Nokia has a two way system which means signal Transmite transmitting signal (TX) Received a signal receiving means (RX) Some parts are related here with TX and RX is as follows:

PA (Power Amplifier)

Power amplifier or power amplifier transmitting signal (Transmite Strength) is related here only thing it’s transmitting signal (TX) or well-Duplexer we call antenna switch. Combined between TX and RX which allows us to make calls in both directions simultaneously or together.
Occurrence of signal processing in and out. PA and Duplexer is a series that often lead to dead phone (shut down) when we'll make a call.

HAGAR
Including receiver or RX series of 75% and a transmitting / TX

COBBA
Including most of the circuit transmitting / TX relevant here: Strong transmit audio / sound is produced, which often leads to less loud hp. Including self-test from the main processor (CPU), so seing the service if contak damage.

Real Time Clock
As the name implies, where real-time process (run frequency accuracy) of damage to these parts will cause: The accuracy of speech or sound to be less precise (beat or slow tempo) The accuracy of power on and power down to be disrupted, causing the old HP is enabled or disabled.

CCONT
Is the part where the supply current is produced to flow into masing2 components. Damage to this part will cause the total dead HP.

FLASH IC
Is the part where the program generated data to govern the cpu do its work, especially here command signal receiving and transmitting. Damage to this Ic will cause: Contack service for self-test failed. Signal signal bar does not come out even though your name is. Booting failed total SHG die Hp
CPU (central processing unit)
Where all the commands executed by this part starting from the command transmitting or receiving signals. Damage to this part ways at times even difficult to detect. The entire process above will fail also related damage to this CPU.

Most damage and most annoying is the problem of signal. Any expensive phone with no signal is of no value. Also when carrying expensive mobile phone but the signal then the problem could be put to shame a problem.Sinyal tricky for all cell phone technician. Signal mostly identical to the PA or PA IC, even though not really a hundred percent. Signal problem has many links between one IC (components) with other components. In order to solve signal problems required some pre-requisite for any cell phone technician. Among them: The technician must have knowledge about the function of each component, the second, the technician must have a means test and repair equipment, and a third, a technician must have the ability or knowledge plus more, meaning the technician must be able to solve problems with different techniques.

There are Several kinds of signal problems, including:
1. Weak signal
2. Signal rise and fall
3. Signal at a particular location
4. Signal 5 seconds
5. No signal
6. 112 Signal only
7. Signal drop
8. False signal
9. Signal specific sim

Initial preparatory steps:
  1. Perform reset or return to the original settings, you can do through the menu and phone settings, then enter 12345.
  2. Perform only 112 calls or the network manually, when can the RF ICs are still in good condition.
  3. Perform software updates on your mobile phone. It could also downgrade if deemed necessary, and indeed the previous version was too high.
  4. Perform the test voltage on the PA components such as IC, RF IC, IC AUDIO, whether've got the right voltage.

If the initial step or the preparation we have done but the phone is still a problem it can be done according to the replacement of damaged components that experienced by the mobile device.
  • Signal weak, do change in IC PA, since these components functioned as an amplifier.
  • Signal rise and fall, can occur because VCO is weak, its reference function was neglected.
  • Signal at a particular location, change its IC PA, because the IC must be used not original, or the result of his replacement antenna.
  • Signal 5 seconds, damage to the IC CPU, because the phone can fall, but if not for the fall you can do flashing eeprom virgin, so that the phone was back to normal.
  • No Signal, the phone fell more damage to the IC Audio, converter function does not work.
  • Signal 112 only, a signal only from the RF IC, you can replace the PA because the IC is not functioning anymore.
  • Signal drop, because the IC is due to the PA, although IC PA itself still works but requires a very high currents at all, can reach 600 mA.
  • False signal, the indicator looks good and full, but could not make calls, more due to the antenna, connecting the disconnected function.
  • Signal certain sim, caused by the program or SW can be made clear SP Lock and could also be due to the replacement of the PA is not a precision IC or not IC PA original.