User Guide

Nokia Customer Care

RM-1

RF Troubleshooting

Company Confidential

7A - 44

Issue 1

3.1.3.1.2 TX VCO control voltage VC ok?

• GSM transmitter has to be active before TX VCO control voltage VC can be measured.

Procedure is explained in chapter “General instructions for TX troubleshooting”.

• Measurement can be done with an oscilloscope and a probe.

• Connect the probe to R7519.

• Typical TX VCO control voltage VC should look somehow similar to figure 6.5.3. DC voltage

level should change if TX channel is changed. VC is lower on lower channels and higher if

higher channel numbers are used.

3.1.3.1.2.1 VCP2-voltage ok?

• GSM transmitter has to be active before VCP2 voltage can be measured. Procedure is

explained in chapter “General instructions for TX troubleshooting”.

• Measurement can be done with an oscilloscope and a probe.

• Connect the probe to C2221 (or C7550).

• VCP2 voltage should be about 4.75 V.

3.1.3.1.2.2 Vinku (N7501) RB_EXT voltage ok?

• GSM transmitter has to be active before Vinku’s RB_EXT voltage can be measured.

Procedure is explained in chapter “General instructions for TX troubleshooting”.

• Measurement can be done with an oscilloscope and a probe.

• Connect the probe to R7521.

• RB_EXT voltage should be 1.325 – 1.375 V.

3.1.3.1.2.3 Balun T7503 ok?

• GSM transmitter has to be active before TX VCO’s output level can be measured. Procedure

is explained in chapter “General instructions for TX troubleshooting”.

• Measurements can be done with a spectrum analyser and an RF probe. Spectrum analyser

centre frequency should be set according the used TX channel (see chapter “Frequency

mappings”).

• 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.