Released on September 19, 2014, this 4.7" screen iPhone is the smaller version of the iPhone 6 Plus. Identifiable by the model numbers A1549, A1586, and A1589.

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Unable to setup touch ID, board repair

Hi all! I bought a dead iphone 6 which I repaired just by replacing two vcc_main caps near backlight and working a bit on the backlight circuit itself, now it's fully working except that it doesn't let me configure a new finger. I don't get the error message upon boot that is typical when you let the home button unplugged or when you connect a different one, but rather a message when I go to set a new finger up. This leads me to believe the sensor is being recongnized but is lacking something, power or data.

Before I go into the board itself I should point out that I tried a known good long flex and also tried its original flex on a working phone.

No physical damage on any flex or the board.

Since I was working on the BL circuit which is close to the little LDO that gives Mesa the 1V8 line I replaced it but it didn't do any difference.

I did a diode mode measurement on all pins on that connector and they tested good against a working, known good board.

Now before I start replacing other chips just because, I want to understand the power sequence of the sensor.

As far as I can tell, the sensor sends the MESA_TO_BOOST_EN signal and then the boost converter should start sending the 16.5V and the other two voltage lines too, but I don't understand at which point I should be seeing them.

My first thought is when I try to set up the new fingerprint or on the lockscreen but no power or the enable lines were present at that time. What am I doing wrong? Maybe the previous owner unplugged it while energized and that killed the sensor and all this work is futile wich would suck but is pretty likely at this point

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1 Answer

Chosen Solution

Your troubleshooting is sound. I've never looked at the timing sequence but you could try measuring this on a known-good phone by soldering some small wire to the PP16V5_MESA line , as well as the MESA_TO_BOOST_EN, PP1V8_MESA_CONN & PP3V0_MESA_CONN to see what the timing sequence looks like on a good phone. Then do the same on your DUT to see what's different.

Also take a look at AP_TO_I2C1_SCL.

Hopefully you'll see something that helps and report back!

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Hi Minho thanks for answering! You're always giving me a hand. I don't have a known good I can solder on the board, my other known good turned into known bad after I took the pmic off of it for another job, and the measurements I did were on a client's phone that came in for a screen replacement and it didn't feel right to start soldering stuff to their board. Measuring yes because it's less intrusive.

Now what I have found measuring on my board:

-3V0 and 1V8 lines seem to be always on (the 3V line comes from the PMIC and the 1.8V from a little LDO that has no enable pin or anything. Both lines are present, nice steady voltage

-16V5 line turns on when you touch the home button, goes up to about 16V and drops slowly down after you let go the button, maybe it should go up further but it seems ok to me (maybe my multimeter isn't fast enough)

-The enable line I wasn't able to measure, but I think it's fine because the 16V5 comes up, if not it wouldn't be present

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Those measurements look okay.

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Hi again! I was about to no-fix this and last night I restored it again and now it works great! Go figure... so for future reference this is what I learned: 1V8 and 3V0 are always present, when you touch the home button the enable line gets to short pulses and that gets the 16V5 line up. I'll mark you answer as the fix. Thanks man, you're always here! Really appreciate it

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Rodrigo Maero will be eternally grateful.
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