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•
Check the level of the TX VCO frequency in T7503 outputs. The level should be about -30...-35 dBm
in both output lines. If the signal level is correct in the input (about -25 dBm) but output level is
not as expected then replace T7503. VCO shield has to be removed before measurement.
Remember to solder the shield back after the phone repairing.
3.1.1.1.7.1 Replace balun T7503
3.1.1.1.8 Are TX-IQ signals ok?
•
These current mode signals are not possible to measure, but are tested with self-tests. So if there
is no fail in 2.3. "ST_CDSP_TX_IQ_TEST" these signals should be ok. Otherwise Vinku (N7501) or
RAP3G (D2800) is faulty. Notice that it is not possible to replace RAP3G ASIC.
3.1.1.1.9 Is there TXC-signal coming to Vinku ASIC (N7501)?
•
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 EGSM900 and "0" in GSM1800/GSM1900)
•
Measurement can be done with an oscilloscope and a probe.
•
Connect the probe to C7549
•
Typical TX control voltage TXC timing should look somehow similar to figure
mode (DC Offset 0 V)"
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:
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.
A-30
(EGSM900 TX power level 5) and voltage levels should be roughly:
Company Confidential
Copyright © 2005 Nokia. All rights reserved
Appendix A: RF Troubleshooting
6.5.2 "TXC in GSM
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