Released on September 19, 2014, this 4.7" screen iPhone is the smaller version of the iPhone 6 Plus.

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No image on lcd after touch IC replacement

I have a customers iPhone 6 that had touch issues. The problem was not the screen but was on the motherboard. I changed touch IC U2402 and after process finish the lcd shows no image. ITunes recognize the phone, I can handle the phone through my pc, I can make a back up etch. But I don't know what I did wrong and I can't see the lcd image. Backlight coil is from the other side I don't think this is the problem. Can someone help me where to look on motherboard; thank you

Answered! View the answer I have this problem too

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I would also suspect the backlight circuit (just shine a torch on the display and check if you can see the lcd image) . As already stated, when applying heat to a board where the components are so close together, the chance of disturbing an unwanted component is extremely high and there is an equally high chance of effecting the backlight circuit. When soldering Smd parts, I always use captan tape surrounding the component in question to reduce the chance of heat spreading to unwanted areas.

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I think the problem is the backlight driver. This chip is exactly from the other side of the board where i heated. I cleaned the glue around the chip and removed from his place. I will order a new chip and when i will install it I will post the result

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Hi John. That is exactly your problem. Opposite the Touch IC's, on the front side of the pcb, is the backlight circuit. When you apply too much heat, you can either damage the backlight circuit or cause some loose solder joints.

You also have to be careful because the CPU is right there as well. Being stuck in place with underfill, there is always a risk that too much heat can cause the solder balls to expand and they have nowhere to go other than short each other or get exploded out from underneath.

Remove the shield over the CPU and inspect carefully for excess solder balls. Then inspect and probe the backlight circuit. You may have loose components or a defective backlight filter.

EDIT (2017/02/17)

Here are some snippets from the schematic. I would check the backlight circuit, specifically the diode, the decoupling capacitors and the ferrite beads (filters or some say fuses) on the anode and cathode side.

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Thank you for your time, I remover the cpu shield and I don't see any solder balls, I suppose the broiler is the backlight circuit. Can you help me how how to check all the components of the backlight circuit. How can I know which component failed; how to test backlight coil;

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Hi John, see my edits in my answer.

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Thank you so much. So you think the problem is on the backlight circuit?

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johnfl21 will be eternally grateful.
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