SOLVED - 820-00840 A1708 shorted U2800

[jadao]

No water damage, this board was not powering up because it had PP0V9_TBT_X_SVR and PP3V3_TBT_X_S0 shorted to ground.
Removed R5640 to isolate PP3V3_S0 and board powered on fine and charged great but obviously no usb Data or HDMI output.

I replaced U2800 with a preballed one and put back R5640, I have no more shorts but still no hdmi output and no usb data. In the EFI boot menu I can see my external usb drive...

I am thinking to grab a U2800 from a donnour board and reball it (got finally the stencil). Thought maybe these chip come with some firmware...

Is there anything else I can check before I replace the chip with an A1708 donnour one?

Thanks

 

[2informaticos]

If you can see external disk on boot menu, can you start from it?
Under macOS, did you check both USB2/3 modes?
The USB-C redriver chip looks good?

 

[jadao]

No I can't start from the external disk on boot menu. When I start an external disk OS I see the apple logo with the progress bar at let say 60% and I get the Apple prohibitory sign, tested with different volumes (Catalina, High Sierra and Mojave) they all finish with the prohibitory sign. I tried also to load external macOs with a 2.0 and 3.0 USB drive and same thing.

Yes under Macos with internal ssd I tried both USB 2.0 and 3.0 no one show up on the desktop, checked also in disk utility no disk is detected.

For the redriver USB-C chip: if you are talking about the PI3USB3224BXEAE ic that doesn't exist on the 820-00875 board view I have visually nothing to say about it.

 

[2informaticos]

You've said to have 00840 board.
That chip doesn't appear on schematic, nor boardview; but is present on the board.

USB mouse is working?

 

[jadao]

Yes i have 00840 board with the chip present and it looks good. And am using the 00875 schematic and boardview on witch the chip doesn’t appear.

USB mouse is working only on the boot menu same as the detected external usb boot drives.
When the MacOS is launched the usb mouse is disabled.

 

[2informaticos]

Then you have problem with SPI mode of trackpad.
Check diode mode to ground on TPAD_SPI lines; may have a protection diode damaged.
Also check the pull-up resistors, page 16.

 

[jadao]

I’ve just compared diode mode values for tpad_spi lines with known working board and they are the same.

Pull-up resistors related to tpad on page 16 are all within specs according to values shown on schematic.

Should I replace again U2800 or that has nothing to do with HDMI/usb disabled on spi mode?

thanks

 

[2informaticos]

U2800 has nothing to do with TP-PCH communication.
Check TPAD_SPI_CS_CONN_L voltage; logged into macOS, with TP connected, of course.

 

[jadao]

I soldered a wire from J4801-pin 13 and I am measuring 3.3V on TPAD_SPI_CS_CONN_L with trackpad connected while logged in macOS.
Just in case I tested with another set of trackpad and flex cable and I have the same results.

 

[2informaticos]

Sorry man, I just saw your problem is with USB mouse, not internal.

Something happens when macOS start to load the drivers.
That explain the prohibited sign; because system lose communication with external disk.
U2800 may affect the communication.

Check starting in Diagnostic mode is any error pops up.

 

[jadao]

Oh no problem at all.

I was able to simulate the same issue with a known working board by preventing PP0V9_TBT_X_SVR and PP3V3_TBT_X_S0 to feed U2800, I had the exact issue. Suprisingly nothing is reported in diagnostic mode.

So I just reballed an another U2800 from a donnor board and problem is solved now!
The preballed chip I had was either bad or just bad reballing, found it more difficult than Gmux on A1286!

Thanks for your support!

 

[2informaticos]

Thanks for feedback.
This can save time for other forum members, in the future.