Dell E6430 shortcircuit

[Andreasbest]

Re: Dell E6430 shortcircuit

Don't remove Jumpers blindly. By the looks of it, you have a short on 19V rails (system side) [Assuming you removed PQ914 and pin 5 to 8 is not shorted to ground].

The shorted rail is named +PWR_SRC. Jumpers are usually present when another 'section' of the board need 19V to convert it to something else, as is the case with PJP702 where the 19V will be converted to +VCC_GFXCORE.

Removing jumpers to find shorts is only really helpful to figure out which 'section' is faulty/shorted but is useless if the fault is on +PWR_SRC.

Think of it like this:
Imagine you have an underground main water pipe that feeds say 5 houses. Each house gets water from the main pipe through a vane/valve (which in your case is the jumper).

Now say you get a complaint that water is leaking. You could eliminate leaks through the houses by closing the water vane/valve for each house.

But there is also the other possibility that the leak is coming from the main pipe itself in which case closing the valve/vane would not be helpful since the leak could be anywhere along said pipe. In such cases you might maybe inject a marker in the water and use a detector to locate the leak (which in your case is analogous to injecting voltage and feel for what gets hot).

Hope that somewhat helps.

Coming back on topic, if you cannot find anything wrong visually I suggest you inject voltage and locate what gets hot.

Yes I understand.
I opened the jumpers just to exclude areas from searching and losing time.

[Spider1211]

Re: Dell E6430 shortcircuit

What is the resistance to ground on the 19V rail by the way?

[Andreasbest]

Re: Dell E6430 shortcircuit

What is the resistance to ground on the 19V rail by the way?

i measure resistance between PQ914 1 2 and 3 (same pin, just mentioned them all) and ground, is 3.5Ω

[Spider1211]

Re: Dell E6430 shortcircuit

Hmmmm, it could also be a high side mosfet that failed. Check continuity across PQ700 (PQ701 should be empty, but test across it too if present).

[Andreasbest]

Re: Dell E6430 shortcircuit

PQ700 upper pins are all grounded, bottom no.
Same on missing PQ701.

[Spider1211]

Re: Dell E6430 shortcircuit

which are upper & lower pins? Is the CPU removed or present? Measure continuity across PQ704 and PQ705(if present)

[Andreasbest]

Re: Dell E6430 shortcircuit

Upper pins are those with the dot on their side (the dot is in middle top)
PQ701 (Not present) PQ700, PQ704 and PQ705 have common upper side (all with dot up middle) so the upper side on all of these is grounded.

[Spider1211]

Re: Dell E6430 shortcircuit

Did you measure continuity across the mosfets mentioned above? Is the CPU installed when you are measuring?

3.5ohm is not a direct short to ground, its likely that the main rail is grounded through maybe the CPU or GPU (if present) via a shorted high side mosfet. Hence why we are measuring the above.

[Andreasbest]

Re: Dell E6430 shortcircuit

Yes i measured continiuity to ground of the mosfet you mentions, the one side of them is common and are all shortcirctuit to ground
In Ω i get 0.05 (the same like when i short the probes together)
The same on PQ914 1 2 and 3 pins, forget the 3.5Ω ,probably something went wrong with my multimeter in that measurement.
CPU removed, No GPU in this mb.

[Spider1211]

Re: Dell E6430 shortcircuit

Ah ok. If Main rail to ground is 0.05ohm then its a dead short, injecting voltage should help a lot here since you cannot visually find the fault. Do you have a bench supply to do so?

[Andreasbest]

Re: Dell E6430 shortcircuit

Yes i do. I'll start with 19v 1A and check the area i isolate with the open jumpers.
If i only had that thermal camera

[Spider1211]

Re: Dell E6430 shortcircuit

Yes i do. I'll start with 19v 1A

NOOOOOO!!!! Start with 1V 1A then increase the amp only. If nothing gets hot, increase the voltage slightly.

Always start at lowest voltage setting to make sure you do not fry CPU, GPU, chipset, etc if ever a high side mosfet is shorted.

If i only had that thermal camera

Lol, don't we all. Use the "Finger licking good" technique instead

[Andreasbest]

Re: Dell E6430 shortcircuit

i usually start with 19v and 0.5A. Ok i'll do it your way.

[Spider1211]

Re: Dell E6430 shortcircuit

You can if you are absolutely certain it wont go to the voltage sensitive parts. Or if you don't mind possibly frying a CPU, chipset, etc.

This is specially an issue with newer driver chips where the mosfets and driver chip are integrated in a single chip. I recently had atleast 2 laptops with exactly that, high side mosfet for soc was shorted.

[Andreasbest]

Re: Dell E6430 shortcircuit

Ok i'll do it your way and come back with results )

[Spider1211]

Re: Dell E6430 shortcircuit

All the best!

[Andreasbest]

Re: Dell E6430 shortcircuit

PQ5 gets extremely hot at only 19v @0.5A

Replaced it but the shortcircuit is still there, removed it and the PQ914 1 2 and 3 pins shortcircuit is still there.
??

[Spider1211]

Re: Dell E6430 shortcircuit

Inject voltage on pin 123 of pq914. Again, start at 1V 1A then increase slowly and see what gets hot.

[Andreasbest]

Re: Dell E6430 shortcircuit

Ok found the guilty
Was a shorted smd cap in bottom of the mb.
Now i face another problem though and i'm worry about the chipset.
When i apply power the power on button and the caps lock led flget immediately light up, nothing display on screen, fan not spinning and after some seconds powers off and power on again in same state.
I'll try bios dump, i hope i didn't damage the chipset somehow.

[Spider1211]

Re: Dell E6430 shortcircuit

Dell is a bit weird. Remove the CMOS battery, plug in the charger wait 1 second, remove the charger then quickly plug it in again. It should cycle 2-3 times then turn on.

Is the speaker connected? If not, connect it before turning ON. Report back if it beeps when you turn on and how many beeps.