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:
•
VAPAUS RFIC (N7500)
•
TX FEM (N7520)
•
WCDMA PA (N7540)
•
Mikki DC/DC converter (N7560)
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
visual inspection
.
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:
•
Module jig MJ-264
•
Flash adapter FS-145
•
Control unit CU-4/Interface adapter SS-46
•
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 a RF generator can be used. However, 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 (only if it is
possible to perform the measurement 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 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 verify functionality of the cellular RF block without removing RF shield.
Instructions for finding the faulty component are provided in some cases, but the whole RF block still needs
to be replaced even when a single component is faulty.
RM-627
RF troubleshooting
Issue 1
COMPANY CONFIDENTIAL
Page 4 – 5
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