Nokia RM-42 Service Manual

Also see for RM-42: Service manual

Contents

Introduction to RF troubleshootingAll measurements should be done using:• spectrum analyser with a high-frequency high-impedance passive probe (LO-/reference frequencies and RFpower 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 nopossibility to perform the measurements in a good performance RF-shielded room. Even low powerWCDMA transmitters may disturb nearby WCDMA networks and cause problems to 3G cellular phonecommunication in wide area. WCDMA Tx measurements should be performed at least in an RF-shieldedbox and never with higher Tx power level than 0 dBm! Test full WCDMA Tx power only in RF-shieldedenvironment.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 use RFshielded environment, it should be checked that there are no transmissions on the same frequenciesas used in the tests.The RF section of the phone is build around two RF ASICS: Rx ASIC N7500 and Tx ASIC N7501. There are also twoPA’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 powersupply 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 tocheck 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 mustbe pre-baked prior to soldering.In addition to key components, there are lot of discrete components (resistors, inductors and capacitors) whichtroubleshooting 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-circuitmeasurements should be evaluated carefully.Keep in mind that all measured voltages or RF levels depicted in the service manual are rough figures. EspeciallyRF levels 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 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.RF key component placementThe 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 needsvariable supply voltage to work power efficiently and therefore there is a Switched Mode Power Supply (SMPS)component (N7504) added to the PWB.RM-42RF Troubleshooting and Manual Tuning Guide Nokia Customer Care9241872 (Issue 1) Company Confidential Page 7–5Copyright ©2005 Nokia. All Rights Reserved.