Asus ZenBook 13 UX333F External Short - Fast Battery Drain - Need Help

[jkucukov]

I'm trying to see if someone could help me with my Asus Zenbook 13 UX 333F with given symptoms that I've experience during a recent external short.

During last laptop charge, as I was moving the DC power supply, I caused the two leads (+ -) to touch. After that event the laptop stopped charging and pulling amps form the power supply. The only way the laptop will come on is with the power supply connected and the battery having some charge to it, battery drains immediately after short operation (it gets to Windows log in screen before it shuts off). The laptop would power on, show orange & white light from the left side and shut off after the battery would drain itself due to an assumed short on the motherboard.

I opened the laptop thinking I could do some practical diagnosis, I only see that the 19V of power comes through the DC jack and the closest mosfet is seeing 19 V on the top side while the main power rail sees a voltage range from 2.15 to 2.22V.

I've taken out the motherboard and have typed my discoveries on the images for the front side and back side of motherboard. Both sides of the motherboards have 1 faulty capacitor. I'm curios if the 2 bad capacitors discovered could lead to the symptoms that I'm seeing. The bad cap on the front side is close to the inductor that has continuity, that's close to the CPU. I'm tempted to remove the cracked capacitor from the front to see if the continuity from the inductor will disappear, any thoughts?

[mon2]

The pcb pads will always be larger than the solder legs of the device. The minor dimension difference should not affect the soldering of the replacement parts. However, the use of a 3*3 mm device will be ideal. Also the other devices have the ability for higher current support.

[jkucukov]

Resistance values from Power Mosfets:

1st mosfet, front side of MB

Source <> drain = the resistance climbs in megaohms range
source <> gate = the resistance climbs in megaohms range
Drain <> gate = 35.7 Ω

2nd mosfet, back side of MB

Source <> drain = 84.8 Ω
source <> gate = 120.4 Ω
Drain <> gate = 35.1 Ω

[mon2]

Flux and remove the 2nd mosfet. While the 2nd mosfet is off the board, measure the resistance again of the 1st mosfet. Is the drain / gate still this low of a resistance? If yes, that mosfet is also defective.

2nd mosfet is for sure defective.

Do measure the resistance to ground of the main 19v rail to check if there is a shorted part on this main rail.

[jkucukov]

Flux and remove the 2nd mosfet. While the 2nd mosfet is off the board, measure the resistance again of the 1st mosfet. Is the drain / gate still this low of a resistance? If yes, that mosfet is also defective.

2nd mosfet is for sure defective.

Do measure the resistance to ground of the main 19v rail to check if there is a shorted part on this main rail.

I confused drain and source sides of the mosfet sides last night, the way I'm taking measurements is red lead is on the source and black lead is on the drain (Source <> drain)

Here are the updated mosfet values:

1st mosfet, front side of MB

Source <> drain = the resistance climbs in megaohms range
source <> gate = 35.7 Ω
Drain <> gate = the resistance climbs in megaohms range

2nd mosfet, back side of MB

Source <> drain = 88.3 Ω
source <> gate = 35.7 Ω
Drain <> gate = 120.4 Ω

Im noticing that the source <> gate between the two measure 35.7 Ω which should be good now, right?

[mcplslg123]

PIN1-2-3=Source
Pin4=Gate
PIn5-6-7-8=Drain

The reading indicates a shorted mosfet for sure. Follow @mon2's advice on post#3

[jkucukov]

PIN1-2-3=Source
Pin4=Gate
PIn5-6-7-8=Drain

The reading indicates a shorted mosfet for sure. Follow @mon2's advice on post#3

I need to buy a hot air station. Right not the main power rail has a high Mega ohms range with the bad Mosfet. The bad mosfet reads A5 VNA 8V0303, looking for it on google doesn't produce the exact match, is there a compatibility site I can be using to find an equivalent? Where would be the best place to find these replacement mosfets?

[mon2]

Post a clear pic of this mosfet. Which charger IC is nearby these mosfets? Post a pic of this part as well. It may be the 'BQ24780'

[mcplslg123]

The mosfet is likely P0903BEA

[jkucukov]

Post a clear pic of this mosfet. Which charger IC is nearby these mosfets? Post a pic of this part as well. It may be the 'BQ24780'

Here is the picture of the front of the Board, 1st mosfet (M3056M 841 46E) with:
Source <> drain = the resistance climbs in megaohms range
source <> gate = 35.7 Ω
Drain <> gate = the resistance climbs in megaohms range


Here is the image from the back side of the bard with as you said the bad mosfet (A5 VNA 8V0303):

Source <> drain = 88.3 Ω
source <> gate = 35.7 Ω
Drain <> gate = 120.4 Ω


I took another photo showing the proximity of the BQ24780 in relation to the 1st mosfet (M3056M 841 46E) on the front side of the MB:

[mon2]

The smaller N-channel mosfet is most likely the one that is attached and is from Panasonic. This part is of an oddball physical size with 2.9*2.8 mm dimensions.



This part is no longer in production but you may be ok to replace it with perhaps a slightly weaker part.

This is part # AON3414 from Alpha & Omega

https://www.digikey.com/en/products/...ON3414/5209634

Drop in replacement and also ~3.0*3.0mm in size; same pinout and no metal belly which may be required for your PCB layout. That is, other grades of similar parts will be pin-for-pin compatible but are with metal traces on the part on the bottom side of the mosfet. These exposed traces can and will short other traces on the PCB unless they are masked - kaptop tape? Just some ideas.

If yes, then consider to flux and remove this suspected bad mosfet. Then test if the resistance changes to a normal range. If not, then the other mosfet is also a suspect. Do test the removed parts for their resistance when on your bench.

For any mosfet that needs to be replaced, study the PCB layout and share more pics. We cannot have traces shorting to the mosfet(s). Do note that the 2 DCin mosfets are of different physical sizes. If necessary, replace them both. Unable to find this smaller mosfet on Aliexpress - had a match with this part number to some big booty blue color tights. Interesting.

[jkucukov]

it seems the Mosfet is by Unikc, I found it on this Turkish site saying that A5 is the product while the 3 letters after are indicative of product date: https://www.atombilgisayar.com/a5-p0...SVbQTPva5ELj4T

[jkucukov]

Here is the data sheet of the A5 P0903BEA from Unikc

[mon2]

My largest concern if the underside metal portions of the package. If indeed your part on the board has the same metal pads then we are fine to consider many other parts. You do not need to source the part from offshore or Turkey, etc. There are other devices on Digikey / Mouser / Arrow that are this physical size and similar or of better quality than the original.

Here is a good alternative (with a metal belly like the referenced part):

https://www.digikey.ca/en/products/d...ON7528/3603570

Before ordering the replacement, suggest to flux and remove this part to confirm this is the only defect in the power path. Perhaps the other Dcin mosfet will also have some issues and needs to be replaced. Also available from DK or similar.

[jkucukov]

My largest concern if the underside metal portions of the package. If indeed your part on the board has the same metal pads then we are fine to consider many other parts. You do not need to source the part from offshore or Turkey, etc. There are other devices on Digikey / Mouser / Arrow that are this physical size and similar or of better quality than the original.

Here is a good alternative (with a metal belly like the referenced part):

https://www.digikey.ca/en/products/d...ON7528/3603570

Before ordering the replacement, suggest to flux and remove this part to confirm this is the only defect in the power path. Perhaps the other Dcin mosfet will also have some issues and needs to be replaced. Also available from DK or similar.

Yes, thank you. I have placed the hot air station from Amazon, will have it delivered by Wednesday. Once I receive the station I will get the mosfet removed and take photos, I have a hunch that there is the metal underside on the drain side. The Turkey site is just what had the explanation of the top side characters, once I knew A5 was the product by Unikc there were many options state side. But I wont make any hasty decisions just yet, I'll present the findings once that mosfet comes off.

[jkucukov]

Hot Air Station is in!

[mon2]

Looks the same as ours. Wait…is mine missing???

[jkucukov]

Looks the same as ours. Wait…is mine missing???

Lol, may as well be, it came from Ontario CA

What temp and air settings to get the mosfet off without causing damage to the traces, the videos make it look so easy.

[mcplslg123]

try with temp at 380-390 with airflow at level 3-4.

Use good quality flux to remove the smd part.

[jkucukov]

try with temp at 380-390 with airflow at level 3-4.

Use good quality flux to remove the smd part.

The machine I have has airflow settings in Liters / minute it goes up to 120 L/m. What would be corresponding airflow for that temp range?

[mon2]

Review the flux options from Mobile Sentrix:

Search results for: 'flux'

Also purchase some kapton tape to assist with protecting any nearby parts that may melt or warp with the hot air. For some cases, you may want to use a metal bracket (like the style used on computer PCs as filler plates) to protect parts. The plate will act like a protective heat shield but of course keep the air nozzle away from the areas to be protected. Keep the air pressure as low as required for the job else tiny parts can fly off the board into the twlight zone.

Suggest to purchase a donor board to experiment with for the process of soldering and desoldering with the new tool. The actual settings will vary with the # of PCB layers which will act like massive heatsinks so you may have to increase the temp on some boards (8L) while keeping the temp lower on others (4L).

Personally like to use 350-425 (often) with 40-70 air flow. Need to be cautious to not burn out the PCB nor the part.

We recently purchased a TBK Laser soldering station. Met them in HK and they had a show special offer that was too tempting. The laser has its purpose but as noted, it too can fry the part just through soldering if not careful with the settings.

Invest in some tweezers as well. The flux we are using is Amtech (believe they are clones and not the real deal but Mobile is probably selling the real product) and Mechanic brand (sourced through Mobile).

Watch the many good videos on YT to get some details on the full process.