Are Tx-Iq Signals Ok; Is Tx Vco Signal Level In The T7503 Output High Enough; Vctcxo Frequency And Output Level Correct - Nokia RM-57 Service Manual

Nokia Customer Care

3.3.3 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.

3.3.4 Is TX VCO signal level in the T7503 output high enough?

• GSM transmitter has to be active before TX VCO's output level can be measured. Procedure is
explained in section "Transmitter troubleshooting".
• Measurements can be done with a spectrum analyser and an RF probe. RBW and VBW =
1 MHz, Span = 0, sweep time 1 ms. Spectrum analyser centre frequency should be set
according the used TX channel (see section "Frequency mappings"). 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.
• Check the level of the VCO frequency in T7503 outputs. The level should be about
-30...-35 dBm in both output lines during GSM TX burst. 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.
3.3.4.1 TX VCO G7502 output level high enough?
GSM transmitter has to be active before TX VCO's output frequency and output level can be
•
measured. Procedure is explained in section "Transmitter 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 section "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.
• 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 span setting. The output level of the VCO should be about -25 dBm during GSM TX burst.
3.3.4.1.1 Replace TX VCO G7502
3.3.4.2 Replace balun T7503

3.3.5 VCTCXO frequency and output level correct?

• Measurement can be done with an oscilloscope and a probe.
Company Confidential
Copyright © 2005 Nokia. All rights reserved
Appendix A: RF Troubleshooting
A-63