What's the reason that the millet 4s phone doesn't have a network signal?

No network signal solution for Millet 4s mobile phone

1, you are in the environment mobile phone signal is not good to the Internet (basement or subway station is particularly serious).

2, mobile phone software factors caused by the mobile phone can not be online, check whether GPRS open, or mobile phone restart, and sometimes restart the phone will solve the network is not connected to the problem.

3, if your phone is owed, pay after the restart of the mobile phone to restart the function of GPRS Internet. There is also a point, for the user does not open through the GPRS function to first call service provider service telephone line opened GPRS network can.

4, sometimes the security software because the mobile phone traffic is not enough to automatically turn off the Internet function, this also need to pay attention to

In the case of the phone and the menu of the network settings in the submenu, select the Search network, enter and then move the search network and then determine;
①: If you can find the network (China Mobile and Unicom will show on the screen) on the initial indication that the receiving part is working, not the network (no signal) fault is the launch part of the question
Problem (only show China Mobile or one of the Chinese unicom, it is only a mobile phone access to the partial channel is not smooth or 13 trillion/vco frequency offset, if the launch part of the normal will not not network);
②: If you can not search the network on the phone to receive the circuit part of the problem.
Initial location of faults in maintenance
Before opening the phone, we can connect the power supply to the power-on (do not put cards), observation of mobile phone search network current and standby current changes, usually five seconds after the start of the mobile phone's current changes in the range is relatively large, generally around 100mA irregular beating (at this time is the receiver of the mobile phone in the receiving State, Constantly change the frequency of the VCO, so that the frequency of phone reception
Frequency of the public channel on the base station).
①: If the receiving part of the work is normal, a few seconds the opportunity to enter the normal standby state, the current in the 5-20ma about a regular change (about a second swing), this time the mobile phone to answer
The receiving part is basically normal;
②: If the phone boot after the current is always in the 50-100ma around irregular changes, in about 10 seconds back to 10-20ma, and then a few seconds to jump to 50-100ma around, so repeated, then
Indicates that the receiving part is not working properly.
③ if the current in the boot after a motionless (no search action), that the network failure is a logical circuit out of the problem (generally mostly virtual welding or software problems).
For mobile phone does not network (no signal) fault can be divided into no receive and no launch two of cases.
㈠: No receive: (see there is no search current, the general search current in the 5~20ma between the bounce, there is a signal about a second swing once)
⑴: There is no network of search current: The fault occurred in the receiving front-end circuit (such as antenna switch, receive filter and one or two if filter), generally for the component virtual welding or damage.
⑵: There is a search current and the current in the 100-150ma constantly beating, this kind of fault occurs in the VCO abnormal and 13 trillion AFC abnormal, should focus on check these two parts and connected with the electricity
Lu.
⑶: No search current No network: The fault occurred in the logical part, generally for the CPU without output rx-on signal, audio IC rx-i/q No output, code chip, CPU virtual welding or software information does not
Yes, the power supply IC (Power supply pipe) is not able to supply the receiving circuit.
⑷: There is a search current but large (more than 200mA); The fault is generally occurring in the intermediate frequency IC and its connected components, can check if IC has no virtual welding or damage.
㈡: No launch: see if there is no emission current, can dial 112 test machine. Launch normal current about 200-300ma, and will fall back to 100-150ma to swing regularly (note: CDMA
, PHS do not swing).
⑴: There is a transmission current response and can not call, the specific performance: Dial 112 press the launch key when the current from standby current up to 100mA fixed for a period of time and then fell back to the electromechanical
Flow, this kind of fault is generally the launch of the final stage problems, should focus on the antenna switch (or road), emission filter, amplifier and other components, specific measures can be removed antenna switch and hair
Injection filter, directly with a small capacitor will be launched filter path connection, and then use two thin lines (about 10cm) respectively welded to the receiving front-end and transmit signal output, and then dial 112 test machine
, if you can make a phone call, it means that the antenna switch or emission filter has a problem; If you do not call, the current reaction and the same, at this time can be removed, and then use two fine
The line (about 10cm) is welded to the receiving front end and the transmitting signal output (the input end of the amplifier, the output of the VCO), then dial 112 test machine, if you can make a phone call, then the amplifier has asked
If you still can't make a phone call, you should focus on checking if IC and VCO.
⑵: No emission current, the specific performance is: Dial 112 press the launch key when the current does not change. This fault is generally in the logical part, generally the CPU has no output tx-on signal, audio
IC (CPU, if IC) no tx-l/q signal output), code piece (font) data is not correct, audio IC (CPU, if IC) virtual welding and so on. Each of the small parts can be inspected separately.
⑶: High or small emission current, specific performance: Dial 112 press the launch key, sometimes can be played, but the current is larger (above 400mA), or smaller (below 100mA), this
The situation generally check the power amplifier, the high-level (launch pre-amplification) tube is damaged.
⑷: There is a transmission current response and can not call, the specific performance: Dial 112 press the launch key when the current from standby current up to 100mA fixed for a period of time and then fell back to the electromechanical
Flow. Some should check the power control has no signal output, and then the right remedy.
The concrete detection method of the fault
㈠: For the receiving circuit, should focus on the detection of antenna switches, filters, 13 trillion AFC (should have about 1-1.5v jump), VCO voltage supply (generally 2.8V) and control voltage (should be
have about 1-2.8v jump), rx-i/q signal (some mobile phone is two, some mobile phone is four), rx-on signal (generally in the CPU output) and so on. Some of the machines also have separate high discharges.
Road (Nokia and Samsung, etc.), should also measure the quality of the high-voltage tube and the operating voltage is normal.
㈡: For the launch circuit, should focus on the inspection of antenna switches, filters, emission VCO has no control voltage and supply voltage (generally 2.8V), amplifier, tx-on signal (generally in the CPU
Output), audio IC (CPU, if IC) no tx-l/q signal output), the code piece (font) data is incorrect, audio IC (CPU, if IC) virtual welding, power control has no output signal (if
moto-v998 series is also to see whether there is negative pressure, and so on.
In the maintenance of cell phone does not access the network (no signal), if the use of Puy and frequency is more relaxed and accurate judgment (incidentally: spectrometer in the measurement of VCO can indeed be measured
VCO frequency, but because the mobile phone in the work of the receiving or firing frequency is not constant, it is by the base station randomly assigned to the mobile phone, so even if there is a frequency deviation can not be
Know, everyone in the maintenance should be rooted in the specific situation, do not think that there are high-frequency signal output to think that the VCO is all right, but most of the maintenance does not necessarily have these two instruments was walking my
, so for the introduction of the maintenance staff can be based on the above ideas in a step-by-line overhaul, while measuring rx-i/q, tx-i/q, rx-on, Txon and other signals, the available numbers
The table is measured to obtain a voltage jump (on a DC 2-20v), if you want to see some of the available pointer table (in the DC 5-10v file) to measure the above points of electrical signals. By measuring this
Some receive/transmit switch control signal and receive/transmit baseband signal, we can put the cell phone not to network (no signal) fault locked in the RF circuit or logic circuit, so receive/
The emission switch control signal and the receive/transmit baseband signal are also known as the watershed for testing the phone's not accessing the network (no signal).

The above is the cloud Habitat Community small partners for you to organize the problem of mobile phone signal is not good solution, I hope this tutorial can help you.