Macbook Pro A1502 820-4924A no backlight

[drscoot]

I've been testing for several hours at this board, including most tips from Louis video https://www.youtube.com/watch?v=nH-mWAt0CDI
But still no luck, screen is there but no backlight. Also no fan spin, but maybe that is temp regulated? HDMI is OK.
There were some minor stainmarks around the lcd connector, but the white dot is not red.
So far I found this bizar; with only the lcd connected, on the caps in the PPVOUT_S0_LCDBKLT circuit (that goes to pin1 of lcd connector), all these caps measure short to ground on both sides! When I disconnect the lcd cable only 1 side of the caps is to ground. I check at the 2 sets of 7 large caps, like C7760, C7770...
I'm wondering if that is normal behaviour, or is there something wrong with the lcd-(cable)?
When I measure at the lcd connector on the logic board pin1 is MOhm to ground. And pin1 on the cable is only 2.5Ohm.

[mon2]

Re: Macbook Pro A1502 820-4924A no backlight

With the LCD cable removed, what is the voltage reading of PPVOUT_S0_LCDBKLT ?

If U7700 and supporting components are working correctly, this switching boost regulator should be supplying a higher voltage than its input of PPBUS_G3H. Should be 25V++.

I believe that you should see this higher voltage even without the LCD screen mated @ J8300.

Inspect the LVDS cable for any possible shorts.

[mon2]

Re: Macbook Pro A1502 820-4924A no backlight

I think the display is required to enable the backlight.

Is the LVDS cable removable on both sides of the cable?

[drscoot]

Re: Macbook Pro A1502 820-4924A no backlight

thanks for the reply,
With the lcd cable disconnected from the LB, I measure no voltage at pin 1 of J8300. I suppose the lcd needs to be connected before there is a voltage on pin 1.
btw. the bare LB draws at startup about 0,7A and after about 2min it is 0,25A
Now I have a look at the other side of the lcd cable.

[drscoot]

Re: Macbook Pro A1502 820-4924A no backlight

Well I made some progress, on the lcd side the LVDS connector was corroded.
I was able to clean both Male and Female sides, if I now measure resistance on pin1 of the cable at the LB side I have 15 Ohms instead of 2,5 Ohms. Both with lcd cable not connected to the LB. Once connected, still no BL and continues reset, I hear the bong sound every so seconds. W/O the lcd connected, normal boot.
So it looks like the cable or the lcd board has something more wrong.
I'm wondering what the normal expected ohms value is of pin1 at the LVCS cable?

[mon2]

Re: Macbook Pro A1502 820-4924A no backlight

Even @ 15 ohms, sounds low for the backlight led rail but never personally measured it.

Is this a screen where you can open up to the board (T-conn?) on the display itself?

Have seen some scary videos on the many layers of the display.

For some inspiration:

https://www.youtube.com/watch?v=1CzM0SRtX6U


https://www.youtube.com/watch?v=O2j4tDv8jRU

[Stephen]

Re: Macbook Pro A1502 820-4924A no backlight

The cable on these models is replaceable and is easy to replace. I would suggest replacing the cable. It is very common for the cable to fail in situations. Also have you checked the Backlight fuse? And also if you replace the Cable and the Backlight fuse is not blown, I am going to suggest replacing the LVDS connection because that is most likely the culprit.

[drscoot]

Re: Macbook Pro A1502 820-4924A no backlight

Well the connector was corroded at the lcd side, after cleaning the resistance changed, but still not working. After some closer looks, it seems that the outer pin (pin1) is partly missing at the cable side near the lcd.
So yes new cable on its way, hoping that the screen side connector is still OK

[Stephen]

Re: Macbook Pro A1502 820-4924A no backlight

if the screen side connector is bad it is repairable. You will have to use a Solder Flat Blade tip to remove the LVDS connector on the LCD. Do not use a heat gun or you will melt the connections and burn your LCD.

[drscoot]

Re: Macbook Pro A1502 820-4924A no backlight

I adding some microscope shots of the connector. It looks like pin1 is completely gone on the cable. Also the screen connector looks bad, not sure if that's still good to go? I think there is some melted metal behind the outer pin, that blob?
When I look at the boardview, J8300 has 43 pins, here I see 30, how?
Pin2 on the board seems desoldered, but wait boardview says it is unconnected...

[ACS-Repair]

Re: Macbook Pro A1502 820-4924A no backlight

Definitely your LVDS cable is toast. unfortunately, I suspect that the connector on the display is bad as well. The "blob" you are seeing on that connector is melted plastic coming through the back. As Stephan says, you will need to replace that screen connector.