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820-2936-B Battery not recognized

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  • 820-2936-B Battery not recognized

    I have a 820-2936-B board which was completely dead. There was a short on PP3V42_G3H, which was a short internally in the ISL. Replaced the ISL and the system booted.
    But now it doesn't run on battery, and the system doesn't recognized a battery. The battery that was present was at 0V, so completely dead. Replaced with a known working battery, but still doen't see the battery.

    With just the battery connected I am getting PP3V42_G3H, but nothing else.

    On the battery connector (J6950) I am getting 3.42V on SMBUS_SMC_BSA_SCL (pin 4) and SYS_DETECT_L (pin 5), but 0V on SMBUS_SMC_BSA_SDA (pin 6).
    So the clock for communication is likely present, but doesn't want to talk. Not sure what SYS_DETECT_L does, since is just seem to be a dud.

    Since the ISL was shorted and likely drained the battery completely there might have been 10.5V on the SMBUS_SMC_BSA_SDA, and damaging the SMC. I measured the SMBUS_SMC_BSA_SDA line form U6950 to the ISL, which is not broken. SMBUS_SMC_BSA_SDA measures 0.480V to ground in diode mode, so seems there is no short.

    Just to be sure I had a good ISL, I replaced it by another new one, same issue.

    Are there anymore things I can try before concluding the SMC is "dead"?

  • #2
    SCL/SDA lines must have less than 1% difference in diode mode to ground; check that (red probe to ground).
    Don't forget to disconnect BIL connector, if get bigger difference, or if still get 0V on SDA line.
    D6950 should be removed too; in case of bad measurement on battery bus.
    But first of all, check R5280 integrity.


    • #3
      Checked R5280, seems fine (1990 ohms, should be 2k). Strangly enough I now have 3.42V on SMBUS_SMC_BSA_SDA, and 0.26V on SYS_DETECT_L. I'm a 100% sure it wasn't like that before. Still doesn't recognize or run on the battery tho.

      Measurements before removing D6950:
      SMBUS_SMC_BSA_SDA 0.465V
      SMBUS_SMC_BSA_SCL 0.451V

      After removing D6950:
      SMBUS_SMC_BSA_SDA 0.445V
      SMBUS_SMC_BSA_SCL 0.458V

      The measured values on diode mode very slowly rise while measuring. These values are after about 1 minute of measuring, and seem pretty stable.

      What does it imply that the values are more that 1% different from each other tho?


      • #4
        SYS_DETECT_L should be low as correct.

        Let the board to cool before measuring diode mode on battery bus.
        Strange to get SDA, then SCL with lower value than the other line...
        Allow 20-30s after power is removed, for any continuity (diode mode, ohm mode) checking.

        Put good flux and reflow SMC.
        If still no battery recognized, change SMC.
        You can try reballing it first.


        • #5
          Reflowed the SMC, no change. I don't have a donor board for this, and not sure if it's worth it buying one for this old machine.

          I searched for the SMC itself (F2117LP20H) on Ali and Ebay, but pretty sure all the ones I found don't have the firmware in them. Do you know of a place where I can just buy the SMC?

          I'll try reballing the SMC tomorrow, but I have this feeling it's fried because 11V from the battery that probably got on the SMBUS_SMC_BSA_SDA line.


          • #6
            Such high voltage fried SMC for sure.
            But normally this should be visible as abnormal resistance to ground on that line.
            If you already removed/replaced D6950 and changed ISL6259, then only SMC remains...

            Look on galaxyelectronics2015 eBay store; he has very good price for scrap boards.
            I mentioned him several times in the forum, including Skype details.
            Do a search on the forum, if you are interested...


            • #7
              I ordered a donor board from him. Was $15 including shipping, so very good price. Just takes a month to get here
              This will have to be continues at a later date I guess.

              Thanks for sharing your knowledge 2informaticos, really appreciate it


              • #8
                Before changing SMC, be sure no overvoltage on SCL/SDA lines when battery is connected...
                Rest of liquid spill under battery connector can easy kill the SMC.


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