New iPad (3rd gen) weird backlight problem

[noobfix]

Originally Posted by fs2787

The diode I got 4.1v on one leg and the other leg 3.7v
The filter I got around 3.4v on both legs.

your diode is short. I would change the filter just incase.

[Wites OM Tesla]

Originally Posted by noobfix

your diode is short. I would change the filter just incase.

Yes i agree i would replace both voltage is low.

[fs2787]

Thanks Wites, I will replace the diode and filter.

[fs2787]

I have replaced the blacklight diode and the filter. Now the blacklight diode have 3.95v on both leg and the filter have continuity and 3.95v on both leg also. Still no backlight.

Wites said I need to have 4.7v. on both leg, but I only have 3.95v. Could this be the problem. The only thing I haven't changed is the 4r7 coil. I don't think the coil is bad since it have continuity. What else could be wrong?

[noobfix]

Originally Posted by fs2787

I have replaced the blacklight diode and the filter. Now the blacklight diode have 3.95v on both leg and the filter have continuity and 3.95v on both leg also. Still no backlight.

Wites said I need to have 4.7v. on both leg, but I only have 3.95v. Could this be the problem. The only thing I haven't changed is the 4r7 coil. I don't think the coil is bad since it have continuity. What else could be wrong?

a coil can be bad with continuity. think about it coil means looped wires any open in the loops you lose the inductance, but since the open wire is rust and link altogether you still have continuity without inductance.

same logic that's why you can just jump a coil. must replace and get the inductance going. continuity means very little in this case.

[fs2787]

Originally Posted by noobfix

a coil can be bad with continuity. think about it coil means looped wires any open in the loops you lose the inductance, but since the open wire is rust and link altogether you still have continuity without inductance.

same logic that's why you can just jump a coil. must replace and get the inductance going. continuity means very little in this case.

You must be right. Using a hot tweezers, I removed both the diode and the filter and soldered the new ones on. I turned on my iPad, still no backlight. I then tried to remove the 4r7 coil using the hot tweezers, but I was not able to do it. After taken the hot tweezers away from the coil I turned on my iPad and the backlight works, but it only lasted for about 30 seconds and no backlight again. I guess the heat got something to do with it. I will use hot air to remove the coil and order some soldering paste to solder the new coil, and let see if it works.

[Wites OM Tesla]

Originally Posted by fs2787

You must be right. Using a hot tweezers, I removed both the diode and the filter and soldered the new ones on. I turned on my iPad, still no backlight. I then tried to remove the 4r7 coil using the hot tweezers, but I was not able to do it. After taken the hot tweezers away from the coil I turned on my iPad and the backlight works, but it only lasted for about 30 seconds and no backlight again. I guess the heat got something to do with it. I will use hot air to remove the coil and order some soldering paste to solder the new coil, and let see if it works.

Wait friend what kind of hot tweezers?Use soldering iron there is possible crack in solder at light coil resolder it with flux.

[fs2787]

Originally Posted by Wites

Wait friend what kind of hot tweezers?Use soldering iron there is possible crack in solder at light coil resolder it with flux.

I use a hot tweezers to remove the diode and filter, but I used a soldering iron to solder the the new diode and filter. I carefully checked the diode and filter solder joints under 30x power magnifier loupe and were not able to detect any cracks. The joints were solid and clean. What I don't understand was how come I have 3.95v on both legs instead of 4.7v?

[Wites OM Tesla]

Originally Posted by fs2787

I use a hot tweezers to remove the diode and filter, but I used a soldering iron to solder the the new diode and filter. I carefully checked the diode and filter solder joints under 30x power magnifier loupe and were not able to detect any cracks. The joints were solid and clean. What I don't understand was how come I have 3.95v on both legs instead of 4.7v?

Light Coil friend replace and i think problem will solve because voltage come through coil then in combination with PMIC it is rising more to 17V when lcd connected and light working,without lcd it must be 4.7V replace coil friend.

[fs2787]

Originally Posted by Wites

Light Coil friend replace and i think problem will solve because voltage come through coil then in combination with PMIC it is rising more to 17V when lcd connected and light working,without lcd it must be 4.7V replace coil friend.

I replaced the 4r7 coil, still no backlight . Now the voltage shows 4.15v instead of 4.95v. What else could be wrong? I was wondering if there is a cold solder joint somewhere. Should I go ahead and reflow the logic board?

[Wites OM Tesla]

Originally Posted by fs2787

I replaced the 4r7 coil, still no backlight . Now the voltage shows 4.15v instead of 4.95v. What else could be wrong? I was wondering if there is a cold solder joint somewhere. Should I go ahead and reflow the logic board?

This is what i not like to guide customers.
No friend no reheat in my hardware solution first step is connector an resolder 2 yellow marked pins,this solution is if you try other lcd with flex.

[fs2787]

Originally Posted by Wites

This is what i not like to guide customers.
No friend no reheat in my hardware solution first step is connector an resolder 2 yellow marked pins,this solution is if you try other lcd with flex.

I am not sure if I understood your answer. Do you mean try using another flex cable and another LCD screen, if this doesn’t work make a jump from the filter to one of the pin on the LCD connector like in the picture above.

[noobfix]

Originally Posted by fs2787

I am not sure if I understood your answer. Do you mean try using another flex cable and another LCD screen, if this doesn’t work make a jump from the filter to one of the pin on the LCD connector like in the picture above.

which side did you change the backlight chip its a diode it does have polarity the lines side have to point down. and are you sure the soldering with the filter is successful?

[fs2787]

Originally Posted by noobfix

which side did you change the backlight chip its a diode it does have polarity the lines side have to point down. and are you sure the soldering with the filter is successful?

Yes, I make sure the polarity on the diode is correct. Solder the filter was relatively a simple task under 5x magnification. Like I said before I examined both the diode and filter under 30x magnification and both are clean and solid. The only thing I haven't done is replacing the flex LCD cable. I knew for sure that the diode was bad, but I think the filter and coil were good. I went ahead and replaced all of them to be sure since I bought the complete backlight replacement kit. Still no backlight!

[Wites OM Tesla]

Originally Posted by fs2787

Yes, I make sure the polarity on the diode is correct. Solder the filter was relatively a simple task under 5x magnification. Like I said before I examined both the diode and filter under 30x magnification and both are clean and solid. The only thing I haven't done is replacing the flex LCD cable. I knew for sure that the diode was bad, but I think the filter and coil were good. I went ahead and replaced all of them to be sure since I bought the complete backlight replacement kit. Still no backlight!

Solution in picture is to be done after check with other working lcd then you check connectors then components.
ok friend next step but i would do this first resolder connectors not only on board but on lcd itself if still same try other lcd for test only.