ldo 3v5v,

the voltage to ground on
*PQ400

Source (1-2-3) =19v
gate (4)=19
Drain (5-6-7-8)=19,54


but in in
*PQ404 i have:
Source (1-2-3) =0,5v
gate (4)=1,03v
Drain (5-6-7-8)=19v
i think there is probleme


*PQ406
Source (1-2-3) =0v
gate (4)=0,47
Drain (5-6-7-8)=0,5

[mon2]

Re: Dell E5440 no ldo 3v5v,

*PQ400

Source (1-2-3) =19v
gate (4)=19
Drain (5-6-7-8)=19,54

See attached.

PQ400 = P-channel mosfet.

So this means that the GATE pin #4 must be a LOWER voltage than what it is passing between source / drain pins to ENABLE.

In your case, the voltage on the gate pin is the same as the source / drain pins which means this mosfet is leaking.

Remove this mosfet and replace with another - not super critical but share the part number of what you may consider as a replacement. It MUST be the same size, it MUST be a P-channel mosfet.

[Tend0]

Re: Dell E5440 no ldo 3v5v,

I removed it and replaced it by 74q3 mosfet
and voltage on gate IS 18v and the voltage on PL401 IS recover

[Tend0]

Re: Dell E5440 no ldo 3v5v,

thank everyone problème was solve After replace PQ400 the pl401 voltage recover and pc charge and turn on
best regard !!!
very happy

[mon2]

Re: Dell E5440 no ldo 3v5v,

Good work! Glad that you updated the thread for future readers.

The troubleshooting is from the above sticky by @Piernov on how charging circuits work.

https://www.badcaps.net/forum/showthread.php?t=90356

[Tend0]

Re: Dell E5440 no ldo 3v5v,

thanks so much
link will be very useful for me

[mcplslg123]

Re: Dell E5440 no ldo 3v5v,

thank everyone problème was solve After replace PQ400 the pl401 voltage recover and pc charge and turn on
best regard !!!
very happy

I knew it from the beginning. See my post#2

[Tend0]

Re: Dell E5440 no ldo 3v5v,

yes effectively I really appreciate your way of making me understand the process to find faulty componement in resistor mode I learned a lot and appreciate the way that the members are determinate for helping
you are best

[Tend0]

Re: Dell E5440 no ldo 3v5v,

Hello team, the PC that I replaced the pq401 came back with the same problem he told me that it happened overnight after diagnosis actually I find the same symptoms I have again I replaced the pqet nothing no voltage at pl401. i need your help for the rest thank you?

[mon2]

Re: Dell E5440 no ldo 3v5v,

Measure the voltage to ground of the mosfet at PQ400.

Meter in 30v or higher scale.

Red probe to source (1-2-3) pin.
Black probe to ground.

Repeat for gate (4). Repeat for drain (5-6-7-8).

What is the voltage of PU402,

pin #5 (ACOK) ?
Pin #20 (VCC) ?
Pin #16 (REGN) ?

Post each measurement.

[Tend0]

Re: Dell E5440 no ldo 3v5v,

DC IN = 19,96
PQ400 voltage: Source = 19,48v ; Drain = 19,96v; Gate = 11,50v
PU402 voltage :
pin #5 (ACOK) =00.00v
Pin #20 (VCC) =19,33v
Pin #16 (REGN)=5.99v

[mon2]

Re: Dell E5440 no ldo 3v5v,

pin #5 (ACOK) =00.00v

ACOK is NOT OK.

What is the voltage to ground of the ACDET pin ?

[Tend0]

Re: Dell E5440 no ldo 3v5v,

Acdet= 2,65

[mon2]

Re: Dell E5440 no ldo 3v5v,

ACDET is ok.

Confirm the presence of resistor @ PR425. Measure the voltage to ground on each pin of this resistor.

One side should be the same voltage as REGN pin = ~6 volts.

Then remove all power -> meter in resistance mode.

Check the resistance to ground of the ACOK pin. Based on the information posted, ACOK should not be @ 0 volts. This is an open-drain pin so the pull-up resistor @ PR425 is required.