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820-00840, Liquid, Powers with high fan, no boot.

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  • 820-00840, Liquid, Powers with high fan, no boot.

    Working on a 2nd 820-00840 with very similar symptoms, but this one had liquid.

    -- PPBUS is present at 13v
    -- ALL_SYS_PWRGD is present at 3.3v
    -- 3v3_s0 and 5v_s0 both present and proper
    -- All CPU and memory rails I've checked all appear to be present and correct voltages.
    -- Board powers on, fan slowly gets up to full speed and there's no booting or other activity.
    -- No light on USB mouse when connected via USB-C --> USB adapter
    -- Should I try to load a different BIOS?

    A few general questions with regards to this model: What specific things could cause this model to run the fan at full speed? I have two boards now that do this, and I'm wondering if another component (trackpad, trackpad cable, etc) is the cause. Unfortunately I do not yet have another test assembly, which is a bummer because it would help to know if this tpad is good or not. I hate not having any sort of indication of chime or anything.

    Any advice appreciated as always.


    - - - - - - - - - - - -

    UPDATE: After resolving the high-fans (trackpad cable not fully connected on tpad-end), I have some more information:

    Unit powers and forcetouch activates and stays on until power is removed. However, no activity on USB drive (with power light) when connected via USB_C adapter.

    Any advice on where to go from here appreciated.
    Last edited by SMMRepair; 09-25-2018, 06:32 PM.

  • #2
    OK, I actually found that the trackpad cable was a bit crooked and not completely connected. I re-seated it (it appears to have been replaced at some point), and now the fan is not turning on, and the forcetouch actually works when the unit turns on. Now I just have no video and no light on a USB mouse when connected via USB-C --> USB adapter. Also no activity on a USB drive with light when plugged in, but ForceTouch trackpad remains "on" until power is removed.
    Last edited by SMMRepair; 09-25-2018, 06:31 PM.

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    • #3
      Inspect for water damage on all USB-C drivers, if one dont work none will work, also check for water damage on display connector and cable....

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      • #4
        Thanks, Aprendiz. If I have ppbus at 13v, does that not eliminate the USB-C drivers? Or could one of the drivers still be bad despite the board powering on (and trackpad clicking)? Display connector and cable both good. This is a board-only sent in to us for repair, so we're using our own test assembly.

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