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Appendix A: RF Troubleshooting
If TX signal is not found at all use wider span setting and check if the transmitter is transmitting
•
on wrong frequency. If signal is found to be on wrong frequency or frequency is not stabile, see
section,
3.1.1.1 Is Vinku (N7501) transmitting RF-power at all?
•
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.
•
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
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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.
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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
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Minimum power level – Output level should be about -55...-65 dBm
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Check if output levels of Vinku are as expected.
•
•
NOTE!
means that Vinku ASIC (N7501) is faulty or the ASIC is badly soldered. For example: VINKU is not
transmitting at all in EGSM900-band but TX-power is ok in other GSM-bands. Then it's quite clear
that VINKU (N7501) is faulty or badly soldered and the component should be replaced.
3.1.1.1.1 RF operating voltage VBAT_ASIC?
•
Measurement can be done with an oscilloscope and a probe.
•
Connect the probe to C7503 (or C7501, C7541)
•
VBAT_ASIC voltage level should be 3.05 – 5.4 V. Typical value is 4.0 V.
3.1.1.1.1.1 Ferrite inductor L7503 ok?
•
Check that component is in place and solder joints are ok
•
Measure voltage from the both ends of L7503. Is it faulty or is there short circuit in RF end?
3.1.3. "GSM transmitter frequency correct".
If VINKU output RF-power is totally missing just in one or two GSM-bands, typically this
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