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Trouble Shooting Guide, Advanced
If the feed voltage is incorrect, it is usually because of L560, C560 (short circuit), V570, V571
or one of the following voltage are missing: SWDC, same voltage as VBATT, VVCO +3.8 V
DC
or TXON_GSM +3.7 V
.
DC
For GSM 1800:
Measure the control voltage POWLEV on N450 pin 11 using an oscilloscope Fig. 15.2.
If the control voltage is too low, check the soldering at N800 pin 61.
If the soldering is fine, the fault usually depends on N800. It can also depend on D600 or a short
circuit in C833 or C853.
If the control voltage is correct, measure VREG on N450 pin 4 or N401 pin 3 +3.7 V
, same
DC
frequency.
If VREG is too low, replace N450. If that didn't work, it probably is N401 that is faulty.
If VREG is correct, measure the signal TXIN on N560 pin 1 ~12 dBm.
If the signal TXIN exists on N560 pin 1, make sure R408 and C441 are mounted.
If they are, check the output signal from N401 pin 18,19,24 or 25, ~27 dBm.
If the signal is missing, it probably is N401 faulty.
If it exist, check if it can be found on the anode of V205 (the side without a line).
If the signal is too low, replace V411.
If the signal is correct the fault is probably in the antenna switch connection (V201 and V206
with the associated components).
If the signal TXIN is missing, measure the feed voltage on N560 pin 6 using an oscilloscope
(~3.8 V, 215 Hz).
If the feed voltage is correct, replace N560.
If that didn't work, it probably is N401 that is faulty.
If the feed voltage is incorrect, it is usually because of L560, C560 (short circuit), V560, V561
or one of the following voltage are missing: SWDC same voltage as VBATT, VVCO +3.8 V
DC
or TXON_DCS +3.7 V
.
DC
All the mentioned signal strength levels are approximately, especially when measuring at
the signal before the power amplifier, since its output power radiates back to the probe.
This has to be considered when comparing measured values with reference values.
15.3.2 The switched output power is correct, but cannot connect a
call
Turn off switch TX.
Set the spectrum analyser to: SPAN- 1 MHz, RBW- 10 kHz, VBW- 10 kHz, SWEEP- 30 ms.
Start the transmitter in static mode with modulation on the channel 62 for GSM 900 and channel
699 for GSM 1800.
Make sure the spectra look like the one in fig below. Fig. 15.3.
4/00021-3/FEA 209 544/18 B
69(121)
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