iPhone 6 Backlight Repair - Gone Awry

[ScreenFixing]

1.) Model of device and anything you know about its history.

Phone 6 - Drop damage and bend damage to the housing. Drop occurred a few days ago, followed by backlight failure. Phone was opened by Batteries+Bulbs who sent the customer here.

2.) Physical exam findings---what did you see under the scope

Found all filters were good. Proceeded with replacing the backlight circuit. During the backlight repair L1219 shifted and came off the board, I replaced it with a donor. After replacing the circuit backlight anode and cathode lines were testing properly. Went to boot phone and got no backlight/no image. Checked the Backlight driver and found that it seemed a little off under scope, so I removed it. Booted phone to verify no backlight and phone would boot with image. After replacing the driver again, we found the phone was no boot. Removed driver to make sure nothing was short under and attempted boot, notta.

Phone was booting when it came in as I tested with a no backlight cover LCD.

3.) Tests done and results. Example: DC power supply behavior, diode mode measurements, etc.

DCPS: Currently pulling .06 then .05 then .00 after prompt to boot. No short on VCC Main.
VCC Main is 4v provided by DCPS.
Checked voltages on pull up resistors around CPU, all loop 1.8v as expected as phone loops.
Removed entire backlight circuit again, same behavior

4.) Describe prior repair attempts in your hands or previously

Previous screen repair by another company. Backlight circuit replaced by us as part of this repair.

5.) What is your current diagnostic thinking?

I don't see any solder balls popped out around CPU but I am assuming that somehow despite being well protected, CPU is short causing no boot. I want to confirm though. We used standard heat and standard practices to do backlight repair as we have done a lot of without issue. I checked the backside of the board and have removed all the items that I installed except L1219 (which is appropriately testing at .95v). I don't see a cause, which makes me assume it's hiding.

I am in the process of clearing any of the black epoxy as I am able from surrounding components that could have floated due to heat, but so far everything is good. I am also thinking that the board was potentially more susceptible to damage due to it's the bend in the housing.

Thanks,

Nate

[Jessa_the_Professa]

Hey there Nate,
All of that seems pretty reasonable. The only thing to rule out is software. Let's say that at some point the bl driver was askew and bridged the i2c0 SDA and SCL lines during a boot up operation. That kind of squirrelyness could have corrupted the software (as is often the case with tristar damage for example). So now you have essentially a boot loop of sorts. You could try holding down home button to boot to recovery mode and then update/restore and see if it can pass an update.

Another possibility is that because 1v8sdram goes under both bl driver and tristar that perhaps a problem at bl driver damaged tristar---super unlikely but on the list.

I would pick up the pullups and reseat them and make sure that you don't have anything going on with the bl driver pads--for example if a pad was nudged to ground on the edge of it then that could similarly both the data lines. Once I had an invisible hairline crack in one of them from tweezer damage removing the shields.

I think the CPU is pretty robust in that spot so i'd be surprised if this was dead cpu.

Let us know how it turns out.