The first part of the handling ideas for various faults of mobile phones
Ideas for dealing with various faults of mobile phones
- It can't be turned on
Let's take a look at the processing processes that need to be gone through for normal boot: press the boot button → boot command to send the power IC module → the control foot of the power IC to get the signal→ power IC works → CPU; The 13MHz master clock is powered on→ CPU reset and the initialization program is completed→ CPU sends a poweron signal to the power IC block→ power IC stably outputs the working voltage required for each unit→ the mobile phone is successfully turned on, and then enters the network access search and registration stage. According to the processing process of start-up, we can analyze the inspection and treatment of the following relevant parts:
Due to the frequent use of the power button of the mobile phone, is this button not in good contact?
.Is the power IC module soldered or burned out? Due to the large operating current of this IC, it has a high probability of failure.
Does the power IC have a boot signal sent to the CPU?
A certain load of the power supply IC has serious leakage or short circuit, resulting in a large start-up current, so the protection shutdown. A common point of failure is the burning of the MOS switch tube of the PA or PA.
. CPU corresponding pin soldering? This is a common point of failure.
. Whether the three basic conditions for the normal operation of the CPU are met: (a) the working voltage of 3V; (b) 13MHz clock; (c) Reset circuit.
. Does the CPU output a poweron signal to the power IC?
Is there an error in the initialization software? Try rewriting the software.
(Note: When checking for such faults, the artificial fault unit separation method can be used, that is, the artificial jumper method (a short thin enameled wire can be used) to add a voltage to the poweron pin of the power supply IC, if each power supply IC can output a normal voltage at this time, the fault point is generally in the CPU control part or software, and the fault point is in the power IC part or its load.) When checking for faults, you can check from front to back according to the direction of the signal processing process, or you can check from back to front, or you can start checking from somewhere in the middle, depending on the specific situation and the mobile phone model. )
- It can be turned on and off, but it cannot be registered in the geographical area where the signal strength of the base station is sufficient
This fault is also one of the common ones. It involves a large number of units. This type of failure occurs when there is a problem with the reception, transmission, synthesizer, BB processing, CPU, and software.
Inspection & Treatment:
Is the antenna in good contact? Treatment: Clean with anhydrous alcohol and correct the antenna reed.
Check the operating voltage of RF and IF synthesizers, RFVCO, IFVCO? Is there a virtual weld?
.Check the LNA (Low Noise Amplifier) operating point on the receive front-end? Is there a virtual solder?
Check whether the performance of RFSAW or IFSAW has deteriorated? Is there a virtual solder? You can use 100P capacitor jumper to try it.
Check the working voltage of the RFIC? Is there a virtual solder?
Check whether the working voltage of the I/Q quadrature MODEM is normal? The general normal value is: DC1.2V, single-ended AC500mVpp.
Check the working voltage of the BB processing unit? Is there a virtual solder?
Check whether there is any problem with the transmitter VCO, PA, MOS switch and APC control circuit? Is there a virtual solder? This is a typical point of failure.
For earlier models, do you still need to check whether the connector between RF and BB is soldered?
Repair the CPU and rewrite the software.
- After inserting the SIM card, the SIM card is still not detected by the mobile phone
Failure Analysis:
(1) Because the contact point area of the device in the mobile phone is very small and the contact pressure is not too large, and the structural design of some mobile phone SIM card holders is not reasonable enough, it is easy to have this kind of failure.
(2) At present, the SIM card has both 5V card and 3V card, which involves the conversion of a SIM card power supply, and also needs to have a boost circuit from 3V to 5V.
Inspection & Treatment:
(1) Are the reeds of the SIM card in good contact? If there is a problem, you can clean or carefully correct the SIM card reeds;
(2) Is the SIM card's operating voltage or boost circuit normal?
(3) Is there any problem with the SIM-related detection and control circuit? In particular, is there any virtual soldering?
(4) If there is an error in the software data or part of the data is lost, can I write the software again to try it?
Fourth, the signal is sometimes good and sometimes bad
Failure Analysis:
In the case of battery failure and external environmental interference, the cause of the fault may be the presence of virtual solder joints inside the phone (especially for the phone that has been bumped, crushed, or dropped), or it may be a problem with the software.
Inspection & Treatment:
According to the fault phenomenon, you can repair and clean the relevant circuit parts once (the key inspection parts are the antenna, transmitting channel, receiving channel, frequency synthesizer), and then carefully install the mobile phone, if the mobile phone can work normally and stably for half a month (referring to the conditions of different times and places, the fault does not appear once), it means that the fault has been eliminated, otherwise, the fault point still exists.
This kind of fault is called a "soft fault" in the repair of household appliances, and its elimination is sometimes very "tricky", which requires the repairer's rich experience, meticulous and comprehensive analysis.
Fifth, the working or standby time is significantly shorter
Failure Analysis:
This failure can occur due to:
(1) The battery is not fully charged, the quality deteriorates, and the capacity decreases;
(2) There is a problem with the PA part, and the emission efficiency decreases, which leads to an increase in power consumption;
(3) There is a leakage fault in the machine, especially for a mobile phone that has been immersed in water.
By measuring the working current, standby current, and shutdown current of the mobile phone, you can determine whether the problem is in the battery or the mobile phone.
- The other party can't hear the sound or the voice is low
Failure Analysis:
Because the connection between the microphone (microphone) and the PCB in the mobile phone is almost all non-permanent mechanical connection, the area of the contact reed is relatively small, and the mobile phone is a mobile product used outdoors, so it is easy to produce the fault of poor contact of the microphone.
Inspection & Treatment:
(1) Is the transmitter in poor contact? Treatment: Calibrate or clean the reeds.
(2) Is the static DC bias voltage of the electret microphone normal? (Generally 1.5~2V)
(3) Microphone quality problems. It can be measured with the 20kΩ resistance of the digital triple meter in the event of a power failure. When speaking into the microphone at close range and not speaking, the resistance value at both ends of the normal microphone should change significantly. If there is little or no variation, the microphone is of poor quality or damaged. Another way to check is to measure the voltage at both ends of the microphone with the AC file of an oscilloscope or triple meter when the call is in the state of the call, if the voltage is normal, it means that the problem lies in the voice processing part later.
(4) BB processes whether there is a problem with the source part of the IC (e.g., programmable audio preamplifier, A/D converter). Typical faults are incorrect working voltages or virtual soldering in the relevant parts.
(5) Is the microphone hole blocked?
- There is no sound or low sound in the receiver (earphone).
Inspection & Treatment:
(1) Is the volume set in the menu correct?
(2) Is there a problem with the headphones? Normal headphones have a DC resistance of about 30Ω and can hear "gurgle" when measured with a triple. Sound (the headphones in mobile phones generally use dynamic type, and a few use piezoelectric type).
(3) Is the contact between the headphone reed and the PCB good? The treatment method is the same as above.
(4) Is the headphone audio amplifier not working properly or is there a virtual soldering in the related circuitry?
(5) Is the receiver hole blocked?
- No ringing or low ringing sound
Inspection & Treatment:
(1) Is the contact between the ringer and the PCB good? The treatment method is the same as above.
(2) Is the ringer damaged (the normal resistance value is about 30Ω for the moving coil type) or is there a virtual solder in the related circuit?
(3) The drive transistor burns out?
(4) Is the sound hole blocked?
- The LCD display is abnormal
Inspection & Treatment:
(1) Is the coupling between the LCD and the PCB in good contact? It can be cleaned and then installed to try it.
(2) Is the working voltage and clock normal? Is there a virtual weld?
(3) Is there a problem with the software? You can write the software again and try it:
(4) Is the LCD quality poor? Replace the LCD.
