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LA-9865P boot/power looping

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    LA-9865P boot/power looping

    Background:
    Laptop came in as not powering ON (and seemed to have been worked on previously). It also had printer toner spilled all over it. Once opened, I saw that some printer toner made its way near ram slots, ODD and SOC.

    After removing the heatsink, it does not seem that toner got to the SOC (it was mostly on the heatsink). I cleaned it as much as possible using compressed air and a fine brush. Also avoided using any liquid to avoid clumping of the toner powder.

    After initial diagnostics, I found a defective mosfet (PQ205) and replaced it. I now have standby light but when I tried turning on, I get the first power cycle (ON-Off-On) but then it keeps cycling every 5 seconds or so for about 5 to 7 cycles and stays off (with no image). The same thing starts over again when power button is pressed.

    All voltage rails are present and stable while its ON. In off state I have stable 3.3 and 5V alwaysON voltage. CPU VCore is 1.75V and VGPU is 0.90V and stable.

    All power good/OK signals are present while all rails are on and stable.

    However, PLT_RST# is present only briefly (please see attached picture) and DIMM_DRAMRST# does not go above 0.72V (Neither PLT_RST# nor DIMM_DRAMRST# is shorted to ground).

    I checked R184 and it is fine. I have 1.35V on one side and 0.75V on DIMM_DRAMRST# side (It can be seen changing from 0V to 0.75V when power button is pressed though). VTT voltage is OK (0.68V)

    I also don't have any activity on PM_SMBDATA & PM_SMBCLK (they are constant at 3.3V). No activity on BIOS (Constant 3.3V).


    What I tried so far:
    1. Reprogram BIOS - Same issue
    2. Replaced EC - Same issue
    3. Tried known good RAM - Same issue
    4. Clean RAM slot with a bath of alcohol and medium hardness brush (I don't have ultrasonic (yet)) - Same issue
    5. Replaced just in case but no change.
    6. Tried with and without battery (battery charges fine by the way) - Same issue
    7. No shorts were found


    Motherboard: VSKTA LA-9865P Rev1A

    Do I have a bad/dead SOC? Please find attached schematic. MOD Edit: Schematic removed.
    Attached Files
    Last edited by SMDFlea; 09-14-2023, 01:35 AM.

    #2
    Re: LA-9865P boot/power looping

    Edit:
    Power draw @ 19.7V:
    1. 20mA standby when charger is first plugged in
    2. 282mA (with and without RAM) when turned on
    3. 10mA standby after a few cycles

    32.768KHz and 24MHz clock present and stable

    it keeps cycling every 5 seconds or so for about 5 to 7 cycles and stays off (with no image)
    correction: it keeps cycling every 2 to 3 seconds
    Last edited by Spider1211; 09-24-2020, 07:36 AM.

    Comment


      #3
      Re: LA-9865P boot/power looping

      Check U45 voltage.

      Comment


        #4
        Re: LA-9865P boot/power looping

        Already checked, all good there.

        Comment


          #5
          Re: LA-9865P boot/power looping

          Correction (Sorry, was short on sleep when writing original post)

          checked R184 and it is fine. I have 1.35V on one side and 0.75V on DIMM_DRAMRST# side
          Its not 0.75V but rather 0.12V. Resistance to ground on DIMM_DRAMRST# varies from 0.6KOhm to 0.76KOhm (same reading with or without RAM inserted)


          Measured on a donor board with different SoC and DRAMRST# is atleast 4KOhm.

          Comment


            #6
            Re: LA-9865P boot/power looping

            Originally posted by Spider1211 View Post
            Correction (Sorry, was short on sleep when writing original post)



            Its not 0.75V but rather 0.12V. Resistance to ground on DIMM_DRAMRST# varies from 0.6KOhm to 0.76KOhm (same reading with or without RAM inserted)


            Measured on a donor board with different SoC and DRAMRST# is atleast 4KOhm.
            Is it exactly a cpu problem? Or did you solve it? I'm in the same situation

            same dramrst# 0.6kohm

            Comment

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