User Guide

Introduction to RF troubleshooting

All measurements should 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)

Caution: Also all measurements with an RF coupler should be performed in RF shielded environment

because nearby base stations can disturb sensitive receiver measurements. If there is no possibility

to use RF shielded environment, it should be checked that there are no transmissions on the same

frequencies as used in the tests.

The RF section of the phone is build around one RF ASIC: ASIC N7505.

Note: Before changing N7505, please check the following things: supply voltages and serial

communication coming from baseband toN7505 are OK. Please note that the grounding of the Frond

End Module (FEM) is directly below FEM so it is difficult to check or change.

Most RF semiconductors are static discharge sensitive! ESD protection must be taken care of during repair

(ground straps and ESD soldering irons). N7505 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 as other components connected to the same node can change

the seen resistance.

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.

RF key component placement

The RF section of the phone is build around one RF ASIC: ASIC N7505.

RM-198

RF Troubleshooting and Manual Tuning Guide Nokia Customer Care

Issue 1 COMPANY CONFIDENTIAL Page 7 –5