820-2936-B, No internal display

[Anterweb]

This had liquid damage, small amount and some corrosion to J9000,

I replaced j9000, machine now starts up, fan spin, I get flashing folder when connecting external display but nothing when using internal display, tried a second know good screen to be sure,

Soldering to j9000 checked all pins solid no bridges looks good!

Any help appreciated.

 

[2informaticos]

Post voltage at pins 4, 6, 7.
Check L9008 and R9008/9.

 

[Anterweb]

pins 4, 6, 7 = all at 3.28v

L9008 looks good at 0 ohm
also R9008/9 look good both reading 2.17k


I did notice that from the boardview to my actual logic board I dont appear to have c9015 present on the board, Either it was never there or I have knocked it off without noticing until now but I cant see that that would effect anything?

 

[2informaticos]

Forget C9015, is not critical.
Do you get 3V at pins 2/3 too?

 

[Anterweb]

I traced pins 2/3 all the way back to U9000 = 0v

 

[2informaticos]

Check diode mode to ground at pins 6/7.
Just in case, check if LCD_IG_PWR_EN come high.
PCH needs good communication with LCD, before release it.

 

[Anterweb]

While checking the above I spot the giant "P" under the scope,,,,,

FFS!!!! F9700 backllight fuse!!!!!

Sure as shit its dead! replaced and it's all working perfectly!

Thank you for getting me to another fix and sorry for wasting your time on this one . I should have spotted that out of the gate!!!

Much love Inf!¬ xxx

 

[Anterweb]

Ahhh nuts!

Spent the time rebuilding this today to give it back, put the entire machine back together, one last boot to test and...

White screen.. Nothing else,

External monitor it boots perfect into os, internal display just shows a bright white screen,

Spent ages going over the board under the scope and looking at the schematic, im stumped!
What have I done

 

[2informaticos]

Missing 3V at pins 2/3 of J9000?
Check L9004 and U9000.

 

[Anterweb]

2/3 J9000 = 0v
L9004 =0v
U9000, pins 2/3 =3.3v
Pin 1 power enable= 0v
Pins 4/5 =0v

 

[2informaticos]

Really strange.
If you have backlight, PCH recognized internal LCD.
Check U9000, its solders and traces; change it even.

 

[Anterweb]

I'm away from the desk now but was just browsing older posts on this forum and found a similar thread from 2016 where it was stated that it makes a difference if the lcd ribbon connector is inserted or not. I was currently testing on the bench. Do I need to have the screen plugged in to get 3v on pins 2/3 or get power enable on U9000?

 

[2informaticos]

Of course!

 

[Anterweb]

"feel like a right nob now!"

Sorry, I thorght I was to always to take readings on the bench unless stated otherwise,

Just looking at the schematic, I have a question, can a 0 ohm resistor be replaced with a jumper wire? I can't see why not?

I really struggle replacing some of these tiny components using an iron with others in close proximity, and can't use hot air so close to the plastic of the lcd connector, do you use hot tweezers? What's the best method for replacing or swapping out these tiny smd components from the donor boards?

I find they stick to my tweezers and it's a nightmare!?

 

[2informaticos]

I use JBC hot tweezers to replace small components.
You can bypass 0 ohm resistors with tiny wires.