iPhone 6 - No flash (Only comes on for about 1 second)

[Sly]

Hi,

Main question: What lines are responsible for the flash?




History:
We purchased an iPhone 6 from a supplier with known touch screen issue.
When we got it, we noticed it had a really cheap aftermarket screen on so we replaced the screen, and tested fine at the time.

Few days later we sold the phone, but it came back with touch screen issues.
I've reflown the touch IC, and everything worked fine, gave it back to the customer.

About a month later, the customer came back with it with a cracked screen, problems with weak wifi, and the flash not working properly.

I've replaced the screen.
The weak wifi was due to the wifi antenna being partially disconected
and I'm still troubleshooting the flash problem.

The flash only comes on for about 1 sec, and is very faint. Tried replacing the rear camera, and the flash it self, and have the same result.

Next I'm removing all the waterproofing around the components around the lcd connectors, and Fcam and all that looking for loose components.

I don't know if the flash was working right after the touch IC reflow since I did not think about testing the flashlight.

I'm not sure if the flash not working is a due to the drop, or the touch IC reflow yet.

From the wifi antenna being partially disconnected, I would assume that it might of have fallen hard although the customer claims it was only drop from about 1 to 2 feet when the screen broke, but the phone belongs to her teenager.

I never real had to troubleshoot flash yet.

Is the flash related to Driver_to_LED?

[Jessa_the_Professa]

Have you ruled out left hole LSD and liquid damage out at power button? Flash is anything with LED Driver, and lines with names like strobe, gsm burst, muon, warm/cold LED. In iPhone 6 you can find flash lines at power button and at the flash (led) driver which could have been bothered by a meson reflow.

[Sly]

Hi,
There is no LSD.
No signs of liquid damage.

I have tried with a different power button flex from my spare parts, with the same result.

Since my last post:
I have took out all the silicon around the components of FPC J2321. I did not found any loose components there. I've checked continuaty from the fpc pin to the other side of the following filters:

FL 2322 LED Strobe EN
FL2329 AP_BI_RCAN_IC_SDA (R0705 is also well soldered in place from what I can see)

I have found 3 "loose" components on the right side of J2118:
C2100
FL2150
FL2133
But those a regarding MESA, and I don't believe they were actually disconected since I did not have any problems with the home button, or touch ID. (I believe that's what MESA is responsible for). I've possibly knocked those components loose a little as I was removing the underfill since I was using a dull blade at the time. Either way I've resoldered the side of them that were loose, and no change in regards of the flash.

I've removed all the silicon over the components under J1111 and found no loose components.

What's next:
*I will try with a known good power button cable, since the last one I used was from spare parts.
*There is a few resistors and components on the other side of the board that is connected to U1602. I don't believe that does are underfilled, but I will check for accidental damage while working in that area.
*I will remove the CPU shield as I'm considering resoldering the U1602, although when looking at the board, this chip seems to be very far from Meson for it the get accidentally reflown. If U1602 was accidentally reflown, I would of have expected other components that are nearer to Meson and udnerfilled to have shifted as well, but no components under J1111 were loose...I'm not too keen on working on U1602 because of the hard underfill that covers it, and it's extreme proximity to the CPU, hence why I'm saving this for last.

Any chance that this might be a software problem?

Thanks for you help Jessa

[Sly]

Update:
Just found that PP_STRB_DRIVER_TO_LED_COOL's connections from the FPC J0801 all have a Open line reading with my diode mode measurements. The warm side is reading with values comparable to ZXW values.
I was able to get the flash to come on while applying pressure over the cpu plate.U1602 must be disconnected. I'll update once I'm done working on U1602

[Sly]

Solved:

It was a bad connection in U1602 for the driver to led cool.
I've removed the chip and installed it again. The flash works normally again.

I don't know if this was due to the fall damage or from when I reflown Meson. I need to start testing the flash as part as my testing routine.

Thanks for your help.
I find it often very helpful to simply talk (or write in the case) to someone else about the problem I'm trying to resolve. It usually helps to clear up my thoughts.

[Jessa_the_Professa]

When the problem is generated after heat, then on your differential diagnosis what floats to the top of *most likely* is any chip that has underfill and could be affected by heat at the first surgery. That really points to flash driver in this case. I’m glad you found it! I have seen this maybe twice so it isn’t common but backlight driver after 6 meson sure is.