Rx Vhf Lo Troubleshooting - Nokia 6255 Rf Description And Troubleshooting

Nokia Customer Care

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.
3
2
RF Rx ASIC
1
Table 17 shows the description for each component in Figure 49.
Test
Point
1
2
3
4
5
Issue 2 05/2005
4
5
CDMA IF SAW filter
Figure 49: Rx VHF LO test points
Table 17: Rx VHF Layout Components
Description
VIO
Rx LO 256.2MHz
Rx LO lock voltage
VR7
VR5
©2005 Nokia Corporation
6255/6255i/6256/6256i (RM-19)
RF Description and Troubleshooting
AMPS IF
XTAL filter
LNA/Mixer/
Downconverter
Value
1.8V
-60 to -65dBm
1.2 to 1.7Vdc
2.8V
2.8V
Company Confidential Page 59