Help me repair this MB please

Thread Starter

Clinteastwood1

Joined Apr 2, 2021
14
Hi,

I'd like to repair my laptop's motherboard UX305 i7 cpu). The laptop turned off abruptly when I was working on it and now it won't turn on again.
The charger is working fine (tested) and when I plug it nothing happens, no charging led, the laptop only vibrates slightly when I put my hand on it as usual meaning the current is passing through it. The laptop seems like dead though.

I tried:
- removing the battery and press the start button during one minute to drain out any current from the MB. No start up
- I tested the charger it's fine.
- I tested the charging connector it's fine.

The MB is faulty.

I've seen many videos and almost everytime the 2 mosfets which are near the charging connector and which play a safety role, are often the culprits

So I am planing to replace both. I don't know how to measure them to see if they are working or not (on the videos I've watched, it's not very clear to me) so nevermind I'll replace them straight away and hope I'll get lucky.

My question :
Could you please tell me if these 2 safety mosfets are the ones I circled in blue, or the ones in red? To be sure...
And can someone tell me the type/brand/model to buy as replacement.

Thank you very much for your help.
Best regards

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narkeleptk

Joined Mar 11, 2019
499
With power unplugged (cord and battery) use a DMM on continuity to find the first few components the power supply runs into. It may be those it may not be, too hard to tell from the picture. Once you find the first few components that the power supply runs into then check for shorts on the other side of them or hook up power and see if its making it past them. Keep going from one component to the next to see where your loosing power.If you have NO lights at all then your probably right and its the first mosfet the supply runs into.

Search "Electronics Repair School" on youtube. There is a guy named Sorin that does a lot of video's for laptops.
 

Thread Starter

Clinteastwood1

Joined Apr 2, 2021
14
Thank you much for your help narkeleptk.
Your troubleshooting method seems very smart, unfortunately I'm not skilled or knowledgeable enough to do this, when I look at the MB I can see so much components my head is spinning :)
Yes I'm 80% sure one of the 2 entry mosfets is down. According to many videos I've seen it's often the case when a laptop is faulty. I've probably watched the guy's channel you mentioned since I've watched plenty of videos.
Do you know where I can buy these 2 mosfets please, are they standard parts or I need to buy specific ones for my MB?
(I guess I'll replace the 2 in red on my pic above)
thanks again
 
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Thread Starter

Clinteastwood1

Joined Apr 2, 2021
14
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Thread Starter

Clinteastwood1

Joined Apr 2, 2021
14
That's a very good piece of news.

For the second mosfet too? Since mine reads "A5 GNA" and aliexpress one reads " A5 GND, A5 GNC, A5 PNB, A5"
I can't find A5 GNA online...
 

narkeleptk

Joined Mar 11, 2019
499
Not really sure about your dmm but usually diode mode you will see a 0 when bad. and a .5-.7 type reading when ok. Diode mode is not really how you test mosfets tho.

I do not repair pc's at all so my knowledge on them is very lacking but if it was in front of me and someone wanted me to check those mosfets I would plug in the power supply, set my meter to DCV. Place black probe on any ground and then the red probe I would probe the source pin on mosfet M3016. Should see Vin (i assume 19v?) next I'd check drain pin on M3016. If VIN is present then I'd move to drain on mosfet A5. If I see VIN here then I unhook power, drain caps and use continuity mode to find the next components in the circuit to test them.

If no Vin on drain of M3016 then I would probably just remove it and place a piece of solder between the drain and source pads and connect power again to see if A5 is working. If no VIN on drain of A5 after that then I would remove it next and do the same shorting of drain and source on its footprint and reconnect power. If pc comes on and acts normal I would replace them. If pc does not come on the you have more problems beyond your original assumption of it being the first couple of mosfets. Might be wise to check for shorts first before connecting power at at each step. When you have the mosfets off its good idea to test them just google or youtube "test mosfet with dmm" for several video's. If they are good then you may have problems with gate signals not being sent.
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Thread Starter

Clinteastwood1

Joined Apr 2, 2021
14
You're totally right, my measures using the diode mode were not good.
I took inspiration from the steps you suggested and measured the voltage at the entry mosfets and guess what everything is normal, I get 19v where it should be.
I also switched the multimeter to the ohmmeter mode and tested all te mosfets. Conclusion there are no short circuit in them, at least if detecting a little resistance means no short circuit (I get a few ohms in each of them).

On another forum some people suggested me to take other measures at the bios chip's pins, at the super IO chip, etc so I hope it will help me fix this laptop I really need it :(

I won't ask you more help since you told me you are not specializing in repairing computers, but I really thank you for all your help it means a lot to me.
 
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