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September 5, 2008 6881076C25-E

4-16 Troubleshooting Procedures: VCO Procedures

4.3.2.2 Out-of-Lock Condition

The probable cause of an out-of-lock condition is a failure in the synthesizer circuit. (See

Section 4.1.4.2 on page 4-7.) If the voltages on the AUX 1*, AUX 2*, or -8V lines at P0601 do not

conform to the values shown in Figure 4-2 on page 4-17, check the pin shift circuitry on the carrier

board for proper operation. If no trouble is found, troubleshoot the synthesizer.

If the AUX1*, AUX2*, and -8-V voltages are correct at P0601, check the pin shift circuitry on the

carrier board for proper operation. If no problem is found, probe the level of the synthesizer feed

back at P0601-1 using an RF millivoltmeter. The meter should indicate greater than -15 dBm. If it

does not, troubleshoot the synthesizer feedback circuitry; then troubleshoot the first buffer on the

VCO carrier board. If no trouble is found and the level out of the VCO is below that indicated on the

block diagram, then replace the VCO assembly.

If the AUX 1*, AUX2*, and -8-V voltages are correct and the synthesizer feedback level is correct but

an out-of-lock condition persists, troubleshoot the synthesizer.

4.3.2.3 No or Low Output Power (TX or RX Injection)

Using an RF millivoltmeter, probe the synthesizer feedback level at P0601-1. If the meter indication

is not greater than -15 dBm, troubleshoot the first buffer. If no failure is found and the level out of the

VCO (measured into 50 ohms at the RF output of the hybrid) is below that indicated in the block

diagram, then replace the VCO assembly.

If the level of synthesizer feedback at P0601-1 is correct, troubleshoot the doubler, second buffer,

and then the RX/TX pin diode switch.

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