iPhone 6 Burnt VCC Main Pad Damage Advice

[Shrimply Pibbles]

I Have an iPhone 6s with no image it has no liquid damage and very few scratches. The owner say's she went to use and it was dead so unlikely it was a drop.

I Have checked its not software as it is recognized in iTunes and boots fully according to DC.
I can see the back light illuminate when promoting the phone to boot so I know its an image problem
I have diode checked the LCD FPC and all seems fine apart from pin 39 which is OL (pn5v7_LCM_MESON_AVDDN)
This line has a filter so I checked both sides to which both are OL.
This line goes directly to Chesnut via 2 caps (c4006 and c4001) Both caps are Obv OL on the pn5v7 line.It's not the caps as they are 0.000 on the ground as they should.
I then checked to see if there was power and there was none (i checked while booting via dc).

My thoughts are that chestnut could be bad by not generating the voltage needed for the image I could be wrong. I'm assuming PWMC is fine as the phone seems to be booting normally all be it with no image.

I have come here for advice on where to go next, I'm leaning towards a bad chestnut but want to know if I should test for anything else before I even think about changing chestnut or anything else.

Thanks in advance

[tinker_techguy]

your description in the title says iPhone 6, .. I see you mentioned it correctly in the comments. Pin 39 will read OL with Red on Gnd and Black on pin 39, this is the normal reading. Swap the probe around and put Red on pin 39 and Black on Gnd, you should get something like 0.626v in (diode mode fluke 115). Check to see if you got continuity from the Chestnut side of the filter FL4207 to pin 39. If you get no beep the filter is bad.

Also check capacitor C4200 for short to ground here, just because it's common fail, it takes out both backlight and image, but from your description your saying you got the backlight but just check anyways,

[Shrimply Pibbles]

tinker_techguy Your rite, swapped out and read rite, also checked cap anyways and it was all good. Thanks for the help

[Jessa_the_Professa]

Edit the title to say 6s if this is a 6s. PN5v7 "has no voltage" Let's question that, since "OL on PN5v7" is a common troll and rarely actually a problem--remember that some multimeters will read a very high number as OL. I'm going to guess that you did your voltage test without a screen connected--- Let's think about what it would actually take for the phone to produce the negative 5v7 voltage---do you think that a screen is required? Is it possible that some of the lines at the screen connector are data lines informing the CPU that a screen is present and working and that without that maybe it is normal for the CPU to NOT produce signals to induce the display voltages?

Double check your display voltage readings with a screen present.

The common faults here are:
Slight malformation at the connector,
Phone is in DFU mode in which case no image is normal,
a power problem on the 1v8 or PP5v7 line (not PN5v7),
a short at LCM reset at CPU,
or an open line at one of the image data lines at CPU.

[Shrimply Pibbles]

Thanks @jessa_the professa Your rite, troll line. I did do the voltage test without a screen and yes it does make sense that there would be logic set in place to detect screens (massive hint taken on board )
All the voltages seemed good after testing with a screen. I then went through the list you wrote and they all tested fine up apart from image data lines at CPU to at which point the customer was leaving to go home and needed phone back (we live in a tourist area). My guess is it would have been one of them.
Thanks for your help

[Shrimply Pibbles]

Thanks for that, guys @jessa It won't let me edit the title? Sorry auto corrected and didn't notice. I am out of office at the mo and will read this properly when I get back. Thanks for help

[Sly]

Hi shrimply, I'm not in front of a schematic, but the 5v7 line if your reading is supposed to be about 1.something V in diode mode you might get a open reading instead. I was trolled by that before.

I had an iPhone 6 the other day where the front camera would not initiate. I ended finding an extremely small crack at the end of a pin from the fpc connector going through the square data filters (the ones with four legs) I had to be zoomed in at 40x to see it. Might be worth checking. I had to solder a micro jumper from the leg to the data filter.

also, just a though. Even though your customer said it was just laying there and then stopped working. It is very likely that the phone has been dropped countless times before, and the accumulative damage from all those drops and bending simply decided to manifest it self now.

The more I do this kinda of work the more and more I'm seeing issue caused by broken connection vs component failures.