Asus ROG ga401IV motherboard - AC Short Protection resistor getting hot

[gaelican]

Hi,

I am working on an Asus ROG laptop repair. I was able to find that there is a short on the motherboard, and the 20 volts from the charger only gets to the first mosfet before disappearing.

When looking around with a thermal camera, I noticed the chip marked "14C" in the picture was getting warm. Nothing else was receiving heat.

I found a boardview diagram and schematic for a motherboard that looks nearly identical, that has the same component. This appears to be marked as "AC Short Protection" with a value of 13.7KOhms.

My question is, does this mean that the charging port/cable is shorted, or is the component itself is bad? I tried multiple chargers which are good, and the result is the same. The port doesn't have any visible damage either. If it is the resistor that's bad, would it work to just replace it with a regular resistor that has a 13.7KOhm value? Another important detail is that it is still measuring pretty much at that value, that's why i'm not sure if it is bad.

[mon2]

Do you have a schematic for this board? Found only a boardview file in my database. Link it if available but only in the schematic forum.

The fault will most likely be with the DCin mosfets and not this resistor. Which charger IC is onboard? Which mosfets are in the power path. Each mosfet should be reviewed for a short condition.

Test with no power to the board. Meter in resistance mode.

Measure the resistance across the mosfet:

source / drain
source / gate
gate / drain

Each measurement should be hundreds of k ohms or higher. Otherwise, the mosfet may be defective.

[gaelican]

I do not have a schematic from the forum unfortunately. I measured the two mosfets near the DCin and they do not appear to be shorted as all the measurements are in the hundred kohms or higher. I'm not sure how how to identify the charging IC for certain but I believe it might be the 6s30a chip. I have found some shorted capacitors close to where the mosfets are, but when I try to inject voltage the only thing that gets warm is whatever I'm injecting into.

[mon2]

Share pics of the area starting at where the DC power jack enters the board. The DCin mosfets will be in the path and eventually reach the charger IC. The charger IC may be the TI BQ series. Post pics on that part as well for a review.

In your mosfet testing, you have tested each permutation as noted above?

[gaelican]

I did test the mosfets as instructed, though I do still mix up the names of all the parts. The second one when measured against ground does appear shorted but when measured by itself seems fine. What would be the best way for me to try to isolate the faulty part? I have a voltage injection tool and a thermal camera however I haven't been able to reveal anything with them.

[gaelican]

Nevermind, I checked again and was able to find the faintest bit of glow on one of the cpu mosfets :/ checked like 10 times before and could not notice it somehow. I do appreciate all your help though.

[pc_okay]

Hello,

Good to know: 14C is just a standard resistor using EIA 96 marking. (a marking standard for CMS).
14C = 13.7Kohm
https://kiloohm.info/eia96-resistor/14C

A failing resistor may just block current not specially heating, BUT your resistor may fail one day if it heat too much. 😁
Your resistor heat because a lot of current pass through this resistor (it's a symptom not a cause) maybe because you had a short somewhere and PD9002 was protecting your circuit. (i still don't get exactly how...)

[mcplslg123]

The chip marked6s30a is not the charging IC. It should be very likely BQ24780S.

Measure resistance to GND on CLR located just after the two dc-in mosfets.

Too me it seems your 19V line is shorted to GND perhaps due to high side mosfet getting short on cpu core area.

This is the most common fault on gaming laptop.

First confirm whether my doubt is genuine and if so, i'm afraid your cpu is already fried.