iPhone X Boot Circuit Diagnosis and Maintenance Online Course
Hello, guys
In the last course
we have learned how iPhone X boot circuit works
Today, We will learn iPhone X boot circuit diagnosis and maintenance
First, let's take a look at the iPhone X motherboard
As we know, iPhone X motherboard with two layers
the upper player and the lower layer they are banding together
and to tell the difference between the upper player and lower layer
we will call the upper player as logic board
And we will call the lower layer as signal board in the future courses
iPhone X current is more than 200mA once trigger to boot
this case is a little different
This is not when connect with DC power
This is connected with DC power
then you press power button or use Tweezer to trigger start up the phone
And the current is just jump from a relatively high value
And here is the curve for your reference
this iPhone X boot current curve for your reference
you can see, normally the current for the boot process
It goes like this
It start from around 50mA
but in this case it's more than 200mA
So, obviously there's something wrong with this boot process
In this situation, let's see how to do the troubleshooting
First
separate the motherboard
and check the logic board only to see if there is any current leakage
If there is currently leakage
then we check the logic board
use rosin inspection method to locate the abnormal areas
And there are different situations
The situation one is the PMU get heated
let's go back to block diagram to have look first
Remember this block diagram
for the boot process PMU should work first
then output some powers
output 15 set of powers
and 3 set powers to CPU and NAND Flash chip
So in this case
we find PMU heat
then the problems is might come from the outputted power lines with some short
Or maybe the PMU itself. Inside, some circuits get shorted
So first
Let's check the PMU output 17 set of voltage related circuits
by measuring diode values on the relative components
For example
This is the power outputted from PMU
there are 15 sets power output from PMU to CPU
We can check each power rail
by measuring the diet values on the relevant components on the rail
For example
for the PP_CPU_PCORE
We can measure whether this power rail is good or not
by check the diode value on this capacitor C2701
For other circuits, same.
We can random pick one component
related with this rail and check the diode values
So if you find the diode values normal
for example, here
we measure all the 15 and 3 sets of power rail diode values
They are normal
then it means the output parts is OK no problem
then, the problem should be from the PMU
So if they are normal
PMU problem may be poor soldering or get damaged
So we should recall the PMU or replace PMU with a new one
and go back to here
If we measure the outputted power rails
the diode values is abnormal
Then we're going to track the abnormal rail
find out and replace the relevant abnormal components or chip
Okay
Let's come back to here
Situation 2, is other chips get heated
For example
the USB IC, backlight IC, display IC
if they get damaged can also cause
the boot current start from maybe over 200 or even higher
So you're going to feel which IC is heat
and then tracks relevant circuit
and repair by replace chip or replace components
another situation from the very beginning
We separate motherboard and check the logic board only
to see if there is any current leakage
If there's no current leakage then what does that means
There is no current leakage on logic board
then it means the current leakage
Actually it comes from the signal board
This signal board
So we should apply some rosin on the signal board
then combine signal board with logic board
and put them into the socket
the socket (the fixture)
then apply power around 20 seconds
After that
take out the logic board and the signal board
And check if there're any components
The surface rosin get melted
If you find any components with rosin get melted
this should be the problem
Then you're going to get this chip or component replaced
So this is the troubleshooting process for this case
And also we have some tips
First, the Qualcomm board
Only the logic board is required to start up
No need to separate the motherboard
For the Intel board
Both logic board and signal board are required to start up
So we should use rosin inspection method to check the logic board first
If the logic board with no problem
then we can do the separate and check the signal board
This sometimes can save our time
because not all repair need to separate the two layers of the mother board
And One more tip
for iPhone X repair, the fixture
for example the socket is required for efficient test process
In order to explain to you more intuitively
We take this damaged board as an example
to show the detailed troubleshooting process
First, run cosmetic inspection of the motherboard
The motherboard is not deformed or water damaged
Then connect motherboard with DC power supply
We can see there's no current leakage
Judging by this
the three main power supply rails
PP_BATT_VCC, PP_VDD_MAIN and PP_VDD_BOOST
are in normal condition
Then get motherboard booted up with tweezers
The boot current is larger than normal value
The fault is probably related to the 17 power supply rails
which output from PMU
now we separate the motherboard
to confirm whether fault is related to the upper layer or the lower layer
connect the battery connector on the upper player with DC power supply
then get the upper layer booted up with tweezers
the boot current still larger than normal value
So our next step is to check the 17 rails
output from PMU one by one
Let's start with PP_CPU_PCORE first
Locate C2701
One of the test point of PP_CPU_PCORE on the bitmap
then run diode mode measurement of this capacitor
The measured value is normal
So continue to measure the test point of the remaining 16 rails
Judging by the measured value
PP3V0_NAND has shorted
So we can locate the fault components with rosin detection method
Set the output voltage of DC power supply at 3 volts
then get black pin to ground
and red pin to the test point
We can see some rosin on the surface of this component melted
And this one is C2649
Judging by this, C2649 has been damaged
Remove the black glue on the surface first
Then we can just tick it off with tweezers slightly
after that, measure the diode value again
This time we can see the diode value is normal
then connect the battery connector with upper layer with DC power supply
and get upper player booted up with tweezers
Let's see the boot current
So this time, this boot current is in normal condition
Next thing we need to do is to solder the two layers together
Put the two layers on the heating platform to solder them together
After that
get the display assembly installed
then get battery connector with this power supply
get it booted with tweezers
to see the boot current
The book current is normal
And let's see, the phone comes with normal display also
and can access to the system
Fault cleared
So iPhone X won't turn on with large boot current issue fixed perfectly
More iPhone X troubleshooting courses will be launched in this week
You can visit REWA academy website academy.room.tech to learn more
And hope REWA repair course
could be helpful to improve your repair skill and knowledge
See you next course
Bye