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If the output power is too low, measure the control voltage POWLEV at N450 pin 1 using an
oscilloscope.
It should look like in figure below Fig.8.2.
If the control voltage is too low, the fault usually is due to N800.
It can also be due to D600.
If the control voltage is correct, measure VREG at N450 pin 4 or N401 pin 3 +3.5 V
frequency.
If VREG is too low, the fault can be due to N450 or N401.
If VREG is correct, measure the signal TX at N570 pin 1 ~13 dBm.
If the signal TX is correct at N570 pin 1, check the output power from N401 pin 19 ~25 dBm.
If the output power is too low, replace N401.
If the output power is correct at N401, follow it from the output of the power amplifier to the
antenna through V412, Z203, V207 and Z205.
The fault usually is due to the antenna switch connection V207 and V208 with the surrounding
components.
If the signal TX is too low at N570 pin 1, measure the feed voltage at N570 pin 3 using an
oscilloscope ~3.8 V, 215 Hz.
If the feed voltage is correct, the fault usually is due to N570 or N401.
If the feed voltage is incorrect, the fault usually is due to V570 or V571.
For GSM 1800:
Start the transmitter in switch mode at channel 699 and DAC 7 value at "FF".
Check if there is enough output power 28- 32 dBm, at the antenna plate using the spectrum
analyser.
We propose the following settings while measuring:
CF- 1747.6MHz, SPAN- 0 Hz, RBW- 300 kHz, VBW- 100 kHz and Sweep- 0.8 ms.
If the output power is correct, the fault can be due to the frame.
The fault can also be due to a change, because of ageing, in the characteristic in some of the
components participating in the power regulation.
4/00021-3/FEA 209 544/18 B
Fig.8.2
Trouble Shooting Guide, Advanced
DC
, same
40(121)
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