820-3330 no lcd

[Melamanti]

Hey guys,

Recently a customer brought in a 820-3330 board with a getting stuck periodically problem, after some cleaning around the ram slots and the ram themselves the machine worked properly for a couple of months and then was brought back with another issue. It had no image on the lcd. Works fine with an external monitor, charges, chimes etc.

While doing some measurements around the lcd connector area, i found out that lcd_pwr_en is missing (?). I replaced u9000 still no change.
U9600 is supposed to be the ic generating that voltage right?
Am i just supposed to change that off a donor board or is there something else i should check first?
Already tried a different screen assembly.

 

[2informaticos]

Post voltage for pins 4, 6, 7 of J9000.
Check trraces/solders at J9000 and connector itself.
Be sure L9010/11 are OK.

 

[Melamanti]

L9010/9011 are fine, traces seem ok under the microscope,

Pin 4 - 3.3v
Pin 6 - 3.3v
Pin 7 - 0.082v

 

[2informaticos]

Resistance to ground pins 6 & 7; diode mode, red probe to ground.

 

[Melamanti]

Pin 6 - 0.52v
Pin 7 - 0.51v
Same measurements with lcd connected and disconnected.

 

[2informaticos]

Check R9010...

 

[Melamanti]

I have done that already, its 100k?hm as its supposed to be according to the schematics.

 

[2informaticos]

Measuring R9010/11 onboard, you must get similar reading.
Check integrity of LVDS_DDC_DATA trace.

 

[Melamanti]

Ok i got something, i got some flux on the lvds connector, did some cold joints, now i got 3.3v on pin 7.
But still no image, pins 38-39-40 of j9000 got 0v. fuse seems fine , led drive on the other hand not so well, should just change all of that just in case?
Would really love to get something out of this though.
Knowledge wise ofc, because if i do change all of it i wont have the information needed.

 

[2informaticos]

Any voltage at pins 2/3?
LCD must be connected.

 

[Melamanti]

Pin 2 - 0v
Pin 3 - 3.26v
Pin 1 of C9002 - 0v
Pin 2 of L9000 - 0v.

Lcd connected.

 

[2informaticos]

I think is better to change the LCD connector.
After removed, check all the traces, before soldering new one.
Pins 2 & 3 should have same voltage; both are tied together, as per schematic.
And if you get 3V there, image must be present; and LCD_PWR_EN too.
In such case, you must repair backlight circuit only.

 

[Melamanti]

Update, i changed the lcd connector still the same issue.
I even shorted the 2nd and 3d pins and the 2nd one still doesnt have 3.3v.
I m running out of ideas..
Is there any way this is a gpu issue?

 

[Melamanti]

The strange thing is that pin 3 has 3.3v but L9000 has no voltage, c9002 nothing as well, traces from pin 2-3 to those are fine and they have continuity. I m getting the urge to send this in the garbage pile but this was brought on some sort of "warranty". Any ideas are welcome.

 

[2informaticos]

Shouldn't be GPU issue, as external monitor is always driven by GPU.

"I even shorted the 2nd and 3d pins and the 2nd one still doesnt have 3.3v."
You did something wrong.
If both pins are tied together, cannot get different voltage.
Use boardview and identify the pins correctly.

 

[Melamanti]

That was my problem as well, but after some close inspection on the board, i found out that L8608 was missing, i put one there from a donor board and the machine booted up and is working properly.
So it wasnt a matter of lcd connector, or doing something wrong. The voltages were the ones i described even though it made absolutely no sense. Anyhow, we can count this one as solved and hopefully it will help someone with the same issue. That L8606 is right in the middle of the board and apparently if you are not the one disassembling the machine, things can get knocked off.
Thank you for all your help.