Nokia RM-57 Service Manual page 253

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3.1.2.1.2.1.1.1.2 Replace Vinku (N7501) or Hinku (N7500) or both
3.1.2.1.2.1.2 R7521 and R7504 in place and working correctly?
• Check that components are in place and solder joints are ok
• Disconnect the power supply from the phone and check R7521 and R7504 resistance values
with an ohmmeter.
3.1.2.1.2.1.3 VB_EXT voltage ok?
• Measurement can be done with an oscilloscope and a probe.
Connect the probe to C7518.
•
• VB_EXT voltage should be 1.325 – 1.375 V. Typical value is 1.35 V.
3.1.2.1.2.1.3.1 Is R7503 in place and working correctly?
• Check that the component is in place and solder joints are ok
• Disconnect the power supply from the phone and check R7503 resistance value with an
ohmmeter
3.1.2.1.2.1.3.2 Capacitors C7518, C7520 and C7570 working correctly?
Check that components are in place and solder joints are ok
•
• Disconnect the power supply from the phone and use an ohmmeter to check that capacitors
are not short-circuited. If short-circuit is found replace capacitors mentioned above. If this
does not help go to the next step.
3.1.2.1.2.1.3.3 Replace Vinku (N7501) or Hinku (N7500) or both
3.1.2.1.2.2 Replace Vinku (N7501)
3.1.2.1.3 Are TX-IQ signal waveforms looking correct?
• These current mode signals are not possible to measure, but are tested with self-tests. So if
there is no fail in 2.3
or RAP3G (D2800) is faulty. Notice that it is not possible to replace RAP3G ASIC.
3.1.2.1.4 Is the TXC-signal coming to Vinku ASIC (N7501) OK? Is signal level correct?
• GSM transmitter has to be active before TX control voltage TXC can be measured. Procedure is
explained in section "Transmitter troubleshooting".
• Set TX power level first to the maximum ("5" in GSM850/EGSM900 and "0" in
GSM1800/GSM1900)
• Measurement can be done with an oscilloscope and a probe.
ST_CDSP_TX_IQ_TEST
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Appendix A: RF Troubleshooting
these signals should be ok. Otherwise Vinku (N7501)
A-35