Iphone 6 Plus Touch ID issue after water damage

[yauuik]

Hi,

I've cleaned all the phone, connector, board and everything is running correctly but touch id
I'am just getting into board repair so I looked a lot of videos but I would like to know which things to test first with my multimeter and how.
I dont know is the issue come form the home button itself or around the logic board connector or IC.

Thank you for your help.

[Jessa_the_Professa]

Where was the water on this board? Check the schematics for the word “Mesa” this is the fingerprint sensor chip. You’ll find Mesa power system on the logic board and it’s related components. Then compare their locations to where the water was on this board. If you have a match it might be a board level problem. If it doesn’t match and the Mesa components and connector on the board look fine, then it is likely the button itself. Of course don’t forget rule #1 and try out a new screen first. It could be damage to the long flex connecting button to the board.

[crea2k]

Has the home button itself taken any damage too ?, id inspect the connector on the home button and check you dont have any corroded pads, as iv seen a phone loose touch id before only for it to be a corroded pad to pin problem on the home button connector on the button itself.

[yauuik]

i've not removed the shield but the only place where I saw something was next to the J2118 connector and the U2100 chip. That was like white salt. I cleaned it with isopropyl and they look fine now + there was some black glue over them to protect them I guess. For the home button itself I haven't opened it because i'am afraided to break it. May I test the board/button flex without opening it with just the multimeter ?
I join a screenshot of where i saw the salt.

[Jessa_the_Professa]

Respond to the advice I already gave you on this. Copied from above:
Check the schematics for the word “Mesa” --This is the fingerprint sensor chip. You’ll find Mesa power system on the logic board and it’s related components. Then compare their locations to where the water was on this board.

Question: Do you have a match between where the water was on this board, and the Mesa fingerprint sensor system on the board? Yes or no.

[yauuik]

yes, if I compare where the water was on the board with ZXW, there are multiple MESA lines, but i don't know which one exactly is the sensor one

[yauuik]

Jessa_the_Professa , for the new screen, i just received it without the plate with the long flex cable. may It be useful by just replacing it with the new screen with the same plate ?

[Jessa_the_Professa]

What do you think?
Pick one:

A--I should reuse parts from a water damaged phone that are involved with the very function that is not working.
B--I should get new parts for any water damaged function of the phone that I can to rule out parts problems.

[crea2k]

I don't mean take the button itself to bits, I just mean disconnect it and check the plug on it has good contacts.

[yauuik]

Ok, so I tested with a brand new screen and plate with long flex cable and the problem still exist. I've checked in ZXW around the damaged zone and we have multiple lines with the word "MESA"

PP3V0_MESA
PP3V0_MESA_CONN

PP1V8_MESA_CONN
PP1V8_MESA

MESA_TO_BOOST_EN_CONN
MESA_TO_BOOST_EN

PP16V5_MESA
PP16V5_MESA_CONN

So how start to test and how :-) ?

[Jessa_the_Professa]

Compare diode mode readings to known good board on those lines. Multimeter in diode mode with red probe o ground and black probe on those lines at the connector.

[yauuik]

I've tested the J2118 connector with the number from the "Connection seat resitance" in ZXW since I haven't a known good board on hands and bingo, there is definitely something wrong

PIN 2(OL) should be 460 - LINE AP_TO_I2C1_SCL_MESA_CONN
PIN 4(0.019V) should be 500 - LINE PP3V0_MESA_CONN

PIN 1(OL)should be 450 - LINE AP_BI_I2C1_SDA_MESA_CONN

[yauuik]

What Can i do next ?

[Jessa_the_Professa]

You gotta fix those faults! When you have higher than normal diode mode readings on a line, this means you have an open line somewhere--research the line on the schematic and find the open line, it can be at a connector, a missing filter/resistor/diode/coil or open joint under a chip. For lower than normal diode mode readings, you have a short somewhere on the line--research the line and find the short, it can be any cap or chip. Let us know what you find!

[yauuik]

Thanks Jessa_the_Professa . This exactly where i'am stuck (research the line and find the short). If I click on one of the faulty pin, It show me a red line throught another filter and capacitor then the line is finished, no other red line to the part of the board. So how to test those cap,filter ? Still in diode mode, voltage, resitance ? Do I need to put my black probe on the side on the component which include the red line or also the other side ? I know in most cases the other part is related to ground but sometime no. If you take the FL2119(iPhone 6 Plus) i.e, il you click on the top side you see the red line that goes to ma faulty pin 4. But do I need to test the bottom part of this filter too ?

[Jessa_the_Professa]

A filter is essentially a wire—how do you think a filter might fail? How could you use your multimeter in continuity mode to find out if a filter is good or not?

[yauuik]

May someone tell me if there is a filter FL2159 or just pad for iPhone 6 Plus ? Because i've cleaned it and I only see pads, no filter at all

[crea2k]

Yer its the data lines its a 120-OHM-210MA

[yauuik]

are you sure to see it on a real board ? Because sometime in zxw it writes filter but on the boa Dnjust pas.