Page 263 - CITS - Electronic Mechanic - TT - 2024

ELECTRONICS MECHANIC - CITS

3 Reball the ICs, resistors, capacitors and diodes by placing them on a BGA Reballing Station. Press down
firmly onto the solder balls with your fingers and apply power. The ICs, resistors, capacitors or diodes should
be tested for operation and then returned to the PCB.
4 Using tweezers or forceps, place the new BGA ICs, resistors, capacitors or diodes onto the solder balls. The
BGA chips are placed directly onto the solder balls or on top of a new substrate. Once in place they should be
pressed down firmly and then power applied again.
5 Wipe away any excess solder paste with a sponge using Acetone or Isopropyl Alcohol. Remove any excess
liquid with a cloth and allow to dry.
6 Using a magnifying glass, check the solder balls for solder bridges. If you find any then they should be
removed with a solder wick.
7 The final step is to use a multimeter to test all of the new components and make sure that they are functioning
properly.
Concept of power failure of mobile phone and process to solve it (dead handsets)
A Dead mobile phone is a hand set that does not get switched ON.
How Does a Mobile Cell Phone Gets Dead
If the mobile phone gets dropped down on the floor or on some hard surface.
If the mobile phone gets wet or is dropped in rain or water.
Mobile Cell Phone Dead Problem and Solution – How to Repair a Dead Mobile Cell Phone
Remove the battery and see if it gets charged or not. Check voltage using a Multimeter. Voltage must be above
3.7 Volt. Use a Battery Booster to Boost the Power of the Battery and Charge it again.
Check Battery Point and Battery Connector. Clean Battery Point and Battery Connector to remove any carbon
deposits.
Resold or change the Battery Connector.
Insert charger and se if the “Battery Charging” appears on not. If there is icon of “Battery Charging” but the mobile
phone does not gets switched ON then check ON / OFF Switch. Voltage of ON / OFF Switch must be 2.5 to 3.5
Volt (DC). Clean or change the ON / OFF Switch. Check track of ON / OFF Switch and Jumper if required.
If the charging icon is not there then check voltage of ON / OFF Switch. If the voltage is between 2.5 to 3.7 Volts
DC, then RELOAD Software in the Phone (Software Flashing).
If the phone does not gets switched ON even after reloading software then Heat the C.P.U, Power IC and Flash
IC.
If there is no voltage on the ON / OFF Switch then check track of the ON / OFF Switch. Jumper if required.
If the problem is not solved then heat, Reball or change the Power IC and CPU to fix the problem.
Keep the Multimeter on Buzzer Mode and Check +_ and – of the Battery Connector. If there is Buzzer Sound then
the Set is short. If there is short at the Battery Connector then clean the PCB with thinner. Heat the PCB.
If this does not fix the set dead problem then remove the PFO and check for short. If there is short then replace
the PFO.
Remove the charging connector and check for shorting. If there is short then change the connector.
Remove the charging IC and check for shorting. Change if required.
Remove the Bluetooth IC and check for shorting. Replace if required.
Remove the Power IC and check for shorting. Replace with a new one if required.
Remove the CPU and check for shorting. Replace if required.
Remove all the Big Electrolytic Capacitors and check one by one. Replace capacitors if required.
Note:
Some mobile phones get dead if the RTC (Real Time Clock) is faulty. This happens mostly in China
Mobile Phones. Change the RTC to fix the problem.
If the mobile phone gets hang after reloading software then change the RTC.
If the set is still dead then check by replacing the 26 MHz Crystal Oscillator.

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CITS : E & H - Electronics Mechanic - Lesson 130 - 145