Nokia n80 User Manual

Also see for N 80: User guide User guide Software guide Supplementary guide User guide

Contents

Nokia n80 User Manual Manual pdf 221 page image

Introduction to RF troubleshootingAll measurements should be done using:• spectrum analyser with a low-impedance wideband passive probe (LO-/reference frequencies and RFpower levels).Note: When measuring frequencies of 4GHz, absolute level measurements are not possible withthis probe. Compare levels with a known good board.• 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 isno possibility to perform the measurements in a good performance RF-shielded room. Even lowpower WCDMA transmitters may disturb nearby WCDMA networks and cause problems to 3G cellularphone communication in wide area. WCDMA Tx measurements should be performed at least in anRF-shielded box and never with higher Tx power level than 0 dBm! Test full WCDMA Tx power onlyin RF-shielded environment.Also all measurements with an RF coupler should be performed in RF shielded environment becausenearby base stations can disturb sensitive receiver measurements. If there is no possibility to useRF shielded environment, it should be checked that there are no transmissions on the samefrequencies as used in the tests.The RF section of the phone is built around an RF ASIC, N7505, for the US variant and RF ASIC, N7500, for theEU variant. N7500 consists of the N7505 and several filters, so there are fewer discreet components in the EUvariant layout. Both versions have a GSM quad band dual PA and antenna switch module, TXFEM, N7520, anda WCDMA PA, N7540.The WCDMA PA needs a variable supply to work efficiently. This is provided by a switch mode power supplycomponent, N7541.Please note that the grounding of the PA module is directly below the PA module. Therefore, it is difficult tocheck or change the module.Most RF semiconductors are static discharge sensitive. ESD procedures must be followed during repair, groundstraps and ESD soldering irons. RF ASICs, TXFEM, PA 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.A 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 in the service manual are rough figures. Especially RFlevels vary because of different measuring equipment or different grounding of the probe used. All spectrumanalyser measurements in this manual are made with a Fluke PM9639/011 10:1 (500 ohm) probe. It isrecommended that a similar kind of probe is used for all troubleshooting measurements.When using an RF probe, use a pair of metallic tweezers to connect the probe ground to the PWB ground asclose to the measurement point as possible. If measurements are performed in a product specific modulejig, 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-91; RM-92RF Troubleshooting and Manual Tuning Guide Nokia Customer CareIssue 1 COMPANY CONFIDENTIAL Page 7 –5Copyright © 2006 Nokia. All rights reserved.