820-3115 no backlight liquid damage

[cpdist]

I got a board in that had liquid damage on the lvds connector. it was pretty bad. I pulled the connector off, cleaned the area really well. Soldered a new connector on,
As a persecution I also changed the back light fuse.

PINS 21 and 22 for the lvds connector have the solder pads missing.
I bridged the pins together and ran a jumper to C9796.

I also measured the resistance on R9715 and R9731
R9715 - 97k ohm
R9731 - 194K ohm ( which is the 301k ohm) I have changed this resistor twice now and get the same measurement.

Fuse voltage on both sides - 10.9v

I also tried a known good screen same thing, image but no backlight. Where should I go from here.

I included a picture of the jumper wire i ran for the missing solder pags on pins 21 and 22 .

 

[ALB-Repairs]

Have you confirmed this is not no backlight rather than no display?. Could you tell us the voltage on the LVDS connector itself?
Thanks

 

[cpdist]

Yes If I hold the screen at the correct angle I can see an image on the screen,

pin1 - 0
pin2 - 0
pin3 - 0
pin4 - 3.2v
pin5 - Sync .14v
pin6 - 3.2v
pin7- 3.2v

I did change c9015 and l9004 after I took these measurements and found out that im missing 3.2v on pin 2 and pin 3.
Still same readings after changing c9015 and L9004.
Thanks.

 

[ALB-Repairs]

What do pins 21 and 22 measure? lets work backwards.

 

[cpdist]

Those pins measure 0.0v
I took the measurment on the pins them selves and also on c9796 and c9020 0.0v

 

[ALB-Repairs]

Firstly why are you using a 2936 screen connector on a 820-3115? i hope youve changed the cable too.
voltage on this net? PPBUS_SW_LCDBKLT_PWR.
If 12V check R0910

 

[cpdist]

Im using this connector because its all I have at the moment the other connectors are on order. This is not a permanent solution. Can I be causing additional damage using this connector? Youll have to excuse some of my inexperience im still pretty new to logic board repair.

I measured PPBUS_SW_LCDBKLT_PWR on q9706, from what I understand I should have 12v on PIN 1,2,5,6 and all those pins measure 1.3v

Thanks for your help.

 

[ALB-Repairs]

The way this part of the circuit works is q9707 is gated on pin 2 and 5. this pulls LCDBKLT_EN_L to ground. When this is pulled to ground R9788 and R9789 create a voltage divider on LCDBKLT_EN_DIV. This gates Q9706 and allows voltage to pass.

So you need to check the gate signals of Q9707, and the voltage on LCDBKLT_EN_DIV.

IIRC theres a via that can fail somewhere around here causing the issue but you should rule out R9788 and R9789 first.

 

[cpdist]

This is where my inexperience comes in. Understand the function of what you are talking about just not sure how to apply what you have asked me to do.
How do I check the gate signals of Q9707

I measured R9788 and R9788
R9788 - pin1 = 12.5v, pin2 = 12.1v
R9789 - pin1 = 12.1v, pin2 = 12.0v

 

[ALB-Repairs]

okay we can establish the voltage is not being pulled to ground, So you need to check the voltage on pin 2 and pin 5 of q9707

 

[dukefawks]

LCD is not recognized as there is no 3V on pin 2 and 3 then the backlight will also not be enabled of course. Probably because you are using a wrong connector and not making contact.

 

[cpdist]

Q9707
pin2 = 3.3v
pin5= 0.0v

 

[ALB-Repairs]

Derp. Completely missed that. Pfft, i did ask him if hes verified an image on the screen. Witch in theory there shouldn't be if he doesnt have 3v on pin 2 and 3 like duke said.

 

[cpdist]

Okay, I should have correct connector tomorrow or Tuesday, Ill swap it out, But I undoubtedly have "ghost image" on screen I can see the apple when it posts. Its not just my subconscious putting it there

 

[dukefawks]

If you have an image then your measurements are incorrect. Pin 2 and 3 must have 3V for that to happen

 

[cpdist]

I understand that, im more convinced now that the connector is causing a problem. Which is also causing incorrect measurements. Thanks guys ill let you know the measurements after replacing the connector with the correct one.

 

[jadao]

I confirm definitely.
Last time I tried a 2936 lvds cable into a 3115 LB connector it worked at a certain point until the screen went all white and then black no more lcd. I found L9004 burned open.