User Guide

General RF troubleshooting

Introduction to RF troubleshooting

Soldered metal shieldings and components below them are not allowed to be changed or removed. The

purpose of the following troubleshooting document is only to identify possible RF faults and advice how to

tune the phone if it is necessary.

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: A mobile phone WCDMA transmitter should never be tested with full Tx power, if there is

no possibility to perform the measurements in a good performance RF-shielded room. Even low

power WCDMA transmitters may disturb nearby WCDMA networks and cause problems to 3G cellular

phone communication in wide area. WCDMA Tx measurements should be performed at least in an

RF-shielded box and never with higher Tx power level than 0 dBm! Test full WCDMA Tx power only

in RF-shielded environment.

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 built around one RF ASIC N7505. There are also GSM TXFEM (integrated PA and

front end module) N7520 and WCDMA PA N7540 on board.

The WCDMA PA needs variable supply voltage to work properly, and therefore there is a switched mode power

supply component added to the PWB (N7541).

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

(ground straps and ESD soldering irons). The RF ASICs, both PAs and SMPS are moisture sensitive, so parts

must be pre-baked prior to soldering.

RM-244

RF troubleshooting

Issue 1 COMPANY CONFIDENTIAL Page 4 –5