General RF troubleshooting
General RF troubleshooting
Two types of measurements are used in the following. It will be specified if the measurement type is "RF" or
"LF".
• RF measurements are done with a Spectrum Analyzer and a high-frequency probe, for example Agilent
85024A. (Note that the test jig has some losses which must be taken into consideration when calibrating
the test system.)
• LF (Low frequency) and DC measurements should be done with a 10:1 probe and an oscilloscope. The probe
used in the following is 10MW/8pF passive probe. If using another probe then bear in mind that the
voltages displayed may be slightly different. Always make sure the measurement set-up is calibrated when
measuring RF parameters on the antenna pad. Remember to include the loss in the module repair jig when
realigning the phone.
Most RF semiconductors are static discharge sensitive, so ESD protection must be applied during repair
(ground straps and ESD soldering irons). FEM and Uppcosto are moisture sensitive so parts must be pre-baked
prior to soldering. Apart from key-components described in this document there are a lot of discrete
components (resistors, inductors and capacitors) for which troubleshooting is done by checking if soldering
of the component is done properly and checking if the component is missing from PWB. Capacitors can be
checked for short-circuiting and resistors for value by means of an Ohm meter, but be aware in-circuit
measurements should be evaluated carefully. In the following both the name EGSM and GSM850 will be used
for the lower band and both PCN and GSM1900 will be used for the upper band.
RF key components
Figure 30 RF key components on PWB
N7100
FEM(PA & Antenna Switch)
D7402
Uppcosto
Z7101
EGSM850/900 RX SAW filter
Z7100
DCS1800/PCS1900 RX SAW filter
Z7102
EGSM850/900 TX filter
D2901
Litti
B7402
26 MHz crystal
RM-305; RM-306
RF troubleshooting
Issue 2
COMPANY CONFIDENTIAL
Page 5 –5
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