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: 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.

The RF section of the phone is build around two RF ASICS: Rx ASIC N7500 and Tx ASIC N7501. There are also two

PA’s on board, one for GSM (N7502) and another for WCDMA (N7503).

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

supply component (N7504) added to the PWB.

Please note that the grounding of the PA module is directly below the PA 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). N7501, N7500, both PAs and SMPS 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.

For additional RF troubleshooting instructions, see Appendix A. These instructions include descriptions/

instructions for RF self-tests as well as troubleshooting instructions for various fault cases.

RM-1 RF key component placement

The RF section of the phone is build around two RF ASICs, Rx ASIC N7500 and Tx ASIC N7501.

There are also two PAs on the board, one for GSM (N7502) and one for WCDMA (N7503). The WCDMA PA needs

variable supply voltage to work power efficiently and therefore there is a Switched Mode Power Supply (SMPS)

component (N7504) added to the PWB.

RM-1

RF Troubleshooting and Manual Tuning Guide Nokia Customer Care

Issue 1 Company Confidential Page 7–5