User Guide

6235/6235i/6236i (RM-60)

RF Description and Troubleshooting

UHF Synthesizer Schematic

UHF Synthesizer Troubleshooting

The UHF LO frequency varies with the channel and can be calculated using the Frequency

Calculator dialog box in the Phoenix RF component (see Figure 50 on page 53). 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"onpage54).

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 = 2.76VDC

4. If the frequency of the LO is not correct, check the DC voltages at the following:

• R7210, VR1A, supply line for PLL charge pump = 4.76VDC

5. 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 2

UHF PLL IC

Loop filter

components

Dual-band VCO

Lock voltage