Nokia RM-57 Service Manual page 251

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3.1.1.4.1 Replace Hinku (N7500)
3.1.1.5 Replace antenna Switch Z7503
3.1.2 Does GSM TX transmit enough RF-power and power levels otherwise ok?
3.1.2.1 Is Vinku ASIC (N7501) transmitting correct RF-power?
• GSM transmitter has to be active before Vinku'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 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.
• GSM850/EGSM900:
Connect the RF probe to Z7504 input. The level should be about the same on both input pins.
-
Check output level with at least the maximum (5) and the minimum (19) power levels.
Maximum power level – Output level should be about -15...-25 dBm
-
Minimum power level – Output level should be about -45...-55 dBm
-
• GSM1800/GSM1900:
Connect the RF probe to C7577 or C7575. The level should be about the same on both
-
capacitors. Check output level with at least the maximum (0) and the minimum (15) power
levels.
Maximum power level – Output level should be about -25...-35 dBm
-
Minimum power level – Output level should be about -55...-65 dBm
-
• Check if output levels of Vinku are as expected.
NOTE!
•
typically this means that Vinku ASIC (N7501) is faulty or the ASIC is badly soldered. Of course
If VINKU ASIC is transmitting wrong TX power just in one or two GSM-bands,
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Appendix A: RF Troubleshooting
A-33