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RM-272; RM-273
RF Troubleshooting and Manual Tuning Guide
Introduction to RF troubleshooting
On the following pages you will find a step-by-step troubleshooting procedure and reference measurements
at the relevant signal points. For functional descriptions, please refer to the System module section.
Notes on reference measurements
All measurements must be done using:
• spectrum analyser with a high-frequency high-impedance passive probe (LO-/reference frequencies and
RF power levels)
• oscilloscope with a 10:1 probe (DC-voltages and low frequency signals)
Important:
or where there are no transmissions on the same frequencies. This may disturb sensitive receiver
measurements.
Repairing this phone - important
The RF section of the phone is built around one RF ASIC. Before changing the RF ASIC, please make sure that
supply voltages and serial communication coming from baseband to RF are OK.
Please note that the grounding of the FEM module is directly below the FEM module. Therefore, it is difficult
to check or change the module.
Most RF semiconductors are static discharge sensitive! ESD protection must be taken care of during repair
(ground straps and ESD soldering irons). The RF ASIC and FEM are moisture sensitive, so parts must be pre-
baked prior to soldering.
In addition to key components, there are lot of discrete components (resistors, inductors and capacitors)
which troubleshooting is done mainly by checking if the soldering of the component is done properly.
Capacitor can be checked for shorts and resistors for value by means of an ohmmeter, but be aware in-circuit
measurements should be evaluated carefully.
Keep in mind that all measured voltages or RF levels depicted in the service manual are rough figures.
Especially RF levels vary because of different measuring equipment or different grounding of the probe used.
When using an RF probe, use a pair of metallic tweezers to connect the probe ground to the PWB ground as
close to the measurement point as possible. If measurements are performed in a product specific module
jig, then "GND" pads should be used for the probe ground.
Supported bands
The following part of the service manual contains a description of all four GSM bands. It covers both variants,
RM-272 and RM-273. Both variants support three GSM bands as follows:
• RM-272: GSM900, GSM1800, GSM1900
• RM-273: GSM850, GSM1800, GSM1900
Make sure to investigate only the bands, which the phone is made for.
Issue 1
All measurements with an RF coupler must be performed in an RF shielded environment,
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