All Common Problem Solution For China Phone

How to repair keypad problem in china phone-



First we need to know china phone keypad connected with PCB how way-

(A) Direct on PCB

(B) Flex System (flex cable direct soldering pcb to keypad panel)

(C) Flex and socket system include (flex one side soldering with key panel other side connect to pcb with socket)

(D) only Socket System (here have 2 socket, 1 with key panel others with pcb)





Keypad problem have various type-

1. All key not work.

2. some key work and some other not work.

3. sometimes work and sometimes not work.




1. All key not work
china phone all key not work for this type of problem-

(A) though its touch screen phone, first try to disconnect touch panel line from phone pcb or display flex (4 line)

(B) though not solve and keypad direct on pcb first you try to good clean full pcb with cleaner.

(C) though not solve now you try to format/flash your phone because some time key problem come from software problem.

(D)
though still not solve now you check must be CPU. 95% china phone
keypad directly going in cpu. and other 5% first going to resistor or
capacitor near the cpu or keypad than going to cpu. so now first check
them than you can try to re-hot, re-soldering or changing cpu.

(E)
though its flex or socket system, first check GND connection
continuslay pcb to key panel. next check full flex or socket all line
going continuously pcb to key panel or not. also sometimes flex or
socket shorted with other line or gnd so check also them.

(F) Also you can check all key anyone is short 2 line.

(G) sometimes keypad line broken from cpu pin on pcb to key panel, so check them.




2. Some key work and some other not work-
Some key work and some other is not work for this type of problem-

(A)
maximum time this problem we face for flex or socket system keypad. so
check flex cable and socket all line any line is broken or not and
though need change them. and check all key connection on key panel.

(B)
though its direact on pcb, some of key line broken internaly. and
maximum china phone have alternative test point near every key or with
other key on keypad. so check them with multimeter and though need
connect to not work key with near testpoint or other working key.

(C)
common problem is keypad metal ball (which is short 2 line on key when
we press) sometimes its damage for phone water damage or over key
voltage, so clean them or change.

(D) also try to check line continuously from cpu to not working key.



3. sometimes work and sometimes not work-
this problem come from this defect-

(A) flex or socket system keypad any line is bad soldering or do lose contact. check them and
re-soldering or keep there line join with extra ware.

(B) for cpu bad soldering or cpu pin is broken. so re-hot or re-ball cpu.


I post here keypad common problem solution, hope it will help you to fixing your keypad problem.

Repair Display Problem Of China Phone-


China Mobile Display Type-
1. Flex system
2. Connector/socket system



Display Problem Come From-
1. Display Damage/Broken/ Broken Microchip area in display
2. Flex and parts damage
3. connector damage on both (pcb and display flex)
4. wrong software.
5. Display line broken from display connection to CPU.
6. CPU internal display section Damage.



1. Display Damage/Broken/Broken Microchip area in display
For this type of problem, have no way without display change (every one know it). so just
change display.
Display Microchip area on display panel-

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2. Flex and parts damage
Sometimes we can see with our won eyes where is broken flex line or any parts.
but maximum time we can't see it normally. so we try to repair our display, when we confirm
phone show display problem only for display panel not for any type of pcb defect. can we
confirm it by replacing a good display on pcb. when we 100% confirm problem only on display
panale than we can try to repair it. otherwise first fix other problem.

For this type of problem can you repair flex cable with extra wire, but first need to
calculate flex cable all line with multimeter. some times line cross flex cable 1 side to
another side by in flex. so check them. and you try to change this type or parts, see picture-

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here i mark some parts and only one type of display, other display parts find by your self.

though possible, change all parts from another display (which is broken but parts is ok)



3. connector damage on both (pcb and display flex)
Connector/socket system display create problem from there connector. so check simpaley there
all line with multimeter and fix them. though need join them with extra wire from direct pcb
to display. also you can change both socket.



4. wrong software
for wrong flash file or software problem we face white screen problem. so take any step before
do 100% Confirm its not for software problem.

we maximum time face this problem after flash or format. so after flash or format when a dead
phone is power on. we can 90% confirm its for wrong version flash file. so first see your
original flash file version than backup it and next flash phone with this same version
new/another ok file.


5. Display line broken from display connection to CPU.
98% china phone display line going direct cpu and other 2% have display ic. and sometimes
display line broken or break soldering from cpu to pcb middle point. just cpu bad soldering.
so can you try to re-hot cpu with your won risk.
also sometimes pcb internal line broken from cpu to display connection point. so check them
and fix them. (but do it after changing a good cpu though still display not ok)


6. CPU internal display section Damage-
Sometimes phone all section is working ok (without display) but have no display still after
change a good display (soft ok also) now you need to change must be cpu. because many time i see
phone all section work ok but have no display, after changing a good display phone is ok
100%. can anyone question, though its problem from cpu so how phone all section work ok. ans is
- phone all section work ok because only display area damage internally in cpu but all other
section have no problem.


i explain it from my work and experiment. hope it help to you for repair a display of china phone.
now you can understood you start from where to repair a display. A
wrong decision can't give you a success so read it carefully than do
with your won risk.

What is TX RX?

tx rx is type of connection which will help to you to connect your
phone with pc for software operation. its just a type of connection
name.


what is cpu?

Central processing unit. A parts of phone. its type a head of phone.
all phone have cpu but for china phone cpu is important for repair this
phone. china phone have various type of cpu.


why cpu is important for china phone?

All other phone have cpu, uem, upp but for china phone cpu is important
for repairing because various china phone cpu support various
tool/device when you do software operation in phone.


How to know cpu type/model?

now many of device auto detect cpu type so no problem to know which cpu
use in this phone which you want to repair. also you can open the phone
and can see what cpu use in phone/what name write on cpu.

MTK
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Spreadtrum
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Infineon
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Sky/Skyworks
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ADI/AD
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Philips
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Agree
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TI / Power Management
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VIA

SAMSUNG

SI4904

ANYKA


what is flash chip and RAM?

flash chip store phone software in it. and RAM is extra built in memory
which give space to phone and flash chip to extract phone software and
operating in his memory when phone is open/running. some china phone
flash chip and RAM include in one chip and some in cpu. so if your flash
area or ram area is damage in flash chip, you must need to change total
chip (CPU, Flash IC,) using many type of companies chip with under
various model name, as like Samsung, Toshiba, Intel, ST etc


Flash chip name/model is important for china phone as like cpu?

Not like cpu but its important because when we flash china phone if we
know what flash chip use in it then we can find perfect flash file.



what problem with china phone model name?

model name is not a big matter for china phone. because with same name
have many many phone with deference pcb, pcb design, cpu, flash chip,
gate up, software etc.


What need to know about a china phone when we repair?
1. CPU Type
2. Flash Chip model
3. Original software/flash file version.
4. Phone TX RX.

Flash file version is important for china phone?

Must. its very very important for china phone because though you lost
your original (when manufacture company published phone) flash version
or not know which file have in it first time, you got problem when you
flash your phone. for flashing with wrong version/model flash file you
got this type of problem-
1. Flash done but phone dead
2. white screen (no incoming/out going call)
3. white screen (with incomeing/outgoing call)
4. Keypad not work
5. Sim not valid
6. Sim blocked
7. Phone hang after power on
8. no network
9. have network but show emergency (this problem also do for power ic or bad connect sim or sim connector problem)
10. phone restart continuously.
etc.

Which tool or device?

many of free tool published in market for mtk, infineon, ad,
spreadtrum, sky etc. but alwayes device give you a complete solution.