6881096C74-B May 25, 2005
Troubleshooting Procedures: VHF (136–174 MHz) Band Main Board Troubleshooting 4-7
4.6.3 Out-of-Lock Condition
The probable cause of an out-of-lock condition is a failure in the synthesizer circuit. If the voltages on
the AUX 1*, AUX 2*, AUX3*, and AUX4* lines do not conform to required output frequency in
Table 4-5, troubleshoot the synthesizer.
If the AUX 1* to AUX 4* voltages are correct but the synthesizer feedback level is not within the
range indicated, troubleshoot the feedback path.
If the AUX 1* to AUX 4* voltages are correct and the synthesizer feedback level is correct but an
out-of-lock condition persists, troubleshoot the synthesizer.
4.6.4 FGU Troubleshooting Aids
The following illustrations are additional service aids for troubleshooting the frequency generation
unit.
• Figure 4-1 on page 4-8 is a block diagram of the DC distribution for the frequency generation
unit.
• Figure 4-2 on page 4-9 is a block diagram of the frequency generation unit.
• Table 4-6 on page 4-9 describes the function of pins on the LV Frac-N IC U3751.
• Figure 4-3 on page 4-11 is a waveform representation during programming of the LV Frac-N IC
U3751.
Table 4-5. AUX Output Frequency Requirements
Frequency
Range
AUX 1 AUX 2 AUX 3 AUX 4 Output Frequency
HI LOW LOW LOW 136–155 MHz
LOW HI LOW LOW 155–174 MHz
LOW LOW HI LOW 245.65–264.65 MHz
LOW LOW LOW HIGH 264.65–283.65 MHz
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