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Dell Latitude E7440 battery issue

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    Dell Latitude E7440 battery issue

    Dell Latitude E7440 LA-9591P. The laptop sees the battery, its health, determines the charge, determines the power supply. But the battery is not charging. If boot into Windows, the battery charge icon flashes, but the battery discharges. Changed the battery - same thing. Consumption 0.2A The laptop has a very intricate circuit, designed for the battery of the docking station. For me it's pretty hard to understand what exactly is responsible for the battery charge: charger IC or batfet, or some chain of ic+ mofet+resistors/capacitors

    #2
    Re: Dell Latitude E7440 battery issue

    Review the mosfet linked to the charger ic.

    Likely there will be 2 mosfets from dcin to the main power rail. Then 2 more mosfets that define the battery charge voltage (high side and low side). Finally the battery mosfet to allow the battery pack to power the laptop.

    Remove all power. No battery. Meter in resistance mode.

    Check the resistance across:

    Source (1-2-3) and drain (5-6-7-8)
    Source and gate(4)
    Gate and drain

    For each mosfet.

    Post each reading. If you see "1" or "OL" on your meter, raise the scale till you get a reading. Checking for a low resistance which means the mosfet is defective.

    PS: see the sticky above by @Piernov on the charging circuits. The above is a quick summary from that article.

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      #3
      Re: Dell Latitude E7440 battery issue

      There's almost 8V on battery + pin, when battery plugged in. But no charging. Due to the schematic, the motherboard have 65w 45w power supply protection. 65W is too much...looks like, it must work from 45w power supply? BTW now it works with DIY 180W power supply. Anyway, the current consumption 0.2A with battery, and 0.6A without
      Last edited by Sudoer; 04-26-2022, 07:40 PM.

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        #4
        Re: Dell Latitude E7440 battery issue

        Dells disable battery charging and throttle CPU if the one wire side of the charger isn't communicating (check in BIOS as to what is being seen). If it's unknown (and its an OEM charger), this is usually because the centre pin in the DC jack has collapsed. It can short 19V onto the one wire line, destroying the chip inside the charger. Sometimes you have to replace both to get it working.

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          #5
          Re: Dell Latitude E7440 battery issue

          It's DIY charger with one wire chip, BIOS see it like 180w charger. And battery, and discharge battery. But not charging. It's 4-th E7440 in my lab, haven't seen problem like this before.

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            #6
            Re: Dell Latitude E7440 battery issue

            Use a genuine 65W/90W charger whichever is specified for this model. Dell's adapter is problematic 'coz of PSID circuit. So first make sure its not the adapter.

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              #7
              Re: Dell Latitude E7440 battery issue

              Solved. The problem was with EC. Replaced, flashed. Works. Profit.
              Have another two LA-9591P mobos. Won't power on. There's 3 and 5V powered up, but no 3V on flash memory. In this case, check U45 3rd and 5th pins with oscilloscope. If you see sawtooth waveform - replace ECE5048-LZY, because the EC do not send signal to open U45 and U45 powered flash memory.
              Last edited by Sudoer; 05-02-2022, 03:42 PM.

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                #8
                Re: Dell Latitude E7440 battery issue

                Originally posted by Sudoer View Post
                Solved. The problem was with EC. Replaced, flashed. Works. Profit.
                Have another two LA-9591P mobos. Won't power on. There's 3 and 5V powered up, but no 3V on flash memory. In this case, check U45 3rd and 5th pins with oscilloscope. If you see sawtooth waveform - replace ECE5048-LZY, because the EC do not send signal to open U45 and U45 powered flash memory.
                How do you understand the problem was the EC chip? With the oscilloscope?

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                  #9
                  Re: Dell Latitude E7440 battery issue

                  Originally posted by giulio93 View Post
                  How do you understand the problem was the EC chip? With the oscilloscope?
                  The good signal should be looks like this one


                  And this one - what I see on the bad EC

                  Attached Files

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