Nokia 6680 RM-36 Service Manual page 322

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and VBW = 1 MHz, Span ≤ 200 kHz.
• 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.
4.1.1.1.7.1 Replace balun T7503
4.1.1.1.8 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.
4.1.1.1.9 Is the TXC-signal coming to Vinku ASIC (N7501) OK?
WCDMA transmitter has to be active before TX control voltage TXC can be measured. Procedure is
•
explained in section "Transmitter troubleshooting".
• Set TX power level to -50 dBm (Set start level "-50" to Phoenix)
• Measurement can be done with an oscilloscope and a probe.
• Connect the probe to C7549
• TX control voltage TXC should be constant DC-voltage between 0.1 - 2.3 V. Voltage level should
change if TX power is changed. TXC is lower on lower power levels and higher if higher power
levels are used.
• TXC voltage should be about 1.0 V with power level -50 dBm and about 1.5 V with power level
0 dBm.
4.1.1.1.9.1 R7514 in place and working correctly?
• 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
4.1.1.1.9.2 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 C7549 is not
short-circuited.
4.1.1.1.9.3 Retu ok?
4.1.1.1.10 WCDMA-modulator supply voltage (VREG2) ok?
• WCDMA transmitter has to be active before measurements. Procedure is explained in section
"Transmitter troubleshooting".
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Appendix A: RF Troubleshooting