820-00840 ( missing PANEL_PWR_EN)

I am working on a 820-00840-A "Came in for no backlight."

After a few quick checks the (PANEL_PWR_EN) out of U8501 never shows up. Not even for a split second. I know what part of the boot process it should show and it never does. On my reference board it does. My understanding is this should turn on and if the CPU does not get a response from the LCD or current draw is too high it will shut it down. The current draw circuitry is "No Stuff".
Then I checked. (EDP_PANEL_PWR_EN) input into U8510 and it never shows up. The power rails to these chips are present and normal.

The only thing in front of this is U0500 "the CPU" I don't suspect this part. I am lacking the understanding of this process to troubleshoot further.

Watching the board it does boot. Current draw pattern shows a booting board. Exact same pattern as my reference board. It even chimes like it is happy.
 
Not sure if my setup for testing that is working.

I have a USB-C HDMI adapter that also has two USB ports, TF and SD card reader with HDMI on the end. I could not get it to work so I put my test board in the MacBook and booted it up and also got nothing on my TV. I did get to the desktop. I don't have the user name or password for this machine as it came from a school. We usually use a USB test drive but that broke yesterday. It looks like I have to boot into the O/S before I can enable the HDMI port so not sure how to test this on a board that does not display a image.

I have not tried a USB mouse. Well I don't have one that blinks lights when you move it so not sure how to test that either.
 

2informaticos

Administrator
Staff member
You must get USB boot pendrive with Link LED.
If flashes, USB activity is confirmed 100%.
USB mouse is not always perfect confirmation.

If you get chime can trick you, as the board can get stuck immediately after chime.

eDP requires 3V3, or 5V in the first seconds present at LCD connector.
It should respond puting high DP_INT_HPD line.
Only then CPU knows the screen is connected.
 
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