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Trouble Shooting Guide, Advanced
If the amplitude and the frequency are correct, go to section 5.2.2.
If the frequency is correct, but the amplitude is too low, check the feed voltage at N302 pin 6
+3.6 V
.
DC
If the voltage is correct, replace N302.
If the voltage is incorrect, check VVCO +3.8 V
, SYNTON_DSC +3.8 V
and V301 with the
DC
DC
belonging components.
If the amplitude is correct, but the frequency is incorrect, the fault usually is due to N301. It can
also be due to N302 or D600.
If the signal is several MHz wide, replace C318.
To make a more accurate frequency when measuring, try to lower SPAN to 1 MHz.
5.2.1 TX–synth fault for GSM900
The fault usually is due to too large attenuation in the feed back of the TX-synth, either at TXIN
or at TXIF.
Give the board power and start the test program.
Start the transmitter in static mode at channel 62.
We propose the following settings on the spectrum analyser while measuring:
CF- 902.4 MHz, SPAN- 200 MHz, RBW- 10 kHz, VBW- 10 kHz and Sweep- 30 ms.
Measure the amplitude and the frequency of the signals TXINA and TXINB at N201 pin 8, 9 ~ -
19 dBm, the frequency should be 902.4 MHz when the synth has locked on.
If the TXIN-signal is too low, the fault usually is due to N570, ~7dBm at N570 pin1 or its feed
voltage.
The fault can also depend on too large attenuation in U202, C204 or C205.
If the level of the TXIN-signal is correct, check the amplitude of the signals LOINA and LOINB
at N201 pin 18, 17. 772.4 MHz, ~ -15 dBm.
If the amplitude of LOINA or LOINB is too low, the fault usually depends on U201, C202 or
C203.
If the amplitudes of TXINA/B and LOINA/B are correct, calculate the frequency of TXIF by
subtracting TXIN from LOIN.
On an approved phone should it be as follow:
TXIN 902.4 MHz - LOIN 772.4 MHz = TXIF 130 MHz.
Change CF at the spectrum analyser to the calculated, according to the formula above,
frequency for TXIF and SPAN to 10 MHz.
The frequency of the transmitter usually is 890 MHz when the synth locks off, that gives a
TXIF-frequency of 117 MHz.
Measure the amplitude of TXIFA, TXIFB at N201 pin 13, 14 ~ -7 dBm.
If the amplitude is too low, the fault usually depends on N201.
If the amplitude is correct, follow the signal from N201 pin 13, 14 to N500 pin 10, 11 through
R211, R212, R205, C506, C507, C508 and C509.
If TXIF has got the correct amplitude at N500, the fault can be due to N500, N570, N800, D600
or the components at the output N500 pin 12.
4/00021-3/FEA 209 544/18 B
25(121)
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