Macbook Pro A1502 No Picture no Backlight

[platinumsteel]

Hi guys am working on a 820-4924 that is giving me some serious headache. I have picture on external display. But nothing on the internal. I don't have pin 1 on lvds connector PPVOUT_S0_LCDBKLT and i don't have pins 28,29,30 . I have voltages 5v on U7700 pins 5 ,18 , But i am missing pins 17 which should be the enable pin. Can you all please guide me further on what to check? I also replaced U7700 from a donor board and nothing changed. Can you guys tell me if maybe U7700 is dead ?

[piernov]

Re: Macbook Pro A1502 No Picture no Backlight

Image present on internal display?
PRAM reset done?
Known good 2015 (not 2013) LCD assembly?

[platinumsteel]

Re: Macbook Pro A1502 No Picture no Backlight

Well to be honest this is indeed the original screen for it.It was working before but the original board had a blown PCH so they ordered a used replacement board and now this issue.Shows no image and no backlight on the internal screen but image on external.No apparent signs of damage under my microscope to the lvds or all the rails associated with lcd and backlight.I will be getting a working identical 2015 MBP to test in 1 week or so.It's just i wanted to rule out everything else in the meantime. I have not done a pram reset.I will try it now and see how that goes thanks.

[mon2]

Re: Macbook Pro A1502 No Picture no Backlight

Hi.

1) Please see and post the voltage values for the attached locations.

2) power down and remove battery. Meter in resistance mode (200 ohms).

Red probe on PPVOUT_S0_LCDBKLT.

Black probe on ground.

What is the resistance reading on PPVOUT_S0_LCDBKLT rail ?

[platinumsteel]

Re: Macbook Pro A1502 No Picture no Backlight

PPVOUT_S0_LCDBKLT diode mode measures and starts off at 2.544M and kinda rapidly drops down to 0.565M and kinda fluctuates.
I have attached the voltages that you requested below

[mon2]

Re: Macbook Pro A1502 No Picture no Backlight

New requests.

Voltage readings for each ?

[platinumsteel]

Re: Macbook Pro A1502 No Picture no Backlight

Voltage readings of new request

[mon2]

Re: Macbook Pro A1502 No Picture no Backlight

The left side panel enable signals come from the PCH. That is out of my comfort zone.

That noob kid @Piernov knows something about that area.

Curious to learn more about this case. Could it be a lid sensor fault?

[platinumsteel]

Re: Macbook Pro A1502 No Picture no Backlight

Okay so this is something i am now noticing.on U8330 pins 6 and pin 3 .. as soon as i plug in the charger and the macbook starts up 3.3v appear on those pins and stays for 5 seconds then disappear forever.Same thing on U8300 pins 2..3.3v just comes for 5 seconds and goes.Not sure if that means anything.Also i measured R5250 and i got 3.3v there. so it does not think it's Lid is closed I presume.

[mon2]

Re: Macbook Pro A1502 No Picture no Backlight

Meter in resistance mode (200 ohms),

Red meter lead on L8300, pin # 2 = PP5VR3V3_SW_LCD.

Black meter lead to ground.

What is the resistance to ground reading of the PP5VR3V3_SW_LCD rail ?

[platinumsteel]

Re: Macbook Pro A1502 No Picture no Backlight

1.945M and it keeps rising.PP5VR3V3_SW_LCD

3.455M and rising. PP5VR3V3_SW_LCD rail

[mon2]

Re: Macbook Pro A1502 No Picture no Backlight

What is the voltage on L8300, pin # 2 = PP5VR3V3_SW_LCD during the first 5 seconds when you see U8300 pins 2 @ 3.3v ?

I believe U8300 is a delayed load-switch.

Does this rail also go to +3v3 for 5 seconds and then off ?

[platinumsteel]

Re: Macbook Pro A1502 No Picture no Backlight

Well only with the screen removed .It goes to 0.45V for 5 seconds then gone on Pin 2.

[mon2]

Re: Macbook Pro A1502 No Picture no Backlight

To clarify, your latest resistance readings were taken with the lcd attached?

The voltage is 0.45v with the lcd display attached?

[platinumsteel]

Re: Macbook Pro A1502 No Picture no Backlight

The voltage is 0.45v with the lcd not attached.if I attach the lcd I get no readings 0v.

[mon2]

Re: Macbook Pro A1502 No Picture no Backlight

Then u8300 may be defective. This component appears to be like a solid state relay. It should pass through the input voltage but is not. Check the power rail to u8300 is there. Otherwise I think it should be replaced. After part replacement, check this rail again without the LCD attached.

[platinumsteel]

Re: Macbook Pro A1502 No Picture no Backlight

Ok so i replaced U8300 and now with the screen out it gives me 5v for 5 seconds then disappears. With the screen plugged in it does the same when i plug the charger and it chimes i get 5v for 5 seconds then gone. This board is a mystery board. I will pack it up and next week when i get the working screens and stuff i'll be able to do a proper check. I will have new U7700's coming in too. Thanks a lot for you all time mon2. I will report back as soon as i get different results.

[platinumsteel]

Re: Macbook Pro A1502 No Picture no Backlight

Okay guys I just thought i would post back since I think i now realize my problem. The issue is I do not have Pin 17 of U7700 which is the enable Pin.I believe It's is because of U8330 which generates the 3.3v for Pin 17 is not functioning properly. If you look at the picture below I don't have input voltage for U8330 and that input voltages comes from the PCH. Is their anyway I can inject and maybe provide input voltage for U8330 and do the job of the PCH?
There is no short in and around there.I had already replaced U8330 but still the same.

[mon2]

Re: Macbook Pro A1502 No Picture no Backlight

Hi. I am sure to get flamed for this but personally do not see any issues on a possible work around.

A key concern is why is the PCH is not sending the proper signal for this dual-gate OR IC to output the desired logic high "1" on pins 7 & 3 ?

From many readings, suspecting that most techs will stop the repair upon reaching a serious PCH issue due to the large # of balls on the BGA device?

We hope to get into PCH / CPU replacements in the near future but still need to make the room for our BGA rework station.

You can consider to:

1) remove U8330 off the logic board - this will then isolate the PCH signals to the LCD display connector.

2) Then locate a 3v3 rail and apply it with a small wire to the 0201 pad @ R8330, pin # 2. Do the same for R8331, pin # 2. You will leave U8330 OFF for this "hack".

So you are manually applying the logic high to enable each leg of the LCD display. The PCH will have no role in this.

Be sure that pin # 1 of each of the no-stuff resistors @ R8330 & R8331 are NOT used nor shorted to the +3v3. We DO NOT want to feed this voltage back to the PCH.

Not sure how this will turn out with respect to lid closing, etc. - it is possible that the display will now remain always on but not sure.

You can at least test the idea and post your findings. Curious to know.

PS: Is it possible that you have had liquid damage to the PCH area ?

[piernov]

Re: Macbook Pro A1502 No Picture no Backlight

If LCD is not recognized, image will not be sent to it either way.