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Spectrum analyser RBW and VBW = 1 MHz, Span = 0, sweep time 1 ms. Notice that GSM
transmission has pulsed nature and VCO output power should be measured during TX burst
(triggering needed). Another possibility is to use following settings: RBW = VBW = 1 MHz, Span
200 kHz and sweep time at least 2.5 seconds.
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Connect the RF probe to the T7503 input. VCO shield has to be removed before measurement.
Remember to solder the shield back after the phone repairing.
Check if the frequency of the TX VCO is as expected. If the VCO signal is not found try to use wider
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span setting. The output level of the VCO should be about -25 dBm during GSM TX burst.
3.4.4.1.1 Replace TX VCO G7502
3.4.4.2 Replace balun T7503
3.4.5 Replace Vinku (N7501) or GSM PA (N7502) or both
3.5 TX power vs. time ok?
This section means situation when GSM TX power levels are ok, but burst timing is not correct or power changes
during TX burst.
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GSM transmitter has to be active before measurements. Procedure is explained in section
"Transmitter troubleshooting". Note! It is probably needed to change the Tx Data Type in Phoenix to
"Random" before this measurement can be performed.
Measurement can be done with a GSM transmitter tester or other GSM communication tester.
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Attach the phone to the product specific test jig and the measurement device to the RF-coupler.
Coupler attenuation should be also taken into account during measurements.
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If TX power vs. time 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).
3.5.1 Is the TXC-signal coming to Vinku ASIC (N7501) OK?
GSM transmitter has to be active before TX control voltage TXC can be measured. Procedure is
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explained in section "Transmitter troubleshooting".
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Set TX power level first to the maximum ("5" in EGSM900 and "0" in GSM1800/GSM1900)
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Measurement can be done with an oscilloscope and a probe.
Connect the probe to C7549
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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.
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GSM1800/GSM1900: 1.8 V while TX burst and 0 V otherwise.
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A-68
(EGSM900 TX power level 5) and voltage levels should be roughly:
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Appendix A: RF Troubleshooting
6.5.2 "TXC in GSM
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