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820-00928-A No display on internal (works external)

ALB-Repairs

ALB-Repairs

Member
I have an 820-00928 board with no display and no backlight on the internal after liquid damage. The internal display does not show up in osx.
Tested with known good screen and cable

Has PP3V3_S0SW_LCD
BUF_EDP_PANEL_PWR_EN
PP5V_S0SW_LCD
I2C_BKLT_SDA
I2C_BKLT_SCL
after checking the LCD connector against a known good board with diode mode i found Issues linked to u9850
EDP_AUXCH_C_N OL
EDP_AUXCH_C_P OL

I replaced the U9850 Mux with one from a donor 3787 (isnt a programmed chip i dont think, so it shouldnt make a difference) and the diode mode readings are now okay on those two lines.
Still no internal display,

All other diode mode readings seem pretty perfect on on the LVDS connector now.
Im struggling to figure out why it wont recognise the internal display. Any help would be awesome!
 
Last edited:
D

dukefawks

Administrator
Check diode mode readings again on both AUX pins. Inspect the LCD cable closely as many times it has burned between the backlight pin and AUX pin. This will also have destroyed the connector on the board or LCD.

Did you use a CBTL type MUX? On some 3787 board alternate part numbers were used and they may not work. Make sure it says 6142 on the MUX.
 
ALB-Repairs

ALB-Repairs

Member
Also now replaced u9800 (from scrap board)
No change, still no internal display in OS.

Starting to go a bit loopy on this board.

PP5V_S0_SW_LCD = 5v
PP3v3_S0_SW_LCD = 3v3
BUF_EDP_PANEL_PWR_EN = 3v3

Im starting to wonder if the SMBUS lines have a problem. Anyone have any ideas?
 
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