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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Most likely cause of iPhone backlight malfunction?

My phone is pretty old now and so naturally it is not without its flaws. The vibrate had stopped working and the power button was nigh on impossible to depress. When I opened it up to repair these issues I seem to have inadvertently caused the backlight to die.

As it turns out, that blob of glue in the top left hand corner had come loose and was no longer holding apart the headphone jack and volume ribbons. Ironically a screw which had come loose from the board had taken its place and prevented a short. Hence when I returned this screw to its rightful place and put the phone back together... it failed to turn on and simply got very hot, very quickly.

This happened twice before I identified the culprit and patched it with insulation tape. I was quick to open up the phone and make sure it was disconnected fast to avoid too much damage from the short. However now it appears my backlight will not function. All else is working fine however. I have taken a look at the 6r8 coil responsible for the light circuit but see no signs of damage. I am unclear however as to whether this ever looks damaged or burnt out from the outside.

It is also possible that the short simply stopped because the coil burnt out and my solution was coincidental. There is an issue with the top two pins on the top row of the LCD ribbon house also being slightly out of line. It has been like this for two years however and caused no problems.

My questions are therefore:

Does the 6r8 coil look damaged when it is... damaged?

Is running the phone without the backlight likely to cause further issues (if the coil has blown)?

What other issues could cause this?

Thanks.

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Marmaduke John, most likely cause will be a depends:-) Remember that the backlight is in your LCD. So it could be the LCD itself, check the ribbon cable, make sure there are no tears on there. Yes, a bad connector not making proper contact, can cause this as well. Next would be the backlight coil. It does not have to look damaged to be damaged. You would most likely had a catastrophic failure, (mostly power related) if it would look damaged. You can check the coil with a ohm meter. If the coil checks out okay, then the next part is the IC 109B, which is the backlight IC. That would mean either a reflow, or a reball to replace the IC. Having no backlight, due to a bad coil or IC, should not cause you any long term damage.Hope this helps, good luck.

==UPDATE==

I attached the schematic for the LCD connector as well as the backlight circuit, this way you could check the coil as well as the connector

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Sorry. I wrote a really long reply without realising this website removes all formatting and has a character count on comments.

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Thanks. I may try replacing the chip and the coil. They are the cheapest (if most fiddly) components involved. However I kind of think if either overheating or shorting was the cause then more components would likely be damaged besides. I’ve tested everything else and it all works. The coil claims to be high temperature resistant and I didn’t allow the overheat to get any hotter than I have naturally felt the phone after extended usage.

The LCD ribbon is a tad dodgy since a problem a couple years back damaged the receiver on the board (only the plastic clips though). However without knowing which pins are for LCD power and which are for LED I cannot really work out if this is the issue. Or indeed if the power is simply shared between the two without separate pins for each. There are no dead spots on the screen so the display portion of the ribbon would appear to be fully intact.

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How can I go about testing the ribbon and do you know which pins provide power to the LEDs? I have not yet taken apart the screen unit so is there feasibly any issues which could have occurred in there from this problem?

I have heard that a cause for this problem can be disconnecting the screen without turning the phone off. I had no choice but to do this after reconnecting things and temporarily losing the digitizer and being unable to press my faulty power button (phone is jailbroken so I can switch off without the button... if the screen works).

I am unclear however as to which component specifically this is likely to damage. The screen had been disconnected like this several times before without ill effect anyway... on the last occasion in which I had to make repairs and replacements.

I do not have an ohm meter but I guess I can crudely test the chip and coil with just an LED and power supply... provided I only give it what it can handle. I’ll have to look up what they run at.

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Check pin 3 of the connector with a test light. You should have power on there. If you do most likely your backlight circuitry is ok.

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Thanks for your continued assistance on this. Apologies for my very vague knowledge on the subject... my secondary school electronics teacher was punched in the face... through a window... by a student... and hence quit. Strange story but there we go.

I am assuming the first diagram there is for the ribbon connector labelled 1, which is aligned horizontally on the board. This appears to have fourteen pins each side so I assume that the topmost and bottommost are merely for the connector itself and should be omitted on the count? I guess these are the terminals labelled 25-28.

Could I simply touch an LED or bulb to this to test then? Pin 3 for the positive leg and which other pin? Apologies again but the unfortunate punching incident means this stuff is quite beyond me.

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