NSW-5
Disassembly and Troubleshooting Instructions
PAMS Technical Documentation
Page 24
Issue 1 10/00
Nokia Mobile Phones Ltd.
RF Troubleshooting
Introduction
Measurements are done using a spectrum analyzer and a high–frequen-
cy probe (Local and reference frequencies and RF–powerlevels in inter-
mediate stages of TX/RX–chains). An oscilloscope is used to measure
DC–voltages and low frequency signals. A multimeter is also a useful
measurement instrument in fault finding.
The RF section is mainly built around EROTUS–IC (N750). The RF block
has separate external filters, UHF synthesizers, Power Amplifiers, TX
Driver amplifiers, LNA/Mixer and upconverter circuit for both frequency
bands. In TDMA1900 mode a RF regulator IC is provided to supply volt-
age for RF parts.
To simplify troubleshooting, this RF troubleshooting document is divided
into three bigger sections: Receiver, Transmitter and Synthesizer blocks.
The tolerances are specified for critical signals/voltages.
Before changing single ASICS or components, please check the following
details:
1. The soldering and connections of pins of ASICS
2. That supply voltages and control signals are OK
3. Signals from the synthesizers are coming to ASICS. This will
prevent unnecessary changing of ASICS.
Please note that the grounding of the Power Amplifier–IC is directly un-
derneath, so it is difficult to check. The PA is ESD sensitive! So ESD
precaution must be used when dealing with the PA–IC (ground straps and
ESD soldering irons). The PAs are also moisture sensitive components,
and it is important to follow additional information about handling the com-
ponents.
There are also lots of discrete components (resistors, inductors and ca-
pacitors) the troubleshooting of which is done just by checking that com-
ponent is soldered or that it is not missing from the PWB.
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