820-00923-A won't turn on


New member
So this is an A1706 Touchbar and I'm stumped. Here's what I know.

I'll preface by saying when I purchased the board, I saw that R6907 and D6902 were physically damaged (burnt on the top). I replaced both of them with exact replacements. That was the only visible damage I could find after inspecting every component with a microscope. There are no shorts to be found.

When you plug in the board, it communicates with the charger, and we see 20V. It's drawing 200mA, but never more. PPBUS_G3H is good throughout the entire board, all of the 3.3v lines are good, there are no shorts on any of the power systems, so I'm at a loss! All the information online is about fixing the 3.3v lines or the CD3215 chips, or stupidly obvious shorts in components.

The only strange thing I noticed is that there is 8.3V on P3V3G3H_VBST which comes out of U6903 which is directly connected to the burnt components I replaced. I figured P3V3G3H_VBST would be a 3.3V line based on the name. But on the other side of C6907 (pin 2) we're back to 3.3V, which electrically confuses me. This made me think maybe U6903 was toasted, but it's happily outputting 3.3V.

What do I do!?
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Staff member
First of all, welcome to the forum!

"I figured P3V3G3H_VBST would be a 3.3V line based on the name"
Wrong assumption; try not making more in the future.
VBST in the name, means is the boost line; should be (Out voltage + 5V) approx.

You didn't say anything about the voltage detected on the big coils.
If you get correct voltages, check for USB activity and external video.