Appendix A: RF Troubleshooting
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A-69
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Change the TX to the minimum power level (“19” in EGSM and “15” in GSM1800/GSM1900)
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Typical TX control voltage TXC levels should be now about:
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EGSM900: 1.0 V while TX burst and 0 V otherwise.
•
GSM1800/GSM1900: 0.7 V while TX burst and 0 V otherwise.
3.5.1.1 R7514 in place and working correctly?
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Check that the component is in place and solder joints are ok
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Disconnect the power supply from the phone and check R514 resistance value with an ohmmeter
3.5.1.2 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.
3.5.1.3 Retu ok?
3.5.2 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
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GSM transmitter has to be active before measurements. Procedure is explained in section
“Transmitter troubleshooting”.
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Set TX power level to the maximum (“5” in EGSM900 and “0” in GSM1800/GSM1900)
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Measurements can be done with an oscilloscope and a VOLTAGE probe.
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EGSM900:
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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
both currents.
