Micromax Q392 User manual

Q392 L3 Service Manual
1. Technical Specifications :
Particular
Remarks
Key Matrix For Flashing
N/A
Chipset
MTK6580 Quad-core
Android Version
Android L
Processor Frequency
1.3GHz
Network Mode
3G WIFI
ROM
8GB
RAM
2GB
Internal memory
5GB
Expandable Memory
32GB
Factory mode code
*#87#
Good Earpiece volume
32 ohm
Good Loudspeaker volume
4 ohm
Good Mic volume
2200 ohm
Good Vibrator volume
32 ohm
2. CAUTIONS
I. Flashing & Servicing must be undertaken by qualified personnel only.
II. Ensure all work is carried out at an anti-static workstation and that an anti-static wrist strap is
worn.
III. Use only approved Tools & components as specified in the parts list.
IV. Ensure all components, modules, screws, and insulators are correctly re-fitted after servicing
and alignment.

Q392 L3 Service Manual
V. Ensure all cables and wires are repositioned correctly if Handset disassembled
VI. Electrostatic discharge can easily damage the sensitive components of electronic products.
Therefore, Service Centre must adhere the precautions which mentioned above.
3. Q392 Level trouble shooting
1) Doesn’t Power On
Solution:
There is no current when the Power Key is pressed; check J1307 to see if there is false soldering, pseudo
soldering or damage, if yes, Carry out Resoldering or replacement;
There is no display when the Power Key is pressed, and the current stays within 100~120mA, if yes, The
problem is caused by pseudo soldering or damage of the MCP (U101);carry out repair soldering or replacement of the
MCP;
When the Power Key is pressed, the display freezes in a certain interface, if yes, Upgrade the software
version;
It should be caused by pseudo soldering or damage of PMIC(U401);
There is heavy current when the Power Key is pressed, if yes, Find the hot point, and replace the
corresponding material (PMIC (U401) and CPU (U101) are damaged in most cases.
Battery Connector

Q392 L3 Service Manual
2) Restart / Hang
When the Power Key is pressed, the display freezes in a certain interface, if yes, Upgrade the software
version;
There is no display when the Power Key is pressed, and the current stays within 100~120mA, if yes, The
problem is caused by pseudo soldering or damage of the MCP (U501);carry out repair soldering or replacement of the
MCP;
There is heavy current when the Power Key is pressed, if yes, Find the hot point, and replace the
corresponding material (PMIC (U401) and CPU (U101) are damaged in most cases).
3) LCD Issues “Black screen and no display of LCD”
Solution:
Exchange the front shell to judge if the LCD itself is abnormal, if yes, Replace the LCD;
Check if the LCD connector is damaged (such as burnout) , if yes, Replace the LCD connector XJ801;
Check if the diode D802 in the backlight circuit is soldered abnormally or damaged, if yes, Carry out repair
soldering or replacement of D802;
Check if the power inductor L801 in the backlight circuit is soldered abnormally or damaged, if yes, Carry
out repair soldering or replacement of L801;
Replace the backlight driver IC (U801).

Q392 L3 Service Manual
Display problems such as black screen, white screen and blurred screen when the backlight is OK.
Solution:
Exchange the front shell to judge if the LCD itself is abnormal, if yes, Replace the LCD;
Check if the LCD connector is damaged, if yes, Replace the LCD connector XJ801;
Check if the EMI components (EMI801, EMI802, EMI803,EMI804) connected in series on the LCD MIPI
signal line are soldered abnormally or damaged, if yes, Carry out repair soldering or replacement;
Replace U101.

Q392 L3 Service Manual
4) Touchpad Failure
Solution:
Exchange the front shell to judge if the TW itself is abnormal, if yes, Replace the front shell (with LCD);
Check if the LCD/TP connector is damaged, if yes, Replace the main LCD/TP connector XJ801;
Replace U101
Replace Touchpad
5) Proximity Sensor “Test failure of the light/proximity sensor”
Solution:
Check if the silicon case for light/proximity sensor is properly installed, if yes, Reinstall the silicon case for
light sensor ;
Check if the sensor have damage or pseudo soldering, if yes, Replace the sensor;
Check if the I2C pull-up resistors of the acceleration sensor are OK, if yes, Carry out repair soldering of
resistors R306 and R307;
Replace U101 .

Q392 L3 Service Manual
6) Accelerometer “Failure to realize automatic screen rotation during image viewing”
Solution:
Check if the voltages of C900（1.8V）and C901（2.8V）, respectively, if yes, Carry out repair soldering or
replacement;
Check if the IIC pull-up resistors R306 and R307 of the acceleration sensor have pseudo soldering, if yes,
Carry out repair soldering or replacement;
Replace U908.

Q392 L3 Service Manual
7) Keypad
There is no current when the Power Key is pressed, or volume keys do not work, please exchange the key
FPC;
Check if R401,R1324 andR1325 is soldered abnormally or damaged, if yes, Carry out repair soldering or
replacement of them;
Check if ESD component FV1320, FV1321 and FV1331 are soldered abnormally or damaged, if yes, Carry
out repair soldering or replacement of them;
Replace U101
8) Charging Failures “No indication during charging”
Solution:
Check if the charging IC D402 is abnormal, if yes, Carry out repair soldering or replacement;
Check if the pull-up resistors R304 and R305 of the charging IC are abnormal, if yes, Carry out repair
soldering or replacement;
Check if the problem is solved after replacement of the PMU U401, if yes, It is problem of the PMU U401;
Replace the U101.

Q392 L3 Service Manual
There is charging indication, but no charging current.
Solution:
Check if there is any obvious damage on the surface of the charging IC U902, if yes, The charging IC is
damaged; replace U902;
Replace L407 and R328.
9) USB “Failure of Connecting the Phone to the PC via the USB Data Cable”
Solution:
Check if the connector XJ103 is damaged or has pseudo soldering, if yes, Carry out repair soldering or
replacement of the material;
Check if D401, FV109,FV110 are abnormally soldered or damaged, if yes, Carry out repair soldering or
replacement of the TVS tubes;
Replace U101.
10) Main Camera “Photographing and Shooting Failures”
Solution:
Check if the camera is properly installed, if yes, Reinstall it;
Exchange the camera to see if the problem is solved, if yes, The problem is caused by the camera itself;
replace it;
Check if the camera connector has pseudo soldering or damage, if yes, Carry out repair soldering or
replacement of XJ701
Check if the IIC pull-up resistors R302 and R303 have pseudo soldering, if yes, Carry out repair soldering or
replacement of R302 and R303.
11) Front Camera “Photographing and Shooting Failures”
Solution:
Check if the camera is properly installed, if yes, Reinstall it;
Exchange the camera to see if the problem is solved, if yes, The problem is caused by the camera itself;
replace it;
Check if the camera connector has pseudo soldering or damage, if yes, Carry out repair soldering or
replacement of XJ702;
Check if the IIC pull-up resistors R302 and R303 have pseudo soldering, if yes, Carry out repair soldering or
replacement of R302 and R303.

Q392 L3 Service Manual
12) Flash Light “Malfunction of Torch or Flashlight”
Solution:
Check if the camera can be turned on, if yes, The problem is caused by the rear-facing camera; see the
analysis of camera failures;
Check if the light can turn on when battery voltage is supplied to its both ends, if yes, Replace the light
HL902;
Replace U700.
13) Vibrator Failures
Solution:
Check if the vibrator has pseudo soldering or damage, if yes, Carry out repair soldering or replacement;
Replace U401.

Q392 L3 Service Manual
14) Sim “Failure to identify SIM card”
Solution:
Check if the SIM card sockets J1301andJ1303 is obviously damaged, if yes, Replace the SIM card socket;
Check if the pins of the SIM card sockets J1301andJ1303 have pseudo soldering, if yes, Carry out repair
soldering;
Check if the ground impedance of each pin of the SIM card sockets (except the ground pin) is low (lower
than grade K) , if yes, Replace U401;
Replace U401
15) Network /GPS / WI-FI “Weak signals of main antenna and GPS and WIFI antennas”
Solution:
Check the surfaces of the main antenna and the GPS and WIFI antennas to see if there is any
crease or breakage;
Check the gold fingers of the main antenna and the GPS and WIFI antennas to see if there is
any breakage and if the gold fingers are in good contact;
First, it is needed to check the matching parts of the main antenna and the GPS and WIFI
antennas to see if there is pseudo soldering or missing part, and check if the cables and the
corresponding sockets are in good contact.