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Trouble Shooting Guide, Advanced
For GSM 1800:
Change CF on the spectrum analyser to 175 MHz.
Measure the signal 175 MHz, the frequency after the first mix, in to the filter Z250 ~ - 26dBm.
The filter attenuates the signal 8 - 10 dBm in the pass band.
If the filter attenuates the signal too much, is it usually Z250 or L206 that is faulty.
If the input signal to the filter is too low, is one of the input signals to the mixer, 1842.6 MHz
RXIN or 1667.6 MHz LO or the mixers amplification too low.
The mixers input signal usually is:
1842.6 MHz: ~ - 53 dBm on N202 pin 5, 6. Follow the signal from the antenna connection - 50
dBm to the mixer.
1667.6 MHz: ~ - 11 dBm on N202 pin 13,14 and ~ - 2dBm on N302 pin 1. Follow the signal
from LO VCO to the mixer.
If the mixer amplification is too low, is it usually N202 that is faulty, but sometime is it Z202.
Measure the signal 6 MHz coming out from N500 pin 2 through Z500, which attenuates the
signal approximately ~10 dBm.
Then measure the output signal from N500 pin 44 through a filter built by discreet components
and with low moderation, back to N500 pin 40.
If the signal 6 MHz is too low going out from N500 pin 2, 44, 33, 34, measure the voltage on
C530, C531, C532, C533, C534 and C535, ~2.1 V for an input signal of -50 dBm, the voltage
changes according to the level of the input signal.
The fault can be due to a short circuit in one of the capacitors or the 6 MHz filters.
15.2.3 Phase error or logical fault
For measuring phase error, go to Radio \ Sensitivity.
The RF-signal from the GSM test instrument must be non-modulated and the frequency must be
in accordance with the chosen channel.
For GSM 900:
At an input signal of -102 dBm should the phase error be: PEAK 0-65, RMS 0-16 deg.
The highest allowed frequency error is + 2000 Hz.
For GSM 1800:
At an input signal of -100 dBm should the phase error be: PEAK 0-65, RMS 0-16 deg.
The highest allowed frequency error is + 2000 Hz.
When both the Peak phase error and the RMS phase error (sometimes even the frequency error)
are too large, it usually is due to a too large attenuation in the signal path.
When both the Peak phase error and the RMS phase error (sometimes even the frequency error)
are too large, but all the radio signals have correct amplitude and frequency.
It can be due to anyone of N800, D600 or N500.
When the Peak phase error is 1, the RMS phase error is 0 and the frequency error is +2000 Hz it
can be a frequency fault on B510 or a fault on N800.
4/00021-3/FEA 209 544/18 B
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