Introduction To Rf Troubleshooting; Rf Key Component Placement - Nokia RM-57 Service Manual

RM-57/58
RF Troubleshooting and Manual Tuning 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)
The RF section of the phone is build around two RF ASICS: Rx ASIC N7500 and Tx ASIC N7501. There is also one
PA on board (N7502).
Note: The grounding of the PA module is directly below the PA module. Therefore, it is difficult to
check or change the module.
Note: Most RF semiconductors are static discharge sensitive! ESD protection must be taken care of
during repair (ground straps and ESD soldering irons). N7501, N7500, 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.
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.

RF key component placement

The RF section of the phone is build around two RF ASICs, Rx ASIC N7500 and Tx ASIC N7501.
There is one PA on the board, N7502.
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