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Trouble Shooting Guide, Advanced
If the transmitter does not have any output power or if it does not lock on, go to chapter "Static
TX-fault.
If the transmitter locks on, start the transmitter in switch mode on channel 699, with DAC 7
value on "FF". Check if there is output power, 28 - 32 dBm, at the antenna plate using the
spectrum analyser.
We propose the following settings on the spectrum analyser:
CF- 1747.4 MHz, SPAN- 0 Hz, RBW- 300 kHz, VBW- 100 kHz and Sweep- 0.8 ms.
If there is no output power at all or if it is too low, go to section15.3.1.
If the output power is correct, go to section 15.3.2.
15.3.1 Low or no switched output power
For GSM 900:
Measure the control voltage POWLEV on N450 pin 11 Fig. 15.2. 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 +3.5 V
, same
DC
frequency.
If VREG is too low, replace N450.
If that didn't work, is it probably N401 that is faulty.
If VREG is correct, measure the signal TXIN on N570 pin 1 ~13 dBm.
If the signal TXIN exists on N570 pin 1, make sure R405 and C440 are mounted.
If they are, check the output signal from N401 pin 18,19,24 or 25, ~25 dBm.
If the signal is missing, it probably is N401 faulty.
If it exist, check if it can be found on the anode of V207, at the side without a line.
If the signal is too low, replace Z203.
If the signal is correct the fault is in the antenna switch connection, usually is L223 or L225
faulty.
If the signal TXIN is missing, measure the feed voltage on N570 pin 6 using an oscilloscope,
~3.8 V, 215 Hz.
If the feed voltage is correct, replace N570.
If that didn't work, it probably is N401 that is faulty.
4/00021-3/FEA 209 544/18 B
68(121)
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