820-00138-A Image but no backlight

[crea2k3]

Iv got an 820-00138-A in for repair, it has image but no backlight. Have tried another screen but still nothing. Its a difficult one as no boardview for it, so a nightmare to try and work out what is what. I have made the following diode readings, but don't have another board to compare it to so not overly sure what is correct and what isnt. I can see there are a couple of OL's in there. Im not sure if they should be or not, as the boardview that is marked as the 820-00138-A doesnt actually resemble the 820-00138-A .

v noticed pin 3 of q7706 is OL, its LCDBKLT_EN_L . I have tried it pos to ground and neg to ground in diode mode, and both show OL. Not sure if this is correct or not ?

PPVOUT_S0_LCDBKLT at the connector is 0.00 at the fuse its 12.55

If I check continuity between the connector pin and the diode / caps its showing as 000.3 so it appears to be connected ok to the connector.

PPBUS_SW_LCDBKLT_PWR @ q7706 = 12.55v
LCDBKLT_EN_L @ q7706 = 12.44v
PPVOUT_S0_LCDBKLT @ connector = 0.00v
PPBUS_S0_LCDBKLT_PWR_SW = 0.15v
BKLT_EN_R = 3.3v

 

[2informaticos]

Diode mode to ground at PPVOUT_S0_LCDBKLT?
Always check with red probe at ground.

Be sure D7701 is not shorted A-K.
Post voltage for U7701, pins 5, 18, 11, 17, 15, 16.
Check all the traces to J8300.

Did you test with correct screen for this model?
Try PRAM reset few times...

 

[crea2k3]

Diode mode at the connector shows OL with red to ground and also black to ground in diode mode. if I go from the connector pin back to the output caps it shows as 0.00 so has continuity.
D7701 shows 0.317 one way, OL the other way.
u7701 -
5 = 5.03v
18 = 5.03v
11 = 12.36v
17 = 3.306v
15 = 5.02v
16 = 5.02
il check the traces in a second. Iv tried smc and pram reset, wont work with any screens iv tried, just image and no bl.

 

[2informaticos]

Try another U7701.
Compare diode mode to ground on pins 15/16.
Check all resistors around it and also traces and solders.

Do you get image for sure, only missing backlight?
If possible, check with o-scope LCD_BKLT_PWM_R and I2C_BKLT_SDA/SCL.
Should catch some activity pressing backlight adjust keys...

 

[JohnB8812]

You must use a 2015 15" display otherwise you are wasting time.