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

[SMMRepair]

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.


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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.

 

[SMMRepair]

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.

 

[aprendiz]

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....

 

[SMMRepair]

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.