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dell latitude 7490 la-f322p no power

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    dell latitude 7490 la-f322p no power

    this board does not seem to have a short to ground. 19 volts gets to the current sensing resistor. 12 volts is on the battery terminal. there is 0v on the battery smbus but i don't have a battery for it and that might be the issue. will someone tell me whether this board needs a battery installed to power up?

    #2
    Re: dell latitude 7490 la-f322p no power

    Nope. All laptop mb will work in ac adapter mode(without battery).So to powerup, battery is not needed.Btw, if you have 0 volts on smbus that indicates perhaps absence of 3v LDO. So do check your 3V PWM regulator's requirements and measure the resistance on 3V LDO.

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      #3
      Re: dell latitude 7490 la-f322p no power

      gettin 0v on 3v5v_en with comes from alwon. what is alwon

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        #4
        Re: dell latitude 7490 la-f322p no power

        ALWON=Always On. This signal comes from SIO and is needed to get output on 3/5V coils. But first you need to get 3V LDO. The PWM regulator will generate it without ENABLE signal.

        What is the voltage and resistance on 3V LDO??
        Last edited by mcplslg123; 12-01-2021, 11:03 PM.

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          #5
          Re: dell latitude 7490 la-f322p no power

          the sio which is a bga package appears to the issue. rtc_cell has a short to ground and i ran 1v through its path and the EC lit up like a christmas tree on the thermal camera. i would reball it but i'll assume that it's dead since i reflowed it real good and nothing changed. the chip is mec5105

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            #6
            Re: dell latitude 7490 la-f322p no power

            is reprogramming easy enough? i know how to reprogram a bios

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              #7
              Re: dell latitude 7490 la-f322p no power

              A shorted ec needs to be replaaced , not reballed. Its bit difficult to program these bga ec.

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                #8
                Re: dell latitude 7490 la-f322p no power

                well i replaced the sio with a new one and the short on +rtc_cell is back. is measures 1.1 ohm resistance to ground
                Last edited by kjchatman; 12-24-2021, 03:06 PM.

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                  #9
                  Re: dell latitude 7490 la-f322p no power

                  Originally posted by kjchatman View Post
                  well i replaced the sio with a new one and the short on +rtc_cell is back. is measures 1.1 ohm resistance to ground
                  Hi kjatchman,
                  I have exactly the same issue - +RTC_CELL shorted to the ground (~1 Ohm) and no ALWON signal. I haven't done a short-circuit test yet because I don't have a thermal camera, I need to borrow.
                  Have you solved this problem on your laptop?
                  I would appreciate any advice

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                    #10
                    Re: dell latitude 7490 la-f322p no power

                    Short on RTC is usually related to shortedRTC section of PCH . Trace this signal to PCH and check resistance there. If you are lucky,it can be a shorted cap on the backside of SOC but very unlikely.

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