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820-00281 u9850 no internal display

T

ThisIsWes:AASP

Member
External display worked but nothing on internal. Pin 43 and 1 of the display connector appeared burnt. I've resolved this a few times before with replacing u9850.

This time I replaced u9850 and tested with the display - nothing. Removed the connector and noticed further burning around 43 & 1 of the display board connector and cable. Assuming there was still a short someone after the display cable.

Replaced u9850 again and tried a fresh cable and known good display - nothing again. Replaced u9850 a second time with the same result.

I've read but never experienced u9800 also failing with u9850. Is it possible I fried this too or something else?
 
2informaticos

2informaticos

Administrator
Staff member
Did you replace LCD connector and tested with full LCD assembly?
Check the other connector, where the onboard small cable goes, in the bottom case.
Also check diode mode to ground on EDP data lines lines of J8500.

Are you missing image too, or backlight only?
Do you get PP3V3/5V_S0SW_LCD?
DP_INT_HPD goes high?
 
T

ThisIsWes:AASP

Member
DP_INT_HPD does not do anything with board only connected to power, no disp. What is this?

By connector do you mean J8500 or the flat cable? At first I did not replace the cable but after the first attempt I did replaced the flat cable that connects to j8500 and tested with a complete case. For initial testing I just place the board in and connect USB-C ports and display. Tried 2 working displays.
J8500 looks perfect, no burn.
No image/backlight

1) EDP_AUXCH_C_N - 0.493
3) EDP_AUXCH_C_P - 0.465
7) EDP_INT_ML_N<0> - 0.378
9) EDP_INT_ML_P<0> - 0.376
13) EDP_INT_ML_N<1> - 0.376
15) EDP_INT_ML_P<1> - 0.376
19) EDP_INT_ML_N<2> - 0.376
21) EDP_INT_ML_P<2 - 0.376
25) EDP_INT_ML_N<3> 0.376
27) EDP_INT_ML_P<3> - 0.378
4) BUF_EDP_PANEL_PWR_EN - 0.730

PP5V_S0SW_LCD - 5.128v
PP3V3_S0SW_LCD - 3.3v

DP_INT_HPD - 0.0v
 
2informaticos

2informaticos

Administrator
Staff member
"DP_INT_HPD does not do anything with board only connected to power, no disp."
Normal, it comes from LCD...

ALLWAYS check voltages with LCD connected, when you diagnose internal image/backlight problem.
Check for pulse at EDP_PANEL_PWR_EN and look for reaction at DP_INT_HPD_R at same time.
 
T

ThisIsWes:AASP

Member
with disp connected after about 15 seconds I get the following:
EDP_PANEL_PWR_EN - 3.283V
DP_INT_HPD_R - 3.259V (this one was hard to measure..)

Not a pulse but steady values.
 
2informaticos

2informaticos

Administrator
Staff member
If DP_INT_HPD_R stays high, internal LCD should be recognized by PCH.
BUF_EDP_PANEL_PWR and DP_INT_HPD must be high too.

Diode mode difference between EDP_AUXCH lines looks too high.
 
2informaticos

2informaticos

Administrator
Staff member
If difference only when LCD connected, then display issue, or video cables.
If is always big difference, then U9850 problem...
 
T

ThisIsWes:AASP

Member
With known good LCD, new disp cable, new u8950 - values before and after power applied. Still no backlight/img.

1 EDP_AUXCH_C_N - 0.676 > 0.685
3 EDP_AUXCH_C_P - 0.686 > 0.698
7 EDP_INT_ML_N<0> - 0.392 > 0.395
9 EDP_INT_ML_P<0> - 0.390 > 0.392
13 EDP_INT_ML_N<1> - 0.392 > 0.395
15 EDP_INT_ML_P<1> - 0.392 > 0.393
19 EDP_INT_ML_N<2> - 0.390 > 0.391
21 EDP_INT_ML_P<2 - 0.386 > 0.388
25 EDP_INT_ML_N<3> 0.390 > 0.393
27 EDP_INT_ML_P<3> - 0.388 > 0.391
4 BUF_EDP_PANEL_PWR_EN - 0.720 > 0.730
 
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