Dell Latitude 3390 short on power adapter.

[Andreasbest]

Hello.
I bought a faulty 3390 for my self, it has shortcircuit upon inserting the power supply and the led of it goes off immediately.
I found a blown mosfet PU4301 that i replaced, after than with the use of a thermal camera i found a nearby capacitor PC4306 to be "burning", replace it too but the short is still there and the new capacitor is burning too.
What am i missing?
Boardview and Schematics https://www.badcaps.net/forum/troubl...-cad-boardview

Thank you!

[Sephir0th]

You likely forgot to check the health of the main power rail before starting with your work at this capacitor. At PR4402 for example.

[Andreasbest]

You likely forgot to check the health of the main power rail before starting with your work at this capacitor. At PR4402 for example.

Thank you for replying and yes that's true, after desoldering of PR4402 i got short on top pin to GND.
What do you suggest next? Power injection 1v 1a?

[Sephir0th]

Yes, start with 1A and raise the current in 1A steps if necessary. Don't raise the voltage as long as it is not clear whether it is a short to GND or a short to a high-current buck converter (CPU/GPU). The clue about this question usually comes from the exact resistance compared with the resistances of aforementioned buck converters.

[Andreasbest]

I tried with 1v 1a but nothing got hot, then i raised V until 3v but never managed go more than 0.7v, so i raised A to 3, this raised correctly so i inject a total of ~3w but still nothing got warm.
I was affraid to go more than that, i don't want to burn the copper trace.
What do you suggest next?

[Sephir0th]

Share the exact resistance to GND please. If it ia a capacitor, it should warn up. Iirc correct I have advised to not move with the voltage above 1 Volts, since it can be the case that the voltage feed more or less directly the CPU or GPU.

[Andreasbest]

I'm away from the bench for the next 2 days, i'll check the resistance Monday morning and i'll share the measurement.

Yes, i rarely go over 1v too, thankfully it was impossible to go over 0.7v thanks too the short )

[Andreasbest]

The exact resistance of upper PR4402 to GND is 0.8Ω, practically 0.
What do you suggest next?

[Andreasbest]

Someone? Anyone???

[Andreasbest]

Bump

[Andreasbest]

Bump

[Andreasbest]

Bump

[SMDFlea]

Bump

Post a link to the schematic/boardview

[Sephir0th]

The exact resistance of upper PR4402 to GND is 0.8Ω, practically 0.
What do you suggest next?

Is there any inductor present on the mainboard which reads the same 0.8 Ohms or similar resistance to GND?

[Andreasbest]

Is there any inductor present on the mainboard which reads the same 0.8 Ohms or similar resistance to GND?

I measured all coils (if this what you mean by inductor) but no, no 0.8Ω anywhere.

[Sephir0th]

Then, In theory, there is no reason against to raise the voltage in small steps. The short-circuit is strong, so normally you should find a capacitor at some point. Better advice would be of course to observe the board with thermal camera while injecting 1Volts.

[Andreasbest]

Then, In theory, there is no reason against to raise the voltage in small steps. The short-circuit is strong, so normally you should find a capacitor at some point. Better advice would be of course to observe the board with thermal camera while injecting 1Volts.

Yes this is what i do, with thermal camera i go up until 1v 3a but no heat at all, both sides.

[Andreasbest]

Bump

[Andreasbest]

Bump

[Sephir0th]

Alright, then, we likely need to collect more informations. Share what current the short-circuit takes with 1V, to start with.