HOW TO REPAIR KEY PAD PROBLEM IN CHINA PHONE
First,we need to know that china phone keypad is connected with PCB this 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 keys not working.
2. some keys works and some other not work.
3. sometimes work and sometimes not work.
1. All keys not work
China phone all key not work for this type of problem-
(A) though it is touch screen phone, first of all try to disconnect the touch panel line from the phone PCB or display flex (4 line)
(B) though not solve and keypad still direct on PCB, first you try to clean the PCB with cleaner.
(C) though not solve,now you try to format/flash your phone because sometimes key problem comes from software problem.
(D) If not still solved,check the CPU. 95% of china phone keypad is 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 then you can try to re-solder or charge the CPU.
(E)If it is flex or socket system, first check GND connection of the PCB to the 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 them also.
(F) Also you can check all key anyone is short to line.
(G) sometimes keypad line breaks from CPU pin on PCB to the key panel, so check them.
2. Some key work and others do not work-
Some key work and some others is not working.For this type of problem-
(A) many a times this problem is form flex or socket system keypad. so check flex cable and socket all line,to know if any line is broken or not and need to change them and check all key connection on key panel.
(B) though its direct on PCB, if some of key line is broken internally.A maximum china phone have alternative test point near every key or with other keys on keypad. so check them with multimeter and although needs connection not to work with keys nearer to test point or other working key.
(C) common problem is keypad metal ball (which is short to line on key when we press) sometimes it damages when phone falls inside the water or over key voltage, so clean them or change it.
(D) also try to check the line continuously from CPU to the 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.
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(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 keys not working.
2. some keys works and some other not work.
3. sometimes work and sometimes not work.
1. All keys not work
China phone all key not work for this type of problem-
(A) though it is touch screen phone, first of all try to disconnect the touch panel line from the phone PCB or display flex (4 line)
(B) though not solve and keypad still direct on PCB, first you try to clean the PCB with cleaner.
(C) though not solve,now you try to format/flash your phone because sometimes key problem comes from software problem.
(D) If not still solved,check the CPU. 95% of china phone keypad is 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 then you can try to re-solder or charge the CPU.
(E)If it is flex or socket system, first check GND connection of the PCB to the 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 them also.
(F) Also you can check all key anyone is short to line.
(G) sometimes keypad line breaks from CPU pin on PCB to the key panel, so check them.
2. Some key work and others do not work-
Some key work and some others is not working.For this type of problem-
(A) many a times this problem is form flex or socket system keypad. so check flex cable and socket all line,to know if any line is broken or not and need to change them and check all key connection on key panel.
(B) though its direct on PCB, if some of key line is broken internally.A maximum china phone have alternative test point near every key or with other keys on keypad. so check them with multimeter and although needs connection not to work with keys nearer to test point or other working key.
(C) common problem is keypad metal ball (which is short to line on key when we press) sometimes it damages when phone falls inside the water or over key voltage, so clean them or change it.
(D) also try to check the line continuously from CPU to the 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.
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