General Rf Troubleshooting; Introduction To Rf Troubleshooting - Nokia RM-235 Service Manual

RM-235
RF troubleshooting

General RF troubleshooting

Introduction to RF troubleshooting

Most RF semiconductors are static discharge sensitive
ESD protection must be applied during repair (ground straps and ESD soldering irons).
Pre-baking
These parts are moisture sensitive and must be pre-baked prior to soldering:
• RFIC N7505
• Front End Module (FEM) N7520
Discrete components
In addition to the key-components, there are a number of discrete components (resistors, inductors and
capacitors) for which troubleshooting is done mainly by
Capacitors: check for short circuits.
Resistors: check value with an ohm meter.
Note: In-circuit measurements should be evaluated carefully
Measuring equipment
All measurements should be done using:
• An oscilloscope for low frequency and DC measurements. Recommended probe: 10:1, 10Mohm//8pF.
• A radio communication tester including RF generator and spectrum analyser, for example Rohde & Schwarz
CMU200. (Alternatively a spectrum analyser and an RF generator can be used. Some tests in this guide are
not possible to perform if this solution is chosen).
Note: A mobile phone WCDMA transmitter should never be tested with full TX power (it is only
possible to perform the measurements in a good RF-shielded room). Even low power WCDMA
transmitters may disturb nearby WCDMA networks and cause problems to 3G cellular phone
communication in a wide area.
Note: All communication Test Set Screen dumps are from CMU200. Other testers are different.
Note: All measurements with an RF coupler should be performed in an RF-shielded environment
because nearby base stations can disturb sensitive receiver measurements. If there is no possibility
to use RF shielded environment, testing at frequencies of nearby base stations should be avoided.
Level of repair
The scope of this guideline is to enable repairs at key-component level. Some key-components are not
accessible without replacing the whole shield frame (i.e. not replaceable). Please refer to the list of
replaceable RF components (page
Issue 1
4–7).
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