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The Mi 9 is a mid-range smartphone by Xiaomi which was released in February 2019. Featuring a 6.39" super AMOLED display, a main camera with 48 MP plus an ultrawide 16MP and a 12MP telephoto lens, an under-display fingerprint reader and a 3300 mAh battery with fast wireless charging.

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Fingerprint not working after screen replacement

Hey guys

have replaced the screen (whole unit with frame) on this Xiaomi Mi 9

afterwards the fingerprint Sensor did not work properly. It hardly Scans the initial fingerprint but won’t unlock the phone with it or allow any other fingerprint functions.

I have already removed it and replaced it again. as it is embedded into the Display Unit I Wonder if this is a problem concerning the display unit or the fingerprint scanner itself.

if it is the fingerprint scanner, would it even be possible to replace it or is it like on iPhones „married“ to the motherboard?

would appreciate your support guys

keep fixing

peace

Answer this question I have this problem too

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3 Comments:

I feel like it has to do with the screen. Where did you get the part?

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Did you fix it? Have the same issue after my screen replacement

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I have the same problem here.

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5 Answers

Exactly the same here.

Bought Frame + Display on ebay (Germany). Everything works perfect except the fingerprint sensor.

"Learning" a finger is hard. Only every 10th scan is recognized. Other 9 fail with messages like "too fast" or "dirty sensor".

Unlock has two different behaviors:

1) On ambient display: It never works (which previously did). The sensor "scans" for around 300 milliseconds and fails. With the old display it took the same amount of time but it worked.

2) After pressing power button: It takes about 1 second (which is a really long time) for the scan to be completed but works most times (9 out of 10). Previously it worked much faster.

/edit

Just found out that it does NOT work properly in the “power on button” state. After 1 second the device gets unlocked, BUT it also gets unlocked with unknown fingers! Maybe it focusses something in the display?

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I highly doubt it's the phone's fault, but rather a bad quality part. This is why you have errors

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Apparently the latest software blocks the figure print replacement from working.

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I’d first check if the fingerprint sensor or the scan hole are dirty, and clean them. Afterwards, try erasing all the fingerprints and re-adding them. It’s possible that a software update started to pair displays to the motherboard, so one way of fixing this would be using a custom ROM. Hope this helps.

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Late update: just had a client with a similar problem.

Turns out the fingerprint sensor is really sensitive to the positioning, so if you bent one of the plastic positioning pins even slightly, it will register the first few scans, but fail after. I'd suggest getting a new one if that's an option, as well as cleaning the glue residue, then adhering the new one in place with the right thickness of new adhesive tape (I think one or two layers of a B-7010 type double-sided should do, does require some trying however).

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https://www.youtube.com/watch?v=9jKmbfP2...

This is work propertly :)

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Hi all,

I have recently replaced the display of the Mi 9 (from Aliexpress).

After installation the fingerprint worked and when I tried again after the factory reset the input was failing and after multiple tries, I was able to add the fingerprint.

One way I overcame the fingerprint unlock problem is by adding the same finger multiple times.

Block Image

I tried to do the calibration through CIT but I'm getting Auto_Exposure test fail.

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