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    #1

    Asus X409DL Rev 2.0

    Hey all,

    I've got an ASUS laptop (Asus X409DL Rev 2.0) that had a little liquid spill on it however the majority was on the daughter board for the I/O stuff which is connected over a ribbon cable which I have disconnected for now. A small bit of liquid did however get onto what schematics and boardview show is a DC step down IC; a Realtek RT8249CQGW - markings: 2N=. There is no short on the main power rail as I have 19v with the charger plugged in however I have no other power, standby or always on rails anywhere on the board. Looking at the datasheet for this IC I want to sanity check that I'm understanding it properly.

    Am I correct in reading for the C mode so long as this IC has a Vin voltage (pin 12 - I have 19v here) that reaches the threshold to turn on then the 3v always on should be present on LDO3? (Pin 3 - I have 0v here)

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    #2
    Correct.

    If LDO3 is @ 0v, either it is defective or being excessively loaded. Remove all power. Meter in resistance (not diode) mode. Measure the resistance of this LDO3 rail to ground. Post the measurement. It is also possible that a transient event has nuked this power rail and therefore this component must be replaced. Flux it well to remove.

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      #3
      Ok thanks for the clarification, wasn't sure if I was missing something with LDO3. That rail isn't shorted directly to ground however it is possibly being strange as it reads ~75k when I first put my probe on the pin and then takes about 10 seconds where it tops out at ~220k. I swapped the IC to a new one just in case the original one that got hit with liquid went bad however it's the same result.

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        #4
        Resistance to GND on LDO3 as wellas LDO5 should be measured. Resistance to GND on 3V/5V coils should be measured. Check caps around SIO for shorting. Does the 2N chip gets warm?

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          #5
          The 2N chip does not get warm, there isn't really any sign of heat anywhere with the charger plugged in. I do have a particularly low reading on a 3VA_EC (<1k) on the SIO. Is it likely that the SIO may have taken some amount of spike when liquid was on the 2N chip and that is what has gone.

          When I get chance I think it's safe to inject 1v onto that 3VA rail and see what current draw if any.

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