A1502 820-4924-A no image

[hgoncalves]

Hi,
I have an A1502 820-4924-A that has image on external monitor, but no image on internal LCD.
The LCD connector was a little burnt, and so i changed, but without success.

Tried with known good lcd, without success.

I have 5V on pins 28 ~ 30 of J8300
F7700 = 12.59V

I have on U5450:
PIN 3 = 8.8V
PIN 4,5 and 6 = 12,59V

LCDBKLT_EN_L = 8.8V

Can you help?

 

[2informaticos]

"I have on U5450:
PIN 3 = 8.8V"
I hope not; pay atention to schematic.

Post diode mode to ground at both pins of D7710; w/ and w/o LCD connected.

"LCDBKLT_EN_L = 8.8V"
BKLT_SD level?

 

[hgoncalves]

I didn't realize that PIN 3 of U5450 was PP3V3, but the measure is correct. It has 8.8V (measured with two different multimeters).

Diode readings D7710 :
With LCD =
PIN 1 =1.2V
PIN 2 = 0.9V

Without LCD =
PIN 1 = 1.2V
PIN 2 = 0.9V

LCDBKLT_EN_L = 8.8V (R7702)
BKLT_SD = 5.9V (R7702)

R7702 = 63.3 K ohm

 

[2informaticos]

Very strange values.

Do you really have 8.8V at 3V3_S4???
Check at U8000.

 

[hgoncalves]

Sorry..
I'm a dumm. I was measuring at the wrong component...
I don't have the U5450 on my board. I confused it with the Q7700

 

[2informaticos]

Rebuild the trace...

 

[hgoncalves]

Sorry..
I'm a dumm. I was measuring at the wrong component...
I don't have the U5450 on my board. I confused it with the Q7700

On Q7700 I have:
PIN 1 = 12.59V
PIN 2 = 12.59v
PIN 3 = 8.8v
PIN 4 = 12.59V
PIN 5 = 12.59V
PIN 6 = 12.59V

3V3_S4 is 3.3V

On U7700 I have:
PIN 17 = 5.1V
PIN 2 = 5.1V
PIN 21 = 44V
PIN 15 = 5.1V
PIN 16 = 5.1 V
PIN 8 = 5.1V

D7710:
PIN 1= 49V
PIN2 = 8.3V

 

[2informaticos]

"D7710:
PIN 1= 49V"
Backlight driver is OK; there is no connection with LEDs strip.
You have a problem with LCD connector, video cable, or display (most likely).
Correct voltage is 40V aprox; when LEDs strip is properly connected.

 

[hgoncalves]

I've tried 2 LCD's.
I've replaced the J8300, because mac had no image, and J8300 was a bit burnt on pins 28-30. With other J8300, and with other LCD, it still has no image. I'm testing it with the board alone, and a known good LCD, but still no image.
Can it be a bad solder J8300?

 

[2informaticos]

Bad solders, or bad contacts inisde connector.
Do you still have 49V after all changes?
Clean with IPA when you insert the video cable.

 

[hgoncalves]

Hi,
Sorry for the long time to answer.
I've replaced once again the J8300 connector and I still have no image, and 49V on D7710. All the solders are OK, and J8300 well cleaned with IPA.

 

[2informaticos]

Then bad video cable, or display...
Just in case, check backlight voltage on a good machine.

 

[hgoncalves]

Hi,
In a working A1502, the BL voltage is 48.8V. However, it seams that when I twist the cable, it shows a dim image, I'll try with other LCD.