IPhone XS Max No Touch: Difference between revisions

IPhone XS Max No Touch
Device	IPhone XS Max
Affects part(s)	Motherboard
Needs equipment	Soldering Iron, Hot-Air Station, Microscope
Difficulty	◉◉◉◌ Hard
Type	Soldering

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Latest revision as of 22:05, 18 August 2025

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Problem description

The device turns on but touch does not work

Symptoms

Touch doesnt work.

Solution

The most common issue on iPhone XS Max with no touch is a disconnection between the top and bottom boards, but in this guide we will go over diagnostic steps that should cover the main causes of no touch.

Diagnostic Steps

The first step is to always rule out faulty parts. Start by testing a new display.

If a new display doesnt not solve the issue inspect the Touch FPC for any physical damage or liquid damage.

Take diode readings of the Touch FPC and compare them with the image on the side.

If everything is ok the next step is to check if the main touch voltages are present.

These voltages can be measured here, keep in mind that these voltages may only show up with the device powered on and a display connected.

PN6V7_RACER

PN3V5_RACER

PN10V0_RACER

PN1V8_TOUCH_RACER_S2

PN1V1_RACER

PN5V25_TOUCH_VDDH

If these voltages are present/or missing the next thing to do is split the boards, the most common issue is to have a crack on a solder joint between the interposer and the top board or a ripped pad.

The first thing you should do after splitting the boards is to check for any ripped pads, if you have any you need to check with a program like ZXW and see where that line goes.

Test with a tool similar to iSocket and turn on the phone and see if Touch works, if it is all you have to do is to reball the motherboard.

Repair Steps

If by replacing by trying a new display the touch fault is solved all you have to do its to replace the display.

If there is a any physical damage to the FPC the solution is to replace it. The best method is to use a hot air station to desolder the old FPC, clean the old solder from the motherboard, apply new solder, align the new FPC, and use the hot air station to solder it. Be careful not to use excessive heat, as you may cause a solder bridge under the motherboard.

When taking diode readings of the FPC, if you measure a line that should read, for example, 0.500V but get 0.100V or 0.000V, it indicates a short on that line. The best way to trace the short is to inject voltage into the line with a DCPS and use a thermal camera to identify which component heats up. Fallow this guide how to find the short Short Circuits - Repair Basics

If you measure a line that should read 0.500V but get OL (Open Line), it indicates a disconnection in the circuit. To trace the issue, consult the board view to follow the line’s path.

If Touch works fine using the iSocket tool the motherboard must be reballed.

If Voltages are missing this may be due to a faulty U5600 (LM3373A2YKA) this creates most of these, i have seen this IC faulty 2 times.

U5600 can be found online easily on many suppliers it is also present on iPhone X , iPhone XS and iPhone XS Max.

If you have ripped pads they may not be needed check on a boardview software like ZXW what they do if the line you check has the name "RACER" or "Touch" it needs to be rebuild.

If you need to rebuild a pad it is recommend to watch this video by rewa on youtube: https://www.youtube.com/watch?v=I_6xZVY7sFM

Final Testing

After assembling the phone, ensure every function is working as expected, not just the touch circuit.

@@ Line 1: / Line 1: @@
-'''820-3662 NO NUMERIC KEYS / CAPS LOCK INVERTED / INPUT DELAY - TOUCHPAD ISSUES'''
+{{Repair Guide
+|Device=IPhone XS Max
+|Affects parts=Motherboard
+|Needs equipment=Soldering Iron, Hot-Air Station, Microscope
+|Type=Soldering
+|Difficulty=3. Hard
+}}
+{{stub}}
+== Problem description ==
+<!--
+Provide a concise description of the issue here. Be  as specific as possible to help readers quickly determine whether or not this is the exact problem they are facing.
+ -->
-The device arrived with the numeric keys on the internal keyboard non‐functional, despite a complete keyboard replacement. Visible moisture and sulfation were detected near the keyboard’s SPI controller (U4801).
+The device turns on but touch does not work
+[[File:IPhone XS Max Touch FPC Diode Values.png|none|thumb|500x500px|iPhone XS Max Touch FPC Diode Values]]
-🔍 '''Step-by-Step Diagnosis'''
+== Symptoms ==
+<!--
+Detail all measurable or observable symptoms in this section.
+-->
+* Touch doesnt work.
-Visual inspection: Corrosion was found near the keyboard/trackpad controller area (U4801).
+== Solution ==
+<!--
+If the issue has a single, specific solution, provide it in this section and delete the sub-headers below. Otherwise, if there are multiple potential causes for the problem, outline the process of identifying the root cause and offer corresponding solutions below.
-Voltage drop across R4814 (relevant resistor in the SPI circuit) was checked and confirmed expected values.
+-->
-'''''Chip replacement attempts:
+The most common issue on iPhone XS Max with no touch is a disconnection between the top and bottom boards, but in this guide we will go over diagnostic steps that should cover the main causes of no touch.
-'''
-'''First attempt:'''
+=== Diagnostic Steps ===
+The first step is to always rule out faulty parts. Start by testing a new display.
-Replaced U4801 with a donor chip from board 820-3476 (MacBook A1502).
+If a new display doesnt not solve the issue inspect the Touch FPC for any physical damage or liquid damage.
-🟡 Result: Keyboard worked, but Caps Lock LED was reversed (lit when lowercase, off when uppercase).
+Take diode readings of the Touch FPC and compare them with the image on the side.
-'''Second attempt:'''
-Used a chip from MacBook A1278 (Unibody).
+If everything is ok the next step is to check if the main touch voltages are present.
-🔴 Result: Severe input delay, no trackpad and overall poor keyboard behavior.
+These voltages can be measured here, keep in mind that these voltages may only show up with the device powered on and a display connected.
-'''Final solution:'''
+PN6V7_RACER
-Replaced with U5701 from donor board 820-3332.
+PN3V5_RACER
-✅ Result: Keyboard fully functional, Caps Lock LED working properly, no delay, trackpad also fully operational.
+PN10V0_RACER
+PN1V8_TOUCH_RACER_S2
-'''⚙️ Technical Conclusion'''
+PN1V1_RACER
-The U4801/U5701 keyboard SPI controller contains firmware/configuration specific to each board model. These chips are not freely interchangeable between different MacBook series (A1278, A1502, A1398, etc.).
+PN5V25_TOUCH_VDDH
+[[File:IPhone XS Max Touch Circuit Voltages.png|center|thumb|418x418px]]
-⚠️ '''Using an incompatible IC can cause:'''
-Reversed Caps Lock LED logic.
+If these voltages are present/or missing the next thing to do is split the boards, the most common issue is to have a crack on a solder joint between the interposer and the top board or a ripped pad.
-Noticeable input delay on keys input.
+The first thing you should do after splitting the boards is to check for any ripped pads, if you have any you need to check with a program like ZXW and see where that line goes.
+[[File:Ripped Motherboard Pads.jpg|center|thumb|Example of ripped motherboard pads]]
-Malfunctions with the trackpad or power button.
-✅ '''Key Takeaway'''
+Test with a tool similar to iSocket and turn on the phone and see if Touch works, if it is all you have to do is to reball the motherboard.
+[[File:ISocket tool.png|center|thumb]]
-“The keyboard IC (U4801/U5701) must come from a firmware-compatible logic board. Although they are electrically identical, their internal configuration depends on the board model and its interaction with the SMC.”
+== Repair Steps ==
-— Diógenes el Perro
+If by replacing by trying a new display the touch fault is solved all you have to do its to replace the display.
-🛠️ Note: Neither the BIOS nor the SMC were reprogrammed during this repair.
+If there is a any physical damage to the FPC the solution is to replace it. The best method is to use a hot air station to desolder the old FPC, clean the old solder from the motherboard, apply new solder, align the new FPC, and use the hot air station to solder it. Be careful not to use excessive heat, as you may cause a solder bridge under the motherboard.
+When taking diode readings of the FPC, if you measure a line that should read, for example, 0.500V but get 0.100V or 0.000V, it indicates a short on that line. The best way to trace the short is to inject voltage into the line with a DCPS and use a thermal camera to identify which component heats up. Fallow this guide how to find the short [[Short Circuits - Repair Basics]]
+If you measure a line that should read 0.500V but get OL (Open Line), it indicates a disconnection in the circuit. To trace the issue, consult the board view to follow the line’s path.
+If Touch works fine using the iSocket tool the motherboard must be reballed.
+If Voltages are missing this may be due to a faulty U5600 (LM3373A2YKA) this creates most of these, i have seen this IC faulty 2 times.
+U5600 can be found online easily on many suppliers it is also present on iPhone X , iPhone XS and iPhone XS Max.
+If you have ripped pads they may not be needed check on a boardview software like ZXW what they do if the line you check has the name "RACER" or "Touch" it needs to be rebuild.
+If you need to rebuild a pad it is recommend to watch this video by rewa on youtube: https://www.youtube.com/watch?v=I_6xZVY7sFM
+== Final Testing ==
+After assembling the phone, ensure every function is working as expected, not just the touch circuit.