Dell E5440 completely dead, no LED.

[Andreasbest]

Hello!
I have a E5440 (second hand) that doesn't power on, it's not shortcircuited as the charger's led remains on when i plug it but i have low voltage.
Here are some measurements i took before and it's as far i can go with my knowledge so any help will be great.
PL301 17v in both pins instead of 19v
PU301 0v in pin5
Thank you in advance!

[piernov]

Re: Dell E5440 completely dead, no LED.

PL301 pin 2 is connected directly to PU301 pin 5 so those measurements are probably wrong.
First thing is to tell the history of the machine, if it's liquid damaged, give all the symptoms, visual inspection, etc…

[Andreasbest]

Re: Dell E5440 completely dead, no LED.

Yes this is what i thought too but i really don't found connection betwen them even with the ohmeter.
I count 5 pins from the dot counter clockwise.
No liquid damage, motherboard looks like new, no LED at all, no battery charging, not any other symptoms of life.

[piernov]

Re: Dell E5440 completely dead, no LED.

Did you try another Dell AC Adapter (with correct power rating)?
If yes, you can start measuring voltage on inputs/outputs of the 3V/5V regulator PU51.
Pin 3 VREG3
Pin 6 EN2
Pin 8 SW2
Pin 12 VIN
Pin 13 VREG5
Pin 18 SW1
Pin 20 EN1

[Andreasbest]

Re: Dell E5440 completely dead, no LED.

pin 3 0v
pin 6 0v
pin 8 0,24v
pin 12 17,24v
pin 13 0v
pin 18 0,03v
pin 20 0v

What do you think?

[piernov]

Re: Dell E5440 completely dead, no LED.

PU51 does get 17V on its power input pin VIN but never creates the LDO outputs VREG3 and VREG5.
Chip is TPS51225C according to schematics, for which VREG3 and VREG5 should always be enabled.

Confirm that the chip on the board is indeed TPS51225C
Measure resistance to ground on PU51 pins:
Pin 3 VREG3
Pin 8 SW2
Pin 13 VREG5
Pin 18 SW1

[Andreasbest]

Re: Dell E5440 completely dead, no LED.

Yes it's indeed TPS51225C (1225C is written on it)
Pin 13 is grounded.

[piernov]

Re: Dell E5440 completely dead, no LED.

What's the exact resistance to ground?
If you have a short to ground there you'll have to find it. You need to inject 1V on this pin with a lab PSU and check what the current consumption is, then search for the component that's heating up.

[Andreasbest]

Re: Dell E5440 completely dead, no LED.

0,5Ω is the resistance to ground.
So it's not the PU51 that is faulty but another component that i must found using vontage injection?

[piernov]

Re: Dell E5440 completely dead, no LED.

Just realized that apparently there's only PU51 and PC69 on the +5V_ALW2 line. Weird, but I guess it makes things easy.
Remove PC69 first, then if the short to ground is still there remove PU51, and confirm the short to ground is gone.

[Andreasbest]

Re: Dell E5440 completely dead, no LED.

.

[Andreasbest]

Re: Dell E5440 completely dead, no LED.

Ok found it, was right after the pin 13, i removed it, the pc69 is not shortcircuited but the pin 13 remains shortcircuited to ground.
So the PU51 is faulty or i need to remove it and check for shortcircuit again?

[mcplslg123]

Re: Dell E5440 completely dead, no LED.

Yes, should remove PU51 and check resistance on pin13 again.

[Andreasbest]

Re: Dell E5440 completely dead, no LED.

@ piernov & @mcplslg123
Just removed the PU51 and the shortcircuit is gone.
So it's PU51 broken?

(sorry for the delay was on vacation for New year eve)

[mcplslg123]

Re: Dell E5440 completely dead, no LED.

@ piernov & @mcplslg123
Just removed the PU51 and the shortcircuit is gone.
So it's PU51 broken?

(sorry for the delay was on vacation for New year eve)

Yes, seems like that. Replace the chip and dont put power to mb without this chip.