Revamped version of the iPhone 3G with faster processing speeds. Repair of this device is similar to the 3G, and requires simple screwdrivers and prying tools. Model A1303 / 16 or 32 GB capacity / black or white plastic back.

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Pinpointing back light problem

Back light is out on my 3gs. I can see it with a flashlight. I took it apart and hooked the LCD assembly to another 3gs and no back light. obviously somthing wrong there.

But Then

I took a good LCD assemble, hooked it to the phone and no light.

Do i Have Two Problems?

Answered! View the answer I have this problem too

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it could be a short on the LCD connector and you've just blown another screen :-( if you put the good screen back on the good motherboard what happens?

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Okay, so you for sure have one phone where the backlight is working and the screen lights up, correct. You disassembled that one and replace that LCD with the one from the phone where the backlight is not working and have the same result. Now I get confused when you said you "took a good LCD assemble, hooked it to the phone and no light." Which phone did you hook it up to? The one that was working before, or the one that did not work? Sorry, I may make it sound more confusing than it really is....

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Oh, I have the same :|

The lcd assembly was wrong, and the + and - of backlite leds was shorted a few times if I pressed a top right corner of the screen. After a lock/unlock the backlite returned to life, but once again it didn't. I swaped the screen, but that does not work too. No backlite, and I have no idea how to fix it, it's mainboard problem now :|

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Deck the Halls
With tools and Fix Kits

4 Answers

Chosen Solution

"3GS Backlight Circuit

Don't be surprised if just changing the 6R8 inductor (coil) doesn't repair the backlight fault.

The 109B MOSFET + schottky diode is part of the boost converter that, in combination with the 6R8 inductor (coil), boosts the voltage to a high level to run the 6 LEDs mounted in the screen. And the boost converter itself is managed by the 338S0768 power management IC. So, any of these parts can be responsible for the backlight not functioning.

Another fault common with the 3GS is that the copper tracks connecting the output of the boost converter IC (109B) to the LCD connector can become open-circuit. There is also an independent track from the 338S0768 PMIC to the LCD connector which is involved in backlight control, and this should be checked with a multimeter for continuity as well.

And, of course, the screen itself may be faulty."

Found this Tibbit on the Web.

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great research..really clear answer, whilst 6r8 has worked in the past I've also had to do a jump wire from 6r8 directly to pin on LCD.. google it and you'll find all sorts of youtube and other repair guides that explain better than I can.

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I specifically buy 3gs iphones with DIM screens (no backlite) to repair.

In my opinion, here are the most common causes:

1. Corrosion at #1 LCD connector on board and/or LCD

2. Bad LCD

3. 6R8 coil & chip/curcuit problem

The quickest test of backlite curcuit is:

Power on phone, remove screen, and do lite test at pin 3 of #1 LCD connector on board. If there is power...backlite curcuit is probably not broken. If not, troubleshoot backlite curcuit.

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Hi Can you tell me what the reading should read please

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you guys sure do know your bread an butter... I'm interested to find out how exactly to do the said lite test at pin 3 of #1

do I need expensive equipment?

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Dear Brad!

Please help me about my problem, what's maybe just partially bit offtopic, because I have a Lenovo phone, not an iPhone. I searching

internet wide, as my skills and time let me do. This community are the closest. So, there

is my situation:

I have a Lenovo a760 Ideaphone. After one week usage display begin to vibrating, similar

to a lighttube goes to die. And the screen's border lighter, and inside a big dark spot.

And all screens transparent, so i can see on actual screen the before screen's shapes.

Now i seen on my homepage, and i can see my before used browser window's shape. I

hoped before I founded the community, this just a contact issue between the display, and

the panel. Im in Hungary (No support for IdeaPhone). Some suggestion from you?

Below image from boot screen. Normally all of screen must be black, excluded Lenovo logo, and slogan. All others seen is are remaining from the earlier session.

https://lh5.googleusercontent.com/F4ljJc...

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scott will be eternally grateful.
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