Nokia Customer Care
Appendix A: RF Troubleshooting
A-66
Company Confidential
Copyright
©
2005 Nokia. All rights reserved
GSM1900:
Offset (kHz)
100
200
250
400
600
1 200
< 1 200
< 1 800
Limit (dBc)
+0,5 -30 -33 -60 -60 -60
One example of measured GSM Modulation Spectrum in EGSM900 band is presented in figure
"TX Modulation spectrum (GSM)".
•
If modulation spectrum is not as expected separate the phone into parts and place to the
module jig (
Notice that there are three antenna connectors in the module jig, one for GSM, one
for WCDMA and one for Bluetooth. Make sure that all connections are made to the correct RF-
connector
).
3.4.1 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. Check R7516 resistance value with an
ohmmeter and replace resistor if needed.
3.4.2 Does GSM PA (N7502) get correct bias currents? Is the level of bias currents ok?
EGSM: Icont_21 and Icont_22
GSM1800/GSM1900: Icont_31 and Icont_32
•
GSM transmitter has to be active before measurements. Procedure is explained in section
“Transmitter troubleshooting”.
•
Set TX power level to the maximum (“5” in EGSM900 and “0” in GSM1800/GSM1900)
•
Measurements can be done with an oscilloscope and a VOLTAGE probe.
•
EGSM900:
-
Connect the probe to C7545 or C7544. Notice: C7544 is a non-assembled component so the probe
should be connected to the pad that can be still found from the PWB
-
Typical full TX power bias currents (Icont_21 and Icont_22) should look somehow similar to figure
Icont_21/Icont_22 (DC Offset 1.2 V)”, when measured with an oscilloscope and a probe.
Check both currents.
•
GSM1800 or GSM1900:
-
Connect the probe to C7561 or C7556. Notice: C7556 is a non-assembled component so the probe
should be connected to the pad that can be still found from the PWB
Typical full TX power bias currents (Icont_31 and Icont_32) should look somehow similar to figure
6.5.5 "Icont_31/Icont_32 (DC Offset 1.2 V)"
when measured with an oscilloscope and a probe. Check
