Nokia 8850 mobile phone , with its luxurious , glamorous , elegant and family favorite to win playing machine , but " rich girl " Sometimes to make in cases of sexual , maintenance staff really made us a headache , I almost lost this time depriving machine . One day, a Nokia 8850 for repair , the customer said he had long ago dropped the phone 8850 underground , now call displays are normal, but there have been several times when no display problems , asked me to check. I say another monitor on it, he said now displayed properly , check the check did not say how bad the display . So I tested a bit disassemble the display interface voltage , told him, or want to change the display , he asked me how much money I have to say for a $ XX . He did not call me back in change machine to him. We all know that 8850 phone's display is very delicate , as long as the phone previously appeared outdated and sometimes no display problems , a teardown , sometimes no matter how you dress how to change conductive adhesive will no display , more "dangerous ", which is why I the reason he started going to change screens . I'm sure this one is no exception , and finally persuaded the owner to change a display. Installed machine , test machine everything is normal to him. After about ten minutes apart can master the machine back to repair bad for me his cell phone , the phone call does not go into the fight too , want me to lose machine . I took a look , very strange signal full grid , but unstable , Nokia 's built-in antenna cell phone signal instability is normal, but the phone will not cause difficulties . I have to convince him to the ground Sunday, the network is busy stay Chaxiu the machine , and promised to pay him a bad repair the 8850 phone. Customers gone, I meditate for half an hour , then tried to call several times with the fault plane , the phone displays "Call " and then returned to " China Telecom" , the phone beside the phone , dial the phone using the telephone , the telephone handset acoustic emission interference when the phone there , but only a few will calm down , and then they hear " you dialed is not yet turned on ." My analysis: the signal is just full grid instability, call the " call " appears , answer the phone interference Boeing , cell phone reception , transmit start control, frequency synthesizer circuit , 13MHz frequency aspects should be no problem , where is the problem ? Is a software problem ? Network problem? Should not. So the end of the circuit should be fired appear problem? In order to confirm your own ideas, memories of the previous one I re Motorola T2688 no network failure "special case " examples of successful repair . I was a card test machine , T2688 manual search network can not be found to the network , call about "112" , "No contact ." Motorola T2688 mobile phone to dial "112" appears "impermissible " and should be receiving circuit problem , if a " no contact " is a transmission circuit failure, so I start with the launch investigation since the end of the amplifier circuit . After disassemble find audio IC, IF amplifier workers have been replaced , I re- applied after the amp welding look down, thorough cleaning treatment . The amplifier U201 4 feet to a wire as an antenna , it is worth noting that not shorted to ground , the card search network " China Mobile" displayed, reinstall the power amplifier , the test machine was found less than a network. The efficacy of U201 and then a 10- foot wire test machine , " China Mobile " is displayed , the fault should C205, L201 and U501 at the antenna switch , upon inspection , the antenna switch U5Ol partially damaged at the fly line from U201 to L503 C501 installed with intermediate troubleshooting . Nokia 8850 receives the front end of the circuit with the launch of Motorola T2688 transmitter receiver front end of the circuit are different, but both DCS and GSM transceiver switching frequency via FireWire switch segment , the principle is largely the same , but there is a big line T2688 switch control IC , while the Nokia 8850 antenna switch controlled by the IF IC N505. Dial 8850 from fixed phones interfere with the sound of machine fault analysis , the effect of the 8850 should not be a problem . So multimeter test antenna switch 2670 , is part of a bad antenna switch from C743 fly line to Z670 at 12 feet , installed a try solve the problem. Z670 This antenna switch , and some also called diplexer circuit in the mobile phone is widely used, it is a cell phone signal to cross the checkpoint , damage or Weld easy to make and sometimes no network or signal instability occurs when the phone or launch difficult to fault . The circuit is made of ceramic filters. Diodes, capacitors and the like.

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