Vco And Related Circuitry (Vhf Radios) - Tait TM8235 Service Manual

9.7

VCO and Related Circuitry (VHF Radios)

Introduction
Table 9.5 Minimum and maximum frequencies for the different VHF frequency bands
Frequency band
A4
B1
C0
D1
TM8100/TM8200 Service Manual
© Tait Electronics Limited June 2006
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 9.5. 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
Frequency in MHz
Minimum
55 ± 5
84 ± 5
137 ± 5
167 ± 5
Figure 9.12.
Maximum
125 ± 5
200 ± 5
247 ± 5
287 ± 5
Frequency Synthesizer Fault Finding 217