820-00165 backlight issue

[laptopcity]

Hi ive got an 820-00165 with a backlight issue, the problem is backlight does come on for a sec then goes off , it did have a liquid pill but only very light, ive change led driver just incase and c7796, c7797, c7799 just to be sure , i am getting 8.5v at L7701 so voltage is getting there

 

[2informaticos]

Maybe bad solders at U7701.
So many threads about backlight problems at 00165.
You should already got lot of info about what to check there.

Why don't you post relevant measures on the backlight circuit?

 

[JohnB8812]

Sounds like an SMC_LID problem. Tried new DC-in board/cable? J9500 pins ok?

 

[laptopcity]

Hi john , think you could be right , i didnt mention it because i didnt think it was relevent but although the board powers on and to the user logon screen all be it without backlight but it also has no green or orange charge light , thought this would be a simple fix after getting the display right , but you mention j9500 which could tie into having no charge light but the connector looks spotless, ive measured at pin 1 of j4800 keyboard connector and get between 0.7v and 0.9v, what should i see there ?

 

[laptopcity]

ok thats me being stupiud, i take it i should see around 3v but i get between .7 and .9v , doide readinmg is .502 so i dont think its a short, it looks like smc_lid comes from the smc ??

 

[2informaticos]

SMC_LID is controlled from LIO board.
Disconnect LIO flex.
If goes high, then bad LIO board, or flex; backlight should come on also.
If not, then check R5171.

Missing Magsafe light points to LIO board issue (or flex).
Usually bad connection for 3V42 between MLB and LIO board.

 

[laptopcity]

thanks to you both, although lio connector looked good, i removed it to find a bad 3v42 trace underneath, fixed the trace and replaced the connector and now green light plus backlight both working , guess thats a lesson learnt and thats fix green light issue first before anything else