User Guide

6255/6255i/6256/6256i (RM-19)
RF Description and Troubleshooting Nokia Customer Care
Page 56 ©2005 Nokia Corporation Company Confidential Issue 2 05/2005
Figure 46: Tx Output for AMPS channel 384, power level 5
UHF Synthesizer
The UHF LO frequency varies with the channel and can be calculated using the Frequency
Calculator dialog box in the Phoenix RF component. Use the following steps to
troubleshoot the UHF LO frequency.
1. Ensure that the LO is locked. Set a channel and check the output of the UHF LO
at L7200 within a very narrow span of 100KHz. The LO must be virtually
immobile.
2. Measure the nominal UHF LO signal levels (see "UHF Synthesizer Test
Points" on page 57).
3. If you do not see the presence of any LOs, check the DC voltages at the following:
• R7209, VR4, supply line for VCO IC and PLL IC = 2.76VDC
4. If the frequency of the LO is not correct, check the DC voltages at the following:
• R7208, VR1A, supply line for PLL charge pump = 4.76VDC
5. Ensure that the lock voltage at C7220 is between 1V and 3V.
6. Check the RF return at R7210.
• TX UHF LO (Cell/AMPS) = Tx frequency x 4
• TX UHF LO (PCS) = Tx frequency x 2