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Trouble Shooting Guide, Advanced
If the amplitude and the frequency are correct, go to section 3.3.1.
If the frequency is correct, but the amplitude is too low, check the feed voltage at N302 pin 6
+3.7 V
.
DC
If the voltage is correct, replace N302.
If the voltage is incorrect, check VVCO +3.8 V
, SYNTON_DCS +3.7 V
and V301 with the
DC
DC
associated components.
If SYNTON_DCS is missing, check D103, D105 and D600.
If the amplitude is correct, but the frequency is incorrect, the fault usually depends on N301.
It can also depend on N303 or D600.
If the signal is several MHz wide, replace C318.
To measure the frequency more precisely you can lower SPAN to 1 MHz.
3.3.1 TX - synth fault
Perform a TxVCO calibration, a part of the radio calibration in EFRA.
If the phone passes the TxVCO calibration and the other radio calibrations, the fault has been
corrected.
A new calibration is needed to compensate the changes (due to ageing) of the characteristic in
some of the components in the TX-synth.
If the phone passes the TxVCO calibration but fails in at least one of the other radio
calibrations, go to the corresponding chapter.
If it does not pass the TxVCO calibration, it usually is due to too large moderation in the
feedback of the TX-synth, either in TXLOOP or in TXIF.
Give the board power and start the test program.
For GSM 900:
Start the transmitter in static mode on channel 62.
We propose the following settings on the spectrum analyser while measuring:
CF- 902.4 MHz, SPAN- 200 MHz, RBW- 10kHz, VBW- 10 kHz and Sweep- 30ms.
Measure the amplitude and the frequency on the signals TXLOOP_GSM at N201 pin 8, 9
-4 dBm, the frequency should be 902.4 MHz when the synth is locked on.
If the TXLOOP-signal is too low, the fault can be due to too large moderation in U202, C204 or
C205.
The fault can also be due to N570 ~12 dBm or its feed voltages.
If the level of the TXLOOP-signal is correct, check the amplitude on the signals LOINA and
LOINB at N201 pin 17, 18 ~ -10 dBm.
If the amplitudes on LOINA and LOINB are too low, the fault usually depends on U201 or the
components that belongs to it.
If the amplitudes on TXLOOP, LOINA and LOINB are correct, calculate the frequency on
TXIF_GSM by subtracting LOIN from TXIN.
On an approved phone it should be as follow:
TXIN 902.4 MHz - LOIN 772,4 MHz = TXIF_GSM 130 MHz.
4/00021-3/FEA 209 544/18 B
17(121)
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