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
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)
Power ic and v+/b+ way
Last try is cpu.
To be continued....