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206 Frequency Synthesizer Fault Finding TM9100 Service Manual

9.7 VCO and Related Circuitry (VHF Radios)

Introduction If there is no fault with the power supplies, the PLL inputs and output, and

the loop filter, check the VCO and related circuitry. The procedures in this

section apply only to VHF radios; the VHF frequency bands are defined in

Table 9.4. There are six aspects:

■ Task 28: check VCO

■ Task 29: repair PLL feedback

■ Task 30: repair VCO

■ Task 31: check transmit-receive switch

■ Task 32: repair switching network

■ Task 33: check buffer amplifier

The measurement points for diagnosing faults in the VCO and related

circuitry are summarized in Figure 9.11.

Table 9.4 Minimum and maximum frequencies for the different VHF frequency bands

Frequency band Frequency in MHz

Minimum Maximum

B1 84 ± 5 200 ± 5

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