A27 Service Manual
Contents
1. 17 SLE pci eu oie 18 3 12 BINGO OC TAU assess e a etii e E ER PEE QUERER EE FEE ACE IHE AEREE 19 DPA ING SIG Mal H 20 3 15 Failure to identify T flash card c eee ee eee eere reete ee eene een 21 3 16 Earphone fauli yr erre oS FERE UY PET SE Y FERES FERRE YE FERE EE ERU RT POPE CERE PEEUS 22 3 17 Unable to use USB aeccoc d mie n EREH EXE UA Hobo D sissoo sosi QUE ENTE Ras 23 cromax nothing like anything 1 Circuit diagram instruction 1 Main board explored view direction sensor RF amplifier receiving filter SC6820 T card connector Battery connector J RF transceiver Earphone connector TP connector MU UUW cromax nothing like anything 1 2 Detailed Description of Circuit Chart 1 3 RF circuit This phone is designed on SC6820 platform RF main chip integration SR1019 PA use RDA6163A TCXO uses 26MHz crystal oscillator 1 Receiving circuit The GSM or DCS signal received from a base station via antenna is inputted from the pin 27 of U101 send U104 U105 to pin A20 B20 A19 B19 This chip integrates LNA and Frequency mixer The signals are amplified by their own low noise amplifier LNA The amplified signal is sent to a down converter where the signal is mixed with local oscillation LO output from RX VCO to generate zero i2. is i i Si I wp o4 uL Ks NE Sz rei m Wr at sas n e 7 a 7 1a MTT TIT 2 Fault maintenance Note The PCBA repairing is a very important work during the final production of cellular phones The speed and quality of repairing decides the yield and production efficiency The repair idea is very important for a good repairing technician Make sure not to heat a board right away once a phone reaches at hand Cr Omax nothing like anything cromax 3 Trouble shooting and flow chart 3 1 Unable to power on the handset Failure to power on heck battery mounted correctly amp battery voltage gt 3 4V Re mount battery or Me replace battery heck if Keyboard backligh can be lighted No Check if LCD is connected correctly Pay attention to retain the calibration data Download software Ok Yes Solder or replace LCD Replace new mainboard Yes 3 2 No ring tone No ringtone Check soldering o speaker OK Check the speaker circuit no short ciruit or open circuit Yes Replace new mainboard Solder speaker OK Mark the failed speaker No Mark the mainboard with analysis result cromax nothing like anything cromax nothing like anythi
3. No gt Replace new receiver Yes gt Solder receiver connector Yes gt Mark the mainboard with analysis result cromax nothing like anything 3 10 Vibrate fault Vibrator fault or No vibration A Is vibrator soldered well No Solder vibrator or replace vibrator Check Wire of vibrator int broken Yes gt Replace vibrator Check vibrator circuit Mark the mainboard with M ae No gt o short circuit or open circu analysis result Replace new mainboard 17 cromax nothing like anything 3 11 FM fault Failure to open FM or FM can tscan any station Software version is correct No gt Re download software arphone can be detected and audio output is ok Bem ep arpan Yes Check FM circuit o short circuit or open circuj Mark the mainboard with analysis result No gt Yes Replace new mainboard 18 cromax nothing like anything 3 12 Bluetooth fault Bluetooth can t work Software version is correct No gt _Re download software Yes Is BT antenna assembled correctly No gt Re assemble BT antenna Yes Check BT circuit o short circuit or open circui Mark the mainboard with analysis result No gt Yes Repla
4. ce new mainboard 19 cromax nothing like anything 3 14 No signal No RF signal No gt Re assemble BT anntena Is RF antenna assembled correctly Yes Is the phone set into Flying indes Yes Return to Normal mode No Mark the mainboard with analysis result Check RF circuit for any fault Yes gt No Replace new mainboard 20 cromax nothing like anything 3 15 Failure to identify T flash card Failure to read T flash card Is T flash card inserted correctly No gt Re insert T flash card Yes Check the T flash card is ok No gt Replace new card Yes Check card socket is clean and no physical fault Clean socket or replace socket No gt Yes Mark the mainboard with analysis result Yes gt Check card circuit for any fault Replace new mainboard 21 Cr Om wax nothing like anything 3 16 Earphone fault Failure to use earphone Check earphone is ok No damage No gt Replace new earphone Yes heck earphone connector for soldering defect Yes gt Solder earphone connector Is there any foreign matter in earphone connector Yes gt Clean or replace connector Mark the mainboard with analysis result Check earphone ci
5. cromax nothing like anything A27 Service Manual Cr OImmax nothing like anything Table of Contents 1 Circuit diagram instruction eec ec eet obe NH HR ERREUR CREME SNR EE REN L YE XC N INR ANN UKR S dS 3 1 1 Main board explored view sesso es sete tuens td ento o 21e cra xi eo sa dea eaa pd sehen tP2 ie 3 1 2 Detailed Description of Circuit Chart 4 eeee ecce eee eee ee eee nne 4 1 3 R circuit m 4 TA Base Wat CCUG em 5 1 5 F n tion CACHE TET 5 PM Suri Wm 6 3 Trouble shooting and How Chart ossisescissscccecassseccecanccsecsancsceseuacedscsantasecnnncesucssacasecs 8 3 1 Unable to power on the handset ccce eee eese eere eee ee eee teen eee nae 8 3 2 ING TINO TONE uci sona esce v Deu ibd E CUL ERE ECXRATAN 0 ER HU I EOM odisse bebas GE ERU Thx AE EET D ssassn 9 3 3 LCD display fault eesssen eost erae rho asp PyY PER FERP EYES PEE CEPR OP EE YS M tesos svisa 10 3 4 Charing Fea e 11 3 5 Cam ra TAU 12 3 6 Fail to identify SIM card eeessoessoessocessecssocesooescosesscsssccesocesoossscessseessocesosseo 13 ST WV PAGE e E E E T E E TEE 14 3 8 Keypad falt C 15 3 9 Receiver rii M 16 3 10 Vibrate fault
6. k SIM connector for soldering defect Check SIM circuit for fault Replace new mainboard 13 cromax nothing like anything No Reinsert or change new SIM card Yes gt Solder or replace SIM connector Yess Mark the mainboard with analysis result cromax nothing like anything 3 7 MIC fault Unable to record No sound in microphone Solder or replace new Check mic for soldering defect micphone Yes Check if mic sound hole is jammed Clean mic sound hole and re assemble mic Yes gt Mark the mainboard with Check mic circuit for fault analysis result Yes gt Replace new mainboard 14 cromax nothing like anything 3 8 Keypad fault Keypad doesn t work correctly Check DOME is pasted and keymat is assembled correctly Paste the DOME or assemble keymat again Yes gt Is there any dirty on keypad Clean keypad surface and Yes gt surface test No i eee ewe Yes Solder or replace sidekey No short circuit Replace new mainboard 15 3 9 Receiver fault No voice in receiver Is receiver ok No broken wire Yes Check receiver connector for soldering defect Check receiver circuit for any fault Replace new mainboard 16 cromax nothing like anything
7. ng 3 3 LCD display fault Abnormal LCD Display Check If the lcd is damaged Yes gt Replace new LCD Check if the lcd connector is soldered sell No 3 Solder the lcd connector Yes Check If the LCD is mounted inverse Yes gt Re mount the lcd Replace the new mainboard 10 cromax nothing like anything 3 4 Charging fault Failure to Charge Check charger or Replace new charger Yes Replace new Charger Check battery is good or not No gt Replace new battery Yes Check charger connector for soldering defect Yes gt Solder charger connector Check charging circuit of mainboard for fault Mark the mainboard with analysis result Yes gt Replace new mainboard 11 3 5 Camera fault Failure to use camera Check camera for damage heck if camera is soldered or assembled well Check camera circuit for fault Replace new mainboard 12 cromax nothing like anything Yes gt Replace new camera Solder camera connector or Re assemble camera Yes gt Mark the mainboard with analysis result Yes gt 3 6 Fail to identify SIM card Failure to identify SIM card heck if SIM card is inserted correctly According to insertion direction Chec
8. ntermediate frequency ZIF signals The zero IF signal passes through a filter and is amplified by programmable gain amplifier PGA then the signal is outputted to I and Q demodulator to generate I Q base band signals 2 Transmitting circuit A transmitter consists of I Q modulation circuit up conversion mixer circuit 4 cromax nothing like anything power amplifier and duplex switch The I Q signal is inputted to be performed signal modulation as the modulation signal The modulated TXIF signals restrain its third harmonic by harmonic suppression filter The follow up TXIF signal will be sent to a discriminator on the offset frequency phase lock loop OPLL Then perform frequency discrimination to this signal and the mixed signal of TXVCO signal and RFVCO output signal The discriminator outputs the signal control RFVCO and RFVCO phase is enabled to lock at the phase of TXIF signal TXVCO output RF is still decided by RFVCO frequency The phases of RFVCO and IFVCO signals lock at the phase of VCTXO reference signal TXVCO output signal is sent to emission power amplifier PA A17 A16 pin to amplify The TX signal outputted by PA pin 27is transmitted to the antenna via antenna switch to launch 1 4 Base band circuit Base band main chip adopts SC6820 chip 1 5 Function circuit LODOS A E XY NC voc wao eume pem ier A SIM card cromax nothing like anything m ri 73 A uem
9. rcuit for any fault Yes Replace new mainboard 22 cromax nothing like anything 3 17 Unable to use USB Uable to use USB heck USB cable is ok no pin of aa ahi a No gt Replace new USB cable Yes Check if USB connector is solder ok no short circuit Solder or replace USB connector No gt Yes Replace new mainboard END 23
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