820-00165-A No back light

[Dewanbd]

Water damages around bcklight driver changes couple cap and reg and found
PPVOUT_SW_LCDBKLT_FB=18v and slowly drop 8.56v
BKL_EN=2.8v
BKL_PWM=0v
Remove R7704 and connect PWM directly to 3V ( C7711 ) and i see it works.
Is it the permanent fix or is there any demerits.Thanks.

 

[2informaticos]

First of all, do PRAM reset.
Is R7704 OK?

 

[JohnB8812]

This is not a fix that will keep full brightness forever, and that's not necessary on a 00165. Put R7704 back and tells us exactly what voltage you get on backlight output.

 

[Dewanbd]

After Put R7704 back
bklight output at C8317=18v and slowly drop 8.56v

 

[JohnB8812]

Did you already replace the LED driver and components near it? This sounds like an SMC_LID issue if voltage is dropping like that. Tried known good DC in board and flat cable?

 

[Dewanbd]

Yes i replace the Led driver and now i see bklight output at C8317=8.56v and i tried good known DC in board and flat cable too.

 

[2informaticos]

If you got 18V, then 8.5V after replacing U7701, I bet for bad solders.
Reflow the chip, it supports very good the heat.

 

[Dewanbd]

Before replacing U7701 i got 18V, then 8.5V . After replacing now i got 8.5v.

 

[2informaticos]

If you didn't touch anything else, should get same voltage like before.
I suppose no good solders on the chip.
Post resistance to ground on all its connections, diode mode, red probe to ground.
Use surrounding components as test points.
Let the board to cool down first.

 

[Dewanbd]

resistance to ground on all its connections, diode mode
PP3V3_S0=.315
PP5V_S0=.411
LCDBKLT_BOOST=OL
LCDBKLT_FB=.582
BKL_ISEN1=.584
BKL_ISEN3=.584
BKL_ISEN5=0L
BKL_ISEN6=OL

BKL_EN=.517
BKL_PWM=.486
BKL_SDA=.430
BKL_SCL=.430
BKL_FSET=.519
BKL_ISET=.516
BKL_FLTR=OL
BKL_VSYNC_R=OL

 

[JohnB8812]

Bad soldering on the LED driver or blown feedback/switch line from the LED driver

 

[2informaticos]

As I told you, bad solders...
All ISENx lines should have (very) similar value.
OL means ball not soldered (under U7701), or blown Isense resistor; depends which point you checked the value.

BTW, you have bad solders on other lines too, not only Isense...

 

[Dewanbd]

I reflow LED driver and now it works. You guys awesome, Thanks a lot you all.

 

[shanenin]

This is not a fix that will keep full brightness forever, and that's not necessary on a 00165. Put R7704 back and tells us exactly what voltage you get on backlight output.

why won't that keep it full brightness forever?

 

[JohnB8812]

It WILL keep it at full brightness forever which is not necessary unless it's an 820-2914/5 for a bandaid fix. His problem was bad soldering on the driver. He corrected it now it's working.

 

[Dewanbd]

JohnB8812 , you are right. Thanks.