6235/6235i/6236i (RM-60)RF Description and TroubleshootingPage 52 ©2005 Nokia Corporation Company Confidential Issue 1 04/2005UHF Synthesizer SchematicUHF Synthesizer TroubleshootingThe UHF LO frequency varies with the channel and can be calculated using the FrequencyCalculator dialog box in the Phoenix RF component (see Figure 50 on page 53). Use thefollowing steps to troubleshoot the UHF LO frequency.1. Ensure that the LO is locked. Set a channel and check the output of the UHF LOat L7200 within a very narrow span of 100KHz. The LO must be virtuallyimmobile.2. Measure the nominal UHF LO signal levels (see "UHF Synthesizer TestPoints" on page 54).3. If you do not see the presence of any LOs, check the DC voltages at the following:• R7203, VR4, supply line for VCO IC and PLL IC = 2.76VDC4. If the frequency of the LO is not correct, check the DC voltages at the following:• R7210, VR1A, supply line for PLL charge pump = 4.76VDC5. Ensure that the lock voltage at C7215 is between 1V and 3V.6. Check the RF return at R7204.• TX UHF LO (Cell/AMPS) = Tx frequency x 4• TX UHF LO (PCS) = Tx frequency x 2UHF PLL ICLoop filtercomponentsDual-band VCOLock voltage
