Problem Dell vegas/turis mlk kbl-r 17841-1 wx2rr

[Rofix]

Hi everyone, I wanted to kindly ask you for help, I have a problem with my Dell vegas/turis mlk kbl-r 17841-1 wx2rr PC, it turned off and I was no longer able to turn it back on, I'm checking the various voltages, unfortunately I found the 19 v up to the input components PU4411, PQ4401, thank you all for any advice

[mon2]

Review the POWER UP SEQUENCE DIAGRAM on page 102 of the schematics and post where the first rail stops.

[mcplslg123]

This board is notorious for RTC issues. First check whether cmos battery is 3.3V and then check RTCRST#/SRTCRST#.

[Rofix]

Good morning, I did some measurements and I'm posting various results the battery CMOS is 2,9 V

[Rofix]

Hi, I was trying to check for possible short circuits, on the 3.3 V part, I noticed something strange between the two MOSFETs at the output of PU 4504 and at the input of PU 4505. I have a very low resistance and I find myself with 3 Ohm, I tried even removing the mosfet to ground the PU 4505 but the result does not change

[mon2]

That is a good find.

If you suspect a defective mosfet, with no power to the logic board, measure the resistance across the mosfet pins:

source / drain
source / gate
gate / drain

To confirm, you have a low resistance to ground @ PL4502? Do not have power to the board during resistance / diode testing.

If yes, flux and carefully lift up one leg of PL4502. Then test the resistance to ground again. Which side of this now isolated power rail is with a low resistance?

Is it the producer side (PU4503) or the downstream / consumer side of this power rail? Is the resistance to ground still @ ~3 ohms?

Moving forward, would you have an adjustable power supply? If yes, dial it up to 1 volt (not higher) and 3-5A for injection onto the side with the low resistance. Check who heats up under this test method. You can use a thermal camera or IPA (alcohol) poured over the parts you suspect. Watch for the rapid evaporation of the IPA. Hope that it will be a capacitor.

[Rofix]

hi, I removed the PU 4504 and PU 4505 mosfets and checked them with a multimeter, they are ok, I lifted one leg of the PL 4502 coil, the resistance towards PU4504 and PU4505 is now 1.5 MegaOhm, I find the resistance of 3 Ohm on the opposite side towards the 3D3V_PWR

[mon2]

Moving forward, would you have an adjustable power supply? If yes, dial it up to 1 volt (not higher) and 3-5A for injection onto the side with the low resistance. Check who heats up under this test method. You can use a thermal camera or IPA (alcohol) poured over the parts you suspect. Watch for the rapid evaporation of the IPA. Hope that it will be a capacitor.

[Rofix]

I used a power supply with 1 volt and 2 amps to inject and unfortunately what heats up is not a capacitor, I think there's little that can be done here

[mon2]

[Rofix]

But how could this ever happen?

[reformatt]

Thought dead PCH y'day when I read this thread. Low ohms on 3.3V rail is usually that. Another CPU goes to silicon heaven.

As to why, it's usually some disruption on the 3.3V or 1.05V rail, due to liquid or insect damage, or something via a USB port (as most connect directly to the PCH). Or the PCH just flat out failed.

[Rofix]

Hi, thank you, at least I have an idea of what may have happened, even if unfortunately nothing can be done to fix it, thank you all for the advice,