Help me repair this UX305 motherboard please

[Clinteastwood1]

Re: Help me repair this UX305 motherboard please

Ok some people told me it's not reliable to use the ohmmeter to test mosfets so I took all the measures again in diode mode (testing random pins of the mosfets side by side). Please look at the pic below.
Red circles = faulty mosfets
Green circles=good mosfets
Yellow area = slightly hotter than the rest of the board

I really hope you can help me because I really do need this laptop

[Clinteastwood1]

Re: Help me repair this UX305 motherboard please

Little mistake sorry, pin 8 of winbond bios chip is not the right one, it's the first one at the top and it reads 1v (it's pin 5 that shows 0.28v).
It should read 3.3v I think so there is problem. Is this chip dead?

[mon2]

Re: Help me repair this UX305 motherboard please

On the flash chip, you are showing the voltage on pin #1 (pin close to the circle in the plastic housing). Then the pins count up going counter-clockwise.

So you have measured, pin 1 and pin 5 from the last diagram.

What is the voltage on pin 8 of this flash chip? It should be 3.3volts.

Also good to check and post the voltages on each grey coil. Each coil is linked to a voltage rail.

In general, each rail should work to make this laptop operate normally.

[Clinteastwood1]

Re: Help me repair this UX305 motherboard please

Hi Mon2 thanks for your help. I took some measures as per your suggestions. This time I took measures for all the bios chip pins to avoid confusion. Also for coils.
This area around the coils becomes very hot after a short moment.
Thanks I hope it helps

[Clinteastwood1]

Is this mosfet dead? Strange behavior

Hi,

I am trying to troubleshoot a laptop's motherboard, I measured the resistance of the 2 entry mosfets, and the second one seems to have a weird behavior.
As a matter of fact, it has an infinite resistance (meaning it's dead, right?) but when I measure its voltage it shows 19v as the first one, as if it was fine...
So is it dead or my method to detect dead mosfets is crap? ( I tried with the diode mode of my multimeter, it also shows there is a discontinuity)
Thanks for your help guys.

[SMDFlea]

Re: Is this mosfet dead? Strange behavior

Hi,

I am trying to troubleshoot a laptop's motherboard, I measured the resistance of the 2 entry mosfets, and the second one seems to have a weird behavior.
As a matter of fact, it has an infinite resistance (meaning it's dead, right?) but when I measure its voltage it shows 19v as the first one, as if it was fine...
So is it dead or my method to detect dead mosfets is crap? ( I tried with the diode mode of my multimeter, it also shows there is a discontinuity)
Thanks for your help guys.

Your thread post has been moved from the "Troubleshooting Desktop Motherboards, Graphics Cards, and PC Peripherals" forum to this thread.

[SMDFlea]

Re: Help me repair this UX305 motherboard please

The best way to test mosfets is to desolder them and test on the bench. What make/model is your meter ?

.

[Clinteastwood1]

Re: Is this mosfet dead? Strange behavior

Your thread post has been moved from the "Troubleshooting Desktop Motherboards, Graphics Cards, and PC Peripherals" forum to this thread.

This thread was confusing enough with all my measures and posts I don't think it was a good move adding the mosfet measuring question, this thread is already overloaded I think and nobody still participate to it...
Ok thanks for your reply mate, if I desolder it I will replace it straight away no need to test it
I am going to replace all the mosfets on my board i guess, because I'm afraid I won't be able to troubleshoot it
Cheers

[SMDFlea]

Re: Help me repair this UX305 motherboard please

Ah so you can desolder them. OK go ahead,desolder them and test them first before buying new ones. Maybe this will help - http://mayohardware.blogspot.com/201...g-mosfets.html

[Clinteastwood1]

Re: Help me repair this UX305 motherboard please

Thank you very much for the link SMDFlea I'm sure it will help me avoid desoldering mosfets for nothing. I hope I will be able to find my motherboard's problem too, thanks again

Edit: thanks to your link I realized the diode mode has to be used taking into account the sense of the measure. So I took new measures and my mosfets are all fine.

Now with this new information i hope someone here can help diagnose the board.
Here are my last mesures in the 3v/5v area (hot zone)

[Techtiger]

Re: Help me repair this UX305 motherboard please

Assuming you don't have a power Lab to find the short there is a alternative method give a try (FINDING SHORT ON MOTHERBOARDS WITH COMPRESSED AIR https://www.youtube.com/watch?v=AOALg_rDIZk )

put the multimeter continuity test the 2 coils on red and musure the readings the yellow is you 3/5 Regulate do the COMPRESSED AIR test arround this chip and see

[Clinteastwood1]

Re: Help me repair this UX305 motherboard please

Mate this tut is magic thank you !!!
I don't have any compressed air right now but seen in the comments that you could achieve the same with gas lighter oil or isopropyl alcohol, since I have both I'm gonna test it this way.
Before doing it (I'm not at home right now) and since this area on my board is very hot, couldnt we just conclude it's the chip you circled in yellow which is faulty, since coils don't get faulty, right?

And 2nd question, this chips reads "1285a tp 5c8 a3sh" do you know if I can replace it with this one with a slightly different ref since I can't find the exact one:

https://www.ebay.fr/itm/1PCS-TPS5128...b-15db0b89a2f9

Thanks again for this cool idea, and if this chip is making my MB faulty I surely owe you a big one my friend !

[Clinteastwood1]

Re: Help me repair this UX305 motherboard please

I made the alcohol test and the only chip on which alcohol evaporates very fast is this 3/5v regulator. I tested all the chips on the board and coils and mosfets and other components this is the only one causing the alcohol to evaporate in a heart beat.
Is there something else could test? Or I can replace this chip and hope for the best...
These chips are very tiny compared to the others, it won't be easy I should probably buy a dozen of them just in case

[SMDFlea]

Re: Help me repair this UX305 motherboard please

Have you desoldered/soldered a QFN chip before ? ,do you have a hot air station

[Clinteastwood1]

Re: Help me repair this UX305 motherboard please

I've watched videos on YouTube haha.
I'm gonna buy an air gun, I already have a microscope, a soldering iron, and flux, so it should be fine. I will train myself on another old motherbord first.

[SMDFlea]

Re: Help me repair this UX305 motherboard please

I've watched videos on YouTube haha.
I'm gonna buy an air gun, I already have a microscope, a soldering iron, and flux, so it should be fine. I will train myself on another old motherbord first.

What type of air gun, not the paint stripper type i hope

[Clinteastwood1]

Re: Help me repair this UX305 motherboard please

Not the elon musk's one at least
If you have one to advice me please let me know, or I'll buy one from Amazon considering the reviews. Not to expensive though since it will be for a one time use.
This guy on yt even replace this kind of chip without any air gun, only zooming with his phone
https://youtu.be/ljyGMOi5JPo


My chip ref is something like "1285a tp 5c8 a3sh", I found similar chips but the end of the ref isn't exactly the same, I guess my chip is a "TPS51285A" as well so it should be fine ?

https://www.ebay.fr/itm/1PCS-TPS5128...0/152822560965

https://www.aliexpress.com/item/32813670403.html

[Clinteastwood1]

Re: Help me repair this UX305 motherboard please

I bought it from ali I suppose they are the same.

[SMDFlea]

Re: Help me repair this UX305 motherboard please

The guy on youtube hasn`t desoldered a QFN chip,he`s only soldering one around the edges, he hasn`t soldered the centre pad. https://www.youtube.com/watch?v=c_Qt5CtUlqY
The 858D is about as cheap as you`ll get for a hot air station, i`m not recommending it though,as they have some well known quality control and build problems, but you can check the prices and YT videos .As its only a one-off you could take the part and board to a phone/pc repair shop ,they should be able to solder it cheaper than the cost of a hot air station.

[Stevedb]

Re: Help me repair this UX305 motherboard please

It is possible that the output from the chip is shorted I would first check the VIn , EN1 , EN2 , LD03.3, LDO5 pins are shorted. Which ic do you have on your board.

Good luck

Best regards

Steve