Nokia RM-57 Service Manual page 246

Appendix A: RF Troubleshooting
• Typical TX control voltage TXC levels should be now about:
GSM850/EGSM900: 1.0 V while TX burst and 0 V otherwise.
-
GSM1800/GSM1900: 0.7 V while TX burst and 0 V otherwise.
-
3.1.1.1.9.1 R7514 in place?
• Check that the component is in place and solder joints are ok
• Disconnect the power supply from the phone and check R7514 resistance value with an
ohmmeter
3.1.1.1.9.2 C7549 working correctly?
• Check that the component is in place and solder joints are ok
Disconnect the power supply from the phone and use an ohmmeter to check that C7549is not
•
short-circuited. If short-circuit is found replace the capacitor.
3.1.1.1.9.3 Retu ok?
3.1.1.1.10 VCTCXO frequency and output level correct?
• Measurement can be done with an oscilloscope and a probe.
• Connect the probe to C7529 (or C7582)
• The frequency of the VCTCXO should be quite exactly 38.4 MHz and level about 0.5 - 0.9 Vpp.
Example of the correct VCTCXO output signal is presented in figure
Offset 1.24
3.1.1.1.10.1 VXO-voltage ok? (=Vdig).
• Measurement can be done with an oscilloscope and a probe
Connect the probe to C7560 (or C7526, C7513)
•
• VXO-voltage should be about 2.5 V
3.1.1.1.10.1.1 C7560, C7513, C7526 and C2214 ok?
• Check that components are in place and solder joints are ok
• Disconnect the power supply from the phone and use an ohmmeter to find out if the VXO-line
is short-circuited to the ground. If short-circuit is found replace C7560, C7513, C7526 and
C2214. If replacing does not help then go to the next steps.
3.1.1.1.10.1.2 Replace Retu
3.1.1.1.10.1.3 Replace Hinku (N7500) or Vinku (N7501) or VCTCXO (G7501) or all three components
3.1.1.1.10.2 BB AFC-voltage ok?
A-28
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4.6.1. "VCTCXO Output (DC