User Guide

Nokia Customer Care RF Description and Troubleshooting

6255/6255i/6256/6256i (RM-19)

Rx VHF LO Troubleshooting

The VHF LO operates at a fixed frequency of 256.2MHz. It is the second LO for down-

conversion to I and Q for baseband processing. Use the following steps to troubleshoot

the VHF LO.

1. Monitor the test point at C710. Ensure that a locked and stable 256.2MHz with

amplitude ~ –60dBm is present on the spectrum analyzer (or, with a high

impedance probe, ~ -2dBm at C7104).

2. Monitor the control voltage at C7100. The control voltage at a locked state must

be between 1.2 and 1.7 Vdc for the proper operation of the VHF LO.

Figure 49: Rx VHF LO test points

Table 17 shows the description for each component in Figure 49.

Table 17: Rx VHF Layout Components

Test

Point

Description Value

1 VIO 1.8V

2 Rx LO 256.2MHz -60 to -65dBm

3 Rx LO lock voltage 1.2 to 1.7Vdc

4 VR7 2.8V

5 VR5 2.8V

RF Rx ASIC

CDMA IF SAW filter

AMPS IF

XTAL filter

LNA/Mixer/

Downconverter