Nokia RM-57 Service Manual page 254

Appendix A: RF Troubleshooting
• Connect the probe to C7549
• Typical TX control voltage TXC timing should look somehow similar to figure 4.6.2
mode (DC offset 0
roughly:
GSM850/EGSM900: 1.8 V while TX burst and 0 V otherwise.
-
GSM1800/GSM1900: 1.8 V while TX burst and 0 V otherwise.
-
• Change the TX to the minimum power level ("19" in EGSM and "15" in GSM1800/GSM1900)
• 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.
3.1.2.1.4.1 R7514 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 R514 resistance value with an
ohmmeter
3.1.2.1.4.2 C7549 working correctly?
• Check that the component is in place and solder joints are ok
• Disconnect the power supply from the phone and check with an ohmmeter that C7549 is not
short-circuited.
3.1.2.1.4.3 Retu ok?
3.1.2.1.5 Does GSM PA (N7502) get correct DET_SW_G -voltage from Vinku ASIC (N7501)?
GSM transmitter has to be active before DET_SW_G voltage can be measured. Procedure is
•
explained in section "Transmitter troubleshooting".
• Measurement can be done with an oscilloscope and a probe.
• Connect the probe to C7595 pad. Notice: C7595 is a non-assembled component so the probe
should be connected to the pad that can be still found from the PWB.
• DET_SW_G voltage should be about 2.8 V while TX burst and 0 V otherwise.
3.1.2.1.5.1 Replace Vinku (N7501)
3.1.2.1.6 Are components in GSM power control loop in place and working ok?
R7516 and C7559
• Disconnect the power supply from the phone and use an ohmmeter to check that C7559 is
not short-circuited. If short-circuit is found replace the capacitor.
A-36
V)" (GSM850/EGSM900 TX power level 5) and voltage levels should be
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"TXC in GSM