820-3332 no display/no backlight

[MegaObi]

no external (off hdmi)
i tried good known lcd.
Chime is present - both speakers are distorted!

 

[JohnB8812]

Resoldered U8900?

 

[MegaObi]

yes now i have image but still no backlight. i got two of these boards on my desk with same issue - hopefully when i solve one it will also fix the other. 12.6v on pin 1 on j9000.

 

[2informaticos]

"12.6v on pin 1 on j9000."
So you have LCD_BKLT_EN and of course BKLT_EN too.
Do you get LVDS_BKL_PWM_RC?

If not, do PRAM reset few times.
If still no result, remove R9704 and run a wire from LVDS_BKL_PWM_RC to BKLT_EN.
If works, do PRAM reset again.
Resolder all components (remove the previous wire),test and comment...

Consider to remove EFI password, if is the case.

 

[MegaObi]

3.3v on lcd_bklt_en 3.1 on bklt_en
lvds_bkl_pwm_rc is missing/very low ~100mv

i remove r9704 and run jumper from bklt_en to lvd_bkl_pwm_rc still no back light.

 

[2informaticos]

Check all traces and components around U9701.
Pay atention to R9708/09 and all return resistors.
Try known good LCD assembly.
Change U9701.

Do all these tests keeping 3V at LVDS_BKL_PWM_RC.

 

[MegaObi]

i changed u9701 still same i get 2.49v on lvds_bkl_pwm_rc

 

[MegaObi]

hey solved was bad u9701