Transmitter Fault Finding; General; Antenna Switch; Pa-Module, Directional Coupler And Power Detector - Nokia NSB-7 Series Service Manual

NSB-7
Disassembly & Troubleshooting

Transmitter fault finding

General

Middle channel 661 is used as a test channel (1880 MHz). Signal levels and forms are
referred to in RF testpoints. Signal levels can vary depending the measurement method.
So it is recommended to make measurements by your way and make own reference level
table. The phone which you are using for this reference table must be undamaged.
Set the wanted operating channel and power level.

Antenna Switch

When TX mode is in use only burst mode can be used. Antenna switch is controlled with
a pulse in control line. This antenna switch control signal can be measured in points
TX16. Shape of these control signals can be seen in RF measurement points.
Antenna switch operation can be checked by measuring the signal level from points TX12
and TX21. Specified loss for antenna switch is 1.2 dB but measurement can give some dB
more attenuation depending of the method. Check the level from reference engine.

PA-Module, Directional Coupler and Power Detector

At first the input signal level of the PA should be checked. Input signals can be measured
from point TX15. Refer the levels to reference engine and RF Testpoints.
Output of the PA can be checked by measuring the DET0 signal coming out from detec-
tor. Measure DET0 from TX11 and refer to the RF measurement points. If this is OK then
PA module, Directional coupler and Power Detector are working ok.
If DET0 is not ok check the supply of the detector TXVdet TX6 and check also the input of
the detector by measuring the point TX22 with spectrum analyzer. Refer the results to RF
Testpoints.
If the TX6 is ok but TX22 not then check PA power control line Vpd if Vpd is ok check the
components in RF signal path and check the PA supply voltage.

HAGAR

RF path

If RF output from HAGAR seems not be ok then IQ input signals from BB to Hagar should
be tested. These signals can be measured from points TX8 and TX9 and signals can be
referred to RF Testpoints.

Power control

Check the TXC point TX10 DET0 point TX11 and Vpd point TX19 refer the results to RF
measurement points. If only Vpd fails then Hagar power control has problems.
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PAMS Technical Documentation
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