xiaolabaDIY 的部落格

 

如今的手機, 已經夠便宜, 電訊服務營運商同電話製造商都會採用所謂的策略聯盟的方法, 即係如果你綁約某個年期, 現在急於推出市場的新款手機就會由原價XXXXX, 優惠給消費者以XXXX購買, 比較舊款的手機, 甚至有所謂的0機價. 試問世界上有人在做賠本的生意嗎?!

銷售策略, 0機價, 綁約........到底還是要做生意, 要賺錢. 因此通常手機有咩問題, 先進國家D人都係放棄然後再買部新機, 舊的手機就會被販賣到經濟還在開發中的地區, 以前在大陸就看到很多很多這樣的機器. 現在中國本身已經有好幾家大的電話製造商, 印度也被知名的電話製造商們定位成必爭之地, 目標是低價手機的戰場. 阿婆話, 個 NOKIA 8250 無法充電, 第一個問題, 係咪電池壞, 第二個問題係有無得整, 第三個問題係使吾使買部新機................

 

the dead unit, battery was empty and the phone is not be able to charge

 

un-cover the housings & un-screw the 6 screws, visual the inside of this Noika 8250

 

seperate the back housing, visual the module & key pad

 

flip the module up side down, visual the PCB and electronics components

 

locate the input circuitry for batery charging, the C-capacitor, Fuse & resistor. In general, the following should be the service condition
1) C is used to filtering the ripple of input voltage across the power rail, DMM measurement will give more than Maga-Ohm (10^6);
2) Fuse is used for over current protection, DMM measurement will gives about 0 Ohm;
3) R will has 0 Ohm or some lower reading;

However, this dead cell phone has her different representation about those 3 components,/
1) C has about 5 Ohm, almost short circuit
2) Fuse is opened without 0 Ohm

The readings above are able to tell very clear for the protection circuit of this cell phone, it experienced excessive charging voltage from charger or other power input. The fuse had fired as the C was in short circuit to drain the excessive current from the charger. It was possible the over charging voltage has been applied across the power rail, it breaks the Capacitor down as results a low Ohm resistor across the power rail. This very low Ohm resistor is able to short the power to ground, massive current flow through the fuse until the fuse fired. you can find the simple sketch here for the description aforementioned, http://hk.myblog.yahoo.com/xiao-laba/photo?pid=952&fid=2

 

No SMT fuse, only be able to savalage some SMT components from a scarp PCB out of desk phone without known value, but the SMT cpmponent will give limited tolerance once the component size is fixed. A diode and a capacitor had been selected to bring the dead cell phone back to alive. The fuse is no longer in place, just a subsitutation with solder joint, not a bad deal if this dead phone can be fixed without buying a new phone.

 

return every piece back to the assembled condition, insert the battery with couple minutes charge, this Nokia 8250 is able to power up again. of course, the time & date has to be initialised again as long enough power loss without backup memory for the real time clock inside.

 

one or two more seconds, this Nokia 8250 is giving her charing condition again, the power is flowing from the charger and stroing to the battery again. It works, the basis remains no change with power supply design for circuit protection, this dead unit can be fixed with simple enough approach, of course, the cell phone supplier may bot be happy to see extended service life without contribution to the sales record if no buying a new cell phone by today.

-end