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820 4924 no internal display

E

EJS

New member
820 4924 no display on LCD, machine does have display via HDMI out. EDP_BKLT_EN, LCD_PSR_EN, & EDP_PANEL_PWR all missing. I do have PP3V3_S0_PCH_GPIO going into U8330.
 
2informaticos

2informaticos

Administrator
Staff member
eDP requires some voltage presence in order to put high (2.5V) LCD_HPD_CONN signal, if connected of course.
Do you get something at pin5 of J8300?
Or pins 28-30 few seconds when the board starts...
 
E

EJS

New member
Pins 28-30 get 5.15v, Pin 5 gets .040v for a few seconds when the board starts, then drop to 0v.
 
E

EJS

New member
Yes confirmed correct 2015 known good working screen has been tested, still no display. This board looks clean as a whistle, as far as I know the display just randomly stopped working.
 
D

dukefawks

Administrator
The 5V on pins 28-30 suggest that the LCD is recognized if the 5V does not drop off again. Are you sure this is not just a backlight issue?
 
E

EJS

New member
Yes I'm sure, I checked with high power led flash light that I always use to check for back light, plus 0v on L8300
 
D

dukefawks

Administrator
You just said there was 5V on pins 28-30, those are connected to L8300. What is it now? 5V for a second then dropping off? Recheck
 
E

EJS

New member
Yes the 5v is only present for a few seconds, then drops to, and stays at 0v. Sorry maybe I wrote my original answer poorly.
 
D

dukefawks

Administrator
So the LCD is not recognized then. I assume you did a PRAM reset to be sure?

Check continuity for all connector pins to the end of a separate LCD cable to check if connector is ok. Also inspect for knocked off parts around LCD connector on top and bottom of board. This problem does usually not "just" happen...

Are you absolutely 100% sure you have a known good 2015 model assembly nothing else works properly.
 
E

EJS

New member
P RAM reset was tried a few times. I no missing components as far as I can see, and I'm definitely testing with a 2015 LCD. Will a cable from a 2012 retina machine work for testing?
 
E

EJS

New member
Diode mode measurements for the following
C8320 Pin 1 .287v Pin 2 OL
L8300 .530v
C8311 .530v
I have continuity starting at both connector side and cable side. Also reflowed all connector pins to make sure I didn't have cold joint, no change.
 
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