I see this post is super old, but I just arrived here from randomly looking posts and wanted to share a bit, maybe someone stumbles here looking for solutions. And, as what I’m going to tell applies for many mobiles, welp! I’ll just share.
So! As much as I likes your crazy Frankenstein idea, I’ve to tell you that it falls quite fast into the crazy part only :). There are a bunch or reasons for your plan to possibly burn your phone down, and in the best of the situations, just make the underlaying problem worse.
The phone backlight works quite straight forward in terms of components, as you will only find 5 parts concerning directly the backlight:
- The power management IC
- The coil
- The diode
- The Filter
- And the LCD connector.
Most of the time the problem resides in one (Or many) of the last 3 (The diode, filter or connector). I’ve read many times that the problem can be on the coil, but every time I’ve encountered a backlight problem’s never the coil. So, just start looking at this three bad boys before getting it with the coil, as it’s quite a sturdy guy.
Usually, when there’s water damage there’s water corrosion on the LCD connector, and always the most affected connectors are the ones related to the backlight, as the pins are carrying around 20v on them, making them usually black and burned more easily damaged. If this is the case, you may need to clean and reflow the contacts.
The second part to check would be the filter, as they are usually the culprit when the backlight isn’t working… Almost always. The filter is a small black and silver ceramic component, usually sitting near the lcd connector (In some iPhones, or iPads, there can be more than one… But for the iPhone 4 and 5 there’s only one for sure). Take you multimeter and test the continuity on this piece, if you get no continuity, then you got your felon (You can usually SEE the damage too, as the ceramic splits, or breaks, and sometimes you can see a little point of the silver solder below). Just take that bastard out and replace it, in case that you can’t do that (Many times they get stuck, really stuck) just create a jumper there with a tiny piece of conductor. This will fix the issue, but maybe you’ll see some small flickering from now on in the backlight when calling, as this is what that filter worked out.
Third, but not last, there’s the backlight diode (Sometimes… Weirdly named “Backlight IC” but… it’s not an IC, just a diode). To find it just follow back the way of the filter, use your multimeter to get continuity from it to the next component looking like a… welp, a diode! When you find it, just test it like you would test a diode with the multimeter (On diode testing mode) and also get note of the direction of it (this is very important!), if it’s damaged, replace it using the same direction the old had.
If after testing with a GOOD, checked, perfect screen, still doesn’t work, then you can continue down the line and check the coil (It’s never the coil) or the IC, both rarely fail. Just test the coil for continuity and change if needed… And if the coil is ok, and then the IC is the problem… Just… Take it to repair or buy a new Mobo. As reflowing this is too complicated without a lot of experience and good tools.
I hope this helps!