Introduction To Rf Troubleshooting; Rf Key Components - Nokia RM-51 Service Manual

RM-51
RF troubleshooting

Introduction to RF troubleshooting

This document describes RF troubleshooting and tuning. In general, two types of measurements have to be
done during troubleshooting and repair of phones:
• RF measurements shall be done with a spectrum analyzer, either connected directly to the RF connector of
the RF adapter board SA-38, or used together with a high-frequency probe to measure RF signals at points
along the TX or RX chain.
• LF (Low-Frequency) and DC measurements shall be done either with a multimeter, or with an oscilloscope
together with a 10:1 probe.
All tuning must be done with Phoenix Service Software a15_2004_7_55.exe_, or later.
Always make sure that the measurement set-up has been calibrated when measuring RF parameters at the RF
connector. Remember to include the correct losses in the module repair jig and the connecting cable when
realigning the phone.
Most RF semiconductors are electrostatic discharge (ESD) sensitive. ESD protection must be taken into account
during repair (ground straps and ESD soldering irons).
RF calibration done via Phoenix software is temperature sensitive because of calibration of 26MHz reference
oscillator (VCXO). According to the Helgo specification, the ambient temperature has to be in the range of 22 to
38C.
Note: In this text the following terms are used interchangeably:
• GSM900 = EGSM900 = EGSM
• GSM1800 = DCS band = PCN band
• GSM1900 = PCS band
The first step of fault-finding should always be a visual inspection. Carefully inspect the RF area using a
microscope and look for solder bridges, missing components, short circuits, components that have partially
come off and other anomalies. Capacitors can be checked to see that they are not short-circuited, and inductors
that they are not open circuits. Also check that power supply lines are not short-circuited, i.e. not 0Ω to ground.
Instruments needed for troubleshooting (minimum requirement):
• oscilloscope
• multimeter
• spectrum analyzer (SA)
Note: Always use an attenuator at the spectrum analyzer input to ensure that the SA will not become
damaged by excessive input power from the phone. Check the spectrum analyzer for maximum
allowable input power.
For example, when transmitting in the EGSM band at max power level, the output power will be around
+33dBm. By using a 10dB attenuator the actual input to the SA will then be +23dBm. Also adjust the
internal attenuator so that the transmitted signal is reduced to less than around -10dBm in order to
avoid saturation of SA input stage.
• power supply that can deliver at least 2Adc
• Nokia MJ-30 module jig (also called test jig)
• RF adapter SA-38
• PC with Phoenix installed
• PKD-1 deskey dongle for Phoenix

RF key components

The following figure shows the key components of the RF section:
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