6881076C25-E September 5, 2008
Troubleshooting Procedures: VCO Procedures 4-13
4.3 VCO Procedures
This section provides band-specific troubleshooting procedures for the VCO.
4.3.1 VHF Band
Use these instructions along with the Theory of Operation, the block diagram, and the schematic to
help isolate failures: first, to the individual circuits, and finally, to the failing piece part.
4.3.1.1 VCO Hybrid Assembly
The VCO hybrid substrate is glued to the carrier board. The hybrid is not a field-repairable assembly.
If a failure is indicated in this assembly, replace the complete hybrid. You will need a hot-air source
to heat and soften the glue to separate the hybrid from the carrier board. If no hot-air source is
available, replace the entire carrier board.
4.3.1.2 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* and AUX 2* lines do not conform to
Table 4-7 on page 4-15, troubleshoot the synthesizer.
If the AUX 1* and AUX 2* voltages are correct but the synthesizer feedback level is not within the
range indicated, troubleshoot the first buffer on the VCO carrier board. If no problem is found with the
first buffer and the level out of the VCO is below that indicated on the block diagram, then replace the
VCO assembly.
If the AUX 1* and AUX 2* voltages are correct and the synthesizer feedback level is correct but an
out-of-lock condition persists, troubleshoot the synthesizer.
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