Replacement mosfet

[Tony.T]

Have a dell computer that is broken.  Before the two first mosfet pairs of the 19v powerrail i found this mosfet that was making some weird sound.

mosfet 6428 gv7c36

But can not find this chip anywhere on the internet. Anyone that can give med som help of a replacement chip?

As it is the only mosfet (not a pair) in the beginning directly after the powerinput...i did not dare to shorten the drain and Source.  .. or is it ok?

cheers...

[fzabkar]

Is your Dell listed here?
https://elektrotanya.com/showresult?what=dell&kategoria=notebook-pc&kat2=schematics

Can you tell which numbers could be date/batch codes? This can sometimes be discerned from other ICs on the same PCB.

Could we see a photo of the part and the surrounding circuitry? Designers often stick with one IC manufacturer, so identifying the other ICs may help to identify your MOSFET.

[shakalnokturn]

Original should be AON6428 not sure why that should make noise tough, more like a nearby inductor.
Anyway you can find fakes of this one on ebay, originals on DigiKey.

STL58N3LLH5 is one suitable replacement, I'm sure there are others, try parametric searches on Mouser, Farnell, Radiospares, Digikey...

[Tony.T]

Here you can se the location of the mosfet.  6428, GV7C36, Just wonder if one could just short the dran and source to get it work. As it seems that the 19V rail stops here. But little afraid that it could damage some other things that might need less voltage?

[Tony.T]

Here is the other side.  i was hoping that these two mosfets was the absolut first ones...then one could just remove one of the mosfets and shorten the drain and source....but as the removed one was alone...it conduses me.

but the small one bottom right hand has 19.5V. ??!!

[Tony.T]

Dell latitude 5570. 

[wraper]

MOSFETs do not make any sounds period. It's either ceramic cap or inductor. However even if there is any sound it does not mean that part emitting it is faulty.

[Psi]

MOSFETs do not make any sounds period.

Sometimes they make a BANG sort of sound, often followed by one or even two ricochets.

[Tony.T]

Well...might be that the coil made the sound.  but the mosfet got very hot and both the motherboard as the powersupply made a very high sound when powered on.

Might be a short AFTER the mosfet ...but the question i have is rather...can i put 19.5V at the source of this mosfet...without doing a huge mistake  :-)..just to see if there is another thing shorted..

Even if the mosfet got really warm...it could be something after it...

[Tony.T]

hmmm...seems to be shorted after the mosfet.  When putting 19.5V on the coil after the mosfet it sparkles..  (0.5A, 19.5V).  Directly connected to earth.
Just thinking of increasing the amperes to see what get hot....
anyone that can confirm that im going the right way??!!

[wraper]

hmmm...seems to be shorted after the mosfet.  When putting 19.5V on the coil after the mosfet it sparkles..  (0.5A, 19.5V).  Directly connected to earth.
Just thinking of increasing the amperes to see what get hot....
anyone that can confirm that im going the right way??!!

You should not use high voltage for finding short because you can destroy CPU/GPU if high side mosfet is shorted in VRM.

[Tony.T]

that i understand.  because it takes 1.3 volt right.  But thinking that on the 19.5V powerrail that early after the powerinput should not be any problem. ??  The mosfets near the processor is the one giving the voltage to the CPU/GPU

[wraper]

that i understand.  because it takes 1.3 volt right.  But thinking that on the 19.5V powerrail that early after the powerinput should not be any problem. ??  The mosfets near the processor is the one giving the voltage to the CPU/GPU

Do you understand that VRM high side mosfets are directly between 19.5 V and CPU? If it is shorted, you put 19.5 input voltage directly into CPU. The only thing that can save it is that PSU may not supply enough current, however bulk capacitance charged to 19.5V may be enough to kill it.

[Tony.T]

ahh,,,ok...i understand what you mean here. 

any idea how to find the short then? Method.  just desoldering piece to piece ?

[Tony.T]

found the shorted mosfet....
just beside the cpu.  Wonder if the cpu is fried.....

Removed it and no short to ground anymore.  No coil whining etc. 

[wraper]

Removed it and no short to ground anymore.  No coil whining etc.

Well, it's not short to ground but short to CPU which has very low resistance to GND. If CPU is fried or not depends on your luck.

[wraper]

BTW it's not just a mosfet. It's a whole power stage with 2 mosfets and gate driver built in. Also you could try testing it as is, with SiC530 removed. If CPU is alive it will likely run with remaining power stages.

[Tony.T]

OK...thanks mate.
There is another mosfet just beside the one that was fried.  Will try to run it without replacing the faulty one. Just another strange thing.  When i measure the voltage over the supposed 19V rail....it is only 14 now.   That seems to low.  But at the processor and ram memory it is 1.3V....  But i thought it should be 19V all over the motherboard before any mosfet.

Appreciate your help very  much....

[wraper]

OK...thanks mate.
There is another mosfet just beside the one that was fried.  Will try to run it without replacing the faulty one. Just another strange thing.  When i measure the voltage over the supposed 19V rail....it is only 14 now.   That seems to low.  But at the processor and ram memory it is 1.3V....  But i thought it should be 19V all over the motherboard before any mosfet.

Appreciate your help very  much....

It certainly shouldn't be 19.5V there. There is another step-down converter in between.

[Tony.T]

ok....i thought that it should be 19.5V around the whole motherboard before each mosfet that provides lower voltage to its nearest components.  one learns all the time.

Thank you for your explanations...and patience  ....

i have just put everything together and i have powerled now... :-)....keep fingers crossed.... :-)

[Tony.T]

Damn....

Fan goes on.  works for 5 seconds...turns off for a second...then on again for 6-7 seconds...then turns off.   Blinking one white flash followed by 2 orange flashes.  4-5 times.  Then same sequence again.

Hmm....

[Tony.T]

Damn...

CPU Fried.....

[wraper]

There is another mosfet just beside the one that was fried.

So you did not replace faulty power stage yet? As it's apparently only 2 phase, it's not a surprise it does not work with half of phases missing.

[Tony.T]

I have ordered a new mosfet. Will solder it on place as soon as i receive it.  The led sequence is telling me that it is a CPU failure.  But as you say...probably it needs all the phases.
I thought that you meant before..... that it will still work with only one phase...but my wrong.

Thank you for having patience with me.... :-).  i really appreciate your help.

will be back as soon as i receive the new SIC530...

[wraper]

I have ordered a new mosfet. Will solder it on place as soon as i receive it.  The led sequence is telling me that it is a CPU failure.  But as you say...probably it needs all the phases.
I thought that you meant before..... that it will still work with only one phase...but my wrong.

Thank you for having patience with me.... :-).  i really appreciate your help.

will be back as soon as i receive the new SIC530...

When like 1 out of 4 is missing, usually it will work. Depends on protections implemented as well. But cutting phases by half is too severe.