How You Repair A Dead China Phone:

How You Repair A Dead China Phone:

First we need to know why a phone is dead-
1. For Software
2. For Hardware

1. For Software-

Flash is its final solution, but mtk cpu 90% phone done by format. if its MTK,SPD,AD, SI4904 cpu first try to format than try to full flash your phone with a good and perfect flash file. and other cpu haven't format option, so direct flash them. when you flash careful about original flash file version.

A. what you do before format or flash-

Always remember, before format or flash of your any china phone must first backup your current flash file if phone is dead, also do it. because it will help to find its original flash file version and many other.

B. What you need for flash or format a china phone-

(1) Connecting device (also your can do it with usb to serial cable but a device/box can give you full/final solution)
(2) Phone TX and RX.
(3) Need to know phone cpu type/model, flash chip type/model, Flash file version.
(4) For Flash need a good flash file which same to your phone original flash file version.

C. What problem you face for wrong flash file
(1) phone still dead
(2) white screen
(3) keypad not work
(4) phone hang after power on
(5) keep restarting
(6) no network
(7) etc.

Tool For MTK Flash info

2. For Hardware-

when a dead phone not possible to repair only with software you need to repair phone hardware.

Which hardware you need to check for dead phone-

(1) when you try to flash if phone not boot check power source/battery voltage/V+ pin in phone connector. just do confirm phone found enough voltage for software operation.
(2) if phone power source is ok but still not boot, do confirm your tx and rx is 100% working/tested.
(3) if tx rx is ok, than check your phone connector, its tx rx pin is confirm connect with cable and internal connector pin is joint on pcb perfectly.
(4) if pin is ok, maximum china phone tx rx going to cpu after crossing a resistor or capacitor so check them.
(5) if resistor is ok now you need to check boot diod, all phone have no boot diod so last try is check cpu tx rx pin.
(6) if boot is ok but phone not receive flash file, maximum time this problem coming from flash ic or ram (maximum china phone flash memory and ram have in one chip). so you need to try first re-hot it if still not solve change it.
but its true flash chip/ram always show error not only for them, sometimes cpu to flash chip/ram connection lost for bad cpu pin or bad cpu soldering on pcb. so check both of them.
(7) phone flash ok but not power on (although file is 100% correct) , for it you need to check

Flash chip/ram (95% include in 1 chip)
Clock crystal and battery
26mhz (near rf ic)
Rf ic,
Power ic and v+/b+ way
Bt ic
Last try is cpu.

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-

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-

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.