820-00875 - Internal screen not working

Sykulski

Member
I have this one with no image or backlight on internal screen. External screen works fine.

History is customer tried to replace cracked screen (which had image and backlight but with broken LCD). He somehow replaced the screen with the power applied and now no screens are working. Also not the original broken one. Tried two new known-good ones. The original with crack also works i another machine. So logic board issue here.

If something shorted because of connecting the screen while powered on what would be the first suspects ? I cannot see or smell anything burned...

PP5V_S0SW_LCD = 0V
PP3V3_S0SW_LCD = 0V
EDP_PANEL_PWR_EN = 0V
PANEL_P5V_EN = 0V
PANEL_P3V3_EN = 0V
 
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dukefawks

Administrator
Damaged connector would be a first suspect. Next would be a diode mode test on all pins. Both screens have a LCD cable, you did not swap that over so that could be the problem?

Also inspect for damaged/knocked off components around LCD connector, easy to do with tool or nails.
 

Sykulski

Member
Connector on logic board looking perfect as well as connector on LCD board also have no visible damage. I tried already with several LCD cables. Also all components around this area are in place and with none visible damage.

I will take the diode measurements on the LCD connector but I can only do it with the LCD (cable) disconnected as the connector is put in from the top in this model. Would this be fine ?
 

Sykulski

Member
J8500 diode mode (LCD disconnected)

--- All GND-pins (2,5,8,11,12,17,18,20,22,23,29,32,35,41,42,47-68) ---

0,002

--- SIGNAL-pins ---

1: OL
3: OL

7: OL
9: OL

13: OL
15: OL

19: OL
21: OL

25: OL
27: OL

31: 0,384
33: 0,384

37: 0,384
39: 0,384

4: 0,569
6: 0,512

10: 0,505

14: 0,726
16: 0,753

24: 0,509
26: 0,509
28: 0,720
30: 0,720

34: 0,534
36: 0,541
38: 0,724
40: 0,724

--- PWR-pins ---

43: 1,171
44: 0,530
45: 0,529
46: 0,438
 

dukefawks

Administrator
That looks ok. Make sure to check all caps C8520-29 for damage. If that is ok then the sucky part of checking power to the LCD on pin 44 and 45. Check while powering on as there may only be power there for a second if no screen is recognized.
 

Sykulski

Member
The caps are looking splendid and measuring between 80-100 nF in circuit.

I get a spike once while powering on at pin 44 and 45:

Pin 44: 3.30V for 600ms
Pin 45: 5.12V for 600ms
 

dukefawks

Administrator
That is what happens if no LCD is connected. I'm still suspecting the connector, pins 1,3,4,6 are important for LCD detection. See if they have continuity to the other side of the LCD cable.

Power pins too of course 44 and 45.
 

Sykulski

Member
Pins 1,3,4,6,44,45 have continuity to the other side of the LCD cable. I measured from nearby probe points as the LCD cable connected is making it impossible to measure on the connector directly
 

dukefawks

Administrator
Pins 44,45 were measured with LCD connected if there was a pulse? Need to make sure they also have that voltage when a load is connected. This one is getting annoying. There is of course the possibility that both LCD were fucked up somehow.....
 

Sykulski

Member
Yup tell me about it...

Pins 44,45 have spike with both the screen connected and disconnected.

Both LCD are working for sure because I have another 820-00875 that they work on. I have tested with three displays (two good ones and a cracked one). All three working on good board. None working on bad board...
 

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Sykulski

Member
SMC_LID_LEFT = 3.37 V
SMC_LID_LEFT_R = 3.37 V

SMC_LID_RIGHT = 3.37 V (only with audio flex cable connected in J6600, otherwise ~10mV)
HALL_SENSOR_RIGHT = 3.40 V (only with audio flex cable connected in J6600, otherwise ~10mV)

LID_OPEN = 3.37 V
LID_OPEN_R = 3.40 V
 

dukefawks

Administrator
Kind of out of ideas right now. Experience with these is still limited of course. Got a working board to compare things with? See what happens on BUF_EDP_PANEL_PWR_EN too.
 
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