(347) 552-2258 [email protected]

3787 No KB backlight

G

grmacs

Member
Everything else works. LCD backlight responds to light/dark on webcam so ALS is working. I have 5V both sides of D7720 / L7220. 5V at J4915. Tested FB lines for continuity back to resistors near U7701. Those resistors are zero ohms. R7747 measures ok. Tried forcing 3V to C7747 with R7747 removed. Replaced U7701. tested with new kb Backlight and 2 other used ones. Nothing. I'm lost.
 
2informaticos

2informaticos

Administrator
Staff member
"Tried forcing 3V to C7747 with R7747 removed."
Still 5V output then?

Be sure R7741 is good and change L7720.
 
G

grmacs

Member
YEs still 5V. R7741 is reading good. Changed L7720. Still no kb backlight with jumper or with R7747 back in place and jumper removed.
 
G

grmacs

Member
Just tried that. No change. I checked diode readings on J4915 and U7701 also. I really don't understand what is preventing the KB backlight from working... Where does the ALS actually control the KB backlight at? I'm thinking the issue must be where those two things tie together?
 
2informaticos

2informaticos

Administrator
Staff member
ALS reaction comes through SCL/SDA lines to U7701.
The information arrive to U7701, if it adjust LCD backlight.

Check all solders and traces related with keyboard backlight.
Still 5V output disconnecting webcam?

BTW, I hope you've measured all with keyboard backlight connected.
 
G

grmacs

Member
Not understanding why the hell this kB backlight won't come on. tested connections. from J4915 to U7701 and components in between. replaced all of the Caps C7723/4/5/6/7. Is there a good way to just have the kB backlight stay on? I guess I could try replacing U7701 again... I'm at a loss as to what could possibly still be wrong.
 
G

grmacs

Member
Yes. This actually had two issues when I received it, Cracked LCD and no KB backlight so the problem has persisted after swapping to another screen
 
G

grmacs

Member
I'm wondering if whatever issue this has/had could be breaking the KB backlights I"m testing? Just wondering if the amperage couldve been high at some point. I connected an LED after wondering this and I do see life in that but it comes on just briefly and then goes out til I reconnect it.
 
You must log in or register to reply here.
Top