820-00923 A1706 2017 No touchbar no video int/ext no caps light does flash USB thumb drive

[bradinboise]

Hello all,

So I spent a few days on this one following other suggestions found on this forum.

However I still cannot get video internal or external video, no chime, no touchbar, no caps light, but do have USB thumb drive led light flashing.

Intel CPU chip gets pretty hot.

Cannot see any evidence of liquid damage. No other history, other than the screen does have the flexgate issue because I hooked an 840 board to the screen and I can see the the apple logo but no backlight and both backlight cables look like they are broken inside.

I did find a shorted cap on the PP3V3_S4 line, replaced cap and now have 3.3v

I have all my rails from page 100 and 101 and checked all coils, and also load switches on page 78.

I was really hoping that cap was it, but no

So I just need some further checks that I might be missing before I condemn the CPU.

Thanks for the help.

 

[2informaticos]

What is the CPU core voltage 10s after starts?
Do you get USB activity for sure in all USB ports?
Any previous attempt repair done by someone else?

 

[bradinboise]

Thanks for the fast reply.

Please reference which cpu rail to check.

Yes, I get a blinking led on all 4 ports with thumb drive.

I cannot see any previous work on the board. It is really clean looking.

As a side note, I was trying to find on youtube last night any rossmann videos about this board that I might have missed. However I ran across this video that says there are 3 ways to check for a dead GPU on this board. I don't have an oscilloscope, but according to this guy in the video, my usb meter stops at .68v after "booting" and stays there and never changes. Is there any truth to what he is saying about diagnosing a bad GPU on this board? Just curious.

Thanks

 

[bradinboise]

Hello, any feedback or continued help would be awesome, thanks!

 

[2informaticos]

No video, but they forgot to say if no USB activity also.
Too many people consider only video when test a logic board.
If no USB activity, there can be anything, not related in any way with GPU; iGPU in this case.

LPC bus communicates PCH with SMC.
Failure communication can be caused by various reasons.

In your case, as you have USB activity, there should be a video problem.
The MLB boots at least, not only turns on.
As missing both internal/external video, this points to iGPU issue.
Should be very strange to have an internal video issue, plus a Thunderbolt problem; which will prevent external video.

When diagnose, should go for the most probably failure reason.