820-00163 no backlight

Kyle93

Member
This arrived with no backlight and at a loss of what it could be.

Using one of our known good screens i do get 3.3V for image but 0v backlight. Both sides D7701 0V no shorts in diode mode. Also replaced U7701 and Q7701 but no change. F7700 is good.



U7701

pin 5 5v

pin 18 5v

pin 17 0v

pin 11 12.45v
 

2informaticos

Administrator
Staff member
Do you get internal image for sure?
Disconnect internal LCD and test again external video.

Check for USB activity.
Caps Lock reacts?
You may have GPU issue.
 

Kyle93

Member
I do get a chime when it first starts and GPU vcore is a steady .860V

No do not know if internal image is there for sure. I assumed with getting 5V and 3V from screen

no external video with internal LCD disconnect.

could It be faulty U9600 with pin 17 of U7701 0V?
 

2informaticos

Administrator
Staff member
Missing internal/external image at same time, points more to GPU problem; heat it for test.
Backlight issue cannot block external video.

Very low chance to be U9600, but you can change it (just in case).
Confirm USB activity after chime.
You should make an idea if board continues working, or just stuck after chime.
 

Kyle93

Member
Before heating GPU decided to try new bios just in case. Looks like old bios was bad. Now getting blinking light on usb drive and confirmed external image. still nothing on internal.

PP5VR3V3_SW_LCD now 0v

BUF_5V_EN only 0.34V
 

2informaticos

Administrator
Staff member
Both must appear at least in the first few seconds, when chimes.
LCD_HPD should go high at same time, to maintain the voltages.
 

2informaticos

Administrator
Staff member
I hope you've checked with screen connected.
In fact, LCD_HPD can't appear other way.

From previous post, I understood you got steady voltage.
Try other BIOS, known good.
 

Kyle93

Member
Url from paul no longer works.

Tried other bios from 00426 board thats fully functional. LCD_HPD is steady now and PP5VR3V3_SW_LCD back to 5V

Also have confirmed usb activity and external image

Still 0V on backlight
 
Last edited:

2informaticos

Administrator
Staff member
Did you test with compatible known good screen for sure?
Backlight adjust comes from T-CONN (I2C bus), placed inside LCD assembly.
 
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