Macbook A1502 820-3476-a no backlight

[sdogs]

Happy Sunday guys ;-)
I have a macbook pro 13 A1502 on my hands with a backlight problem.
After the measurements I noticed that PPVOUT_S0_LCDBKLT shorted to ground, in order I removed the following components:
C8300 and C8303 and always at pin 1 of both short circuit present;
D7710 short circuit present at pin 2;
R7731 and R7732 and short circuit always present;
C7713,C7714,C7715,C7716,C7717 and short circuit always present;
I also replaced the LVDS connector but the result hasn't changed, even without the connector on the logic pin 1 is shorted..... what do I do now?
I checked the schematic and it seems to me that I haven't left anything out, has anyone had problems similar to mine?

[mon2]

Re: Macbook A1502 820-3476-a no backlight

Is the short still present without the lcd connected?

[sdogs]

Re: Macbook A1502 820-3476-a no backlight

it is always present at pin 1 of the LVDS connector, even with the connector unsoldered

[mon2]

Re: Macbook A1502 820-3476-a no backlight

To confirm, your meter is auto ranging or is a manual adjust for resistance? Could the meter scale be too low for the resistance?

Goto diode mode. Short the meter probes. Should tone beep. Now check the same lcd pin #1 and other probe to ground. Still a tone beep?

[sdogs]

Re: Macbook A1502 820-3476-a no backlight

the tester is the usual one that I have always used in diode mode, always short sound and presence, the components that I replaced I first measured before removing them from the logic that I recovered for spare parts.
The strange thing is that I don't seem to see other interested parts, I also measured without soldered LVDS connector, I removed and replaced each part affected by the short, I'm probably missing something

[mon2]

Re: Macbook A1502 820-3476-a no backlight

If you lift up one leg of the diode, still a tone beep? I am stuck at a dentist office, waiting on my son so do not have the schematic access at this time. Will review it later but the suggestion is to isolate the rail where possible. Lift the one leg of the diode in case it is leaky.

[sdogs]

Re: Macbook A1502 820-3476-a no backlight

I checked and the lcd pin 1 is not shorted, measured diode mode between pin 1 and ground
all measurements made by removing the component to try to isolate the short, both the diode and all the capacitors involved

thank you, you are very kind as always, I look forward to hearing from you ;-)

[dongthoai9xvn]

Re: Macbook A1502 820-3476-a no backlight

do you replace another screen yet ?

[sdogs]

Re: Macbook A1502 820-3476-a no backlight

I don't know if the owner changed the display. personally I limited myself to doing the tests I have mentioned so far. I don't want any binary to be damaged. unfortunately even under the microscope jon I seem to see damage to the pcb

[sdogs]

Re: Macbook A1502 820-3476-a no backlight

At this point I don't know what to do, I've looked into all the possible causes....
Could injecting a voltage into the short be of any use?

[mon2]

Re: Macbook A1502 820-3476-a no backlight

Switch to resistance mode. Measure the resistance to ground of this same pin that is shorted. What is the measurement?

[sdogs]

Re: Macbook A1502 820-3476-a no backlight

seems like a never ending story ;-). update, I noticed that C3095 was heating up, measured it was shorted so I immediately replaced it. Taken by the enthusiasm I did an ignition test, smoke result from the LVDS connector at pin 1, I think this too was gone, now I will have to order a new connector for the logic and also a lvds cable, I assume that for the short circuit it is broken.
Now on LVDS pin 1 of the resistance mode connector I have about 380 ohms
is it therefore the case to order a new cable and a new LVDS connector?

[mon2]

Re: Macbook A1502 820-3476-a no backlight

That is an improvement but the resistance is still considered to be low.

Remove the display and measure again.

[sdogs]

Re: Macbook A1502 820-3476-a no backlight

the measurement carried out without the display connected and the result is what I indicated above, or 380 ohms
it seems there is still something that brings PPVOUT_S0_LCDBKLT to the ground
from the tests I carried out after replacing C3095 it seems that now, there is no image on the display, I assume that the smoke has somehow damaged the LVDS connector and cable, I am afraid that without changing these two components I cannot carry out other tests

[sdogs]

Re: Macbook A1502 820-3476-a no backlight

after several attempts and after changing a capacitor (C7713) the short circuit seems to have disappeared, now at pin 1 lvds (in diode mode) I have 0.51 ohm and 55 k ohm in resistance mode.
Probably the connector as a result of the short circuit must have gone to hell... in fact if before the intervention you could see something without backlighting now I don't even have a video signal, I assume that something related to the video signal is not working...

[sdogs]

Re: Macbook A1502 820-3476-a no backlight

That is an improvement but the resistance is still considered to be low.

Remove the display and measure again.

what do you think of the new measurements?

[mon2]

Re: Macbook A1502 820-3476-a no backlight

The new resistance looks good.

Measure, very carefully, the voltage to ground of PP5VR3V3_SW_LCD at the connector. This is the power rail to power the LCD display.

[sdogs]

Re: Macbook A1502 820-3476-a no backlight

after the measurement and I get 5.15 v for about 3-4 seconds, then it goes back to zero

[mon2]

Re: Macbook A1502 820-3476-a no backlight

So this may explain why the display is dark aside from a missing backlight. The main logic board is shutting down the power rail to the display.

The next logical step is to trace this same power rail back to the regulator linked to the display. It will feature an enable pin.

Check if the enable pin is also active for 3-4 seconds and then shutting down the power rail. If not, and the enable pin is always ON, then the local power rail regulator is defective.

Also of concern is the current draw sensor for this power rail and the backlight rail. If the current sense circuit is defective (ie. missing parts / traces) then the logic board will force the rail to shut off as it believes there is too much of a load (current draw) and is beyond the spec outlined by the design engineer. That is, like an electronic fuse.

[sdogs]

Re: Macbook A1502 820-3476-a no backlight

I know I'm stressing you, forgive me ;-) As per the attached image, do I follow the line?
The regulator is U8300 at pin 5, is this correct?