820-3536 no image, got chime and fan spin

[ajdoc]

Liquid damage board around J8300
J8300 replaced as pin 3 was burned out.

Got chime, fans spin, USB light but no image.

PP5VR3V3_SW_LCD got 5V

LCD_HPD_CONN got
Resistors around U8340 and U8340 are OK.

Any idea?

 

[2informaticos]

"LCD_HPD_CONN got" 0V, or 2.5v???
We need to know DP_INT_HPD level.

Do you miss image and backlight too?
Did you check all the traces between J8300 and all C832x caps?

 

[ajdoc]

DP_INT_HPD got 3.33V

Miss image and backlight.

All traces between J8300 and all C832x caps got continuity.

 

[2informaticos]

Check external video.
Post U7700 and U8330 voltages.

 

[ajdoc]

No video on ext display - those DP ports are not looking good

U7700/1 0.25V
U7700/2 0.25V
U7700/4 0V
U7700/5 5.13V
U7700/6 5.12V
U7700/8 5.10V
U7700/9 12.59V
U7700/10 12.59V
U7700/11 12.16V
U7700/12 0V
U7700/13 1.12V
U7700/14 jumping from 0.75V-1.75V
U7700/15 5.12V
U7700/16 5.13V
U7700/17 0V
U7700/18 5.13V
U7700/19 1.75V
U7700/20 1.19V
U7700/21 jumping from 0.20V-0.58V

U8330/1 0V
U8330/2 0V
U8330/3 0V
U8330/5 0V
U8330/6 0V
U8330/7 0V
U8330/8 3.33V

 

[JohnB8812]

Try external from HDMI to hell with TBT.

 

[ajdoc]

On HDMI all good.

 

[JohnB8812]

Ok tried known good display assembly?

 

[2informaticos]

"U7700/17 0V"
Missing enable signal for backlight.

"PP5VR3V3_SW_LCD got 5V
---------------------
U8330/3 0V"
This is not possible, unless U8300 is shorted.
EDP_PANEL_PWR_OR_PSR_EN is required to enable 5V on pins 28-30 of J8300!!!

If you checked these voltages without LCD connected, NOT good.
Check all again; less keyboard backlight signals/voltages (not needed).

 

[ajdoc]

I replaced U8300 had back 3.33V on pin 3.

Tested with another display and had image but no backlight.
J8300/1 0V.
J8300/10 3.33V
J8300//30 5V

The issue was with two traces on J8300/3 and J8300/4. Both Had 0V. Jumpers from other side of the board.
5V was back on both pins and got backlight.

Maaany thanks guys for tips