820-2936 no Backlight

[Gustavo Gomes]

820-2936 board severe liquid damaged!

Missing tracks from LCDBKL_DISABLE

Had to drill a hole on the board cause PPBUS_SW_LCDBKL_PWR was also missing

BKL_EN 2.89v
PPBUS_SW_LCDBKL_PWR 12.45v

Still no backlight!

Replace U9701?

 

[aprendiz]

Check continuity on feedback line from ball A5 to D9701...

 

[Gustavo Gomes]

continuity OK from a5 to pin2 on D9701

 

[Gustavo Gomes]

FB line seems ok, I'll try to replace U9701

 

[dukefawks]

LCD_BKLT_PWM present? PRAM reset done? Got image without backlight?

 

[Gustavo Gomes]

LCD_BKLT_PWM not present, tested without lcd.
With LCD image present.

 

[dukefawks]

LP8550 replaced and all resistors around it ok? LCD must be connected when measuring voltages. What is exact voltage on PWM?

 

[Gustavo Gomes]

Replace L8550 again, now get backlight, chime, but no image! tried different LCDS panels

 

[aprendiz]

You mean only white screen???

 

[Gustavo Gomes]

yes white screen, no image, connected HDD and USB system and nothing shows on screen

 

[Gustavo Gomes]

also reseted PRAM with USB keyboard and even if i wait long it wont show question mark or boot into OS

 

[Gustavo Gomes]

also just white screen on external monitor

 

[aprendiz]

Voltage on L9008??

 

[Gustavo Gomes]

it reads 3.22v

 

[aprendiz]

Voltage on pins 2,4,6 and 7 from J9000

 

[dukefawks]

"Voltage on pins 2,4,6 and 7 from J9000" There is 3V on L9008 so LCD is recognized.

Hanging on a grey screen like that could be anything. Disconnected everything and connect a known good LCD, see if question mark comes.

 

[Gustavo Gomes]

2 - 3,18v
4 - 3,22v
6 - 3,21v
7 - 3,21v

when doing the measures, questiom mark appeared, next reboot, didnt show again

 

[Gustavo Gomes]

replaced u9000 and comonents on pin 2 line, its working! doing further tests!

Tks!