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

9.5

Receive VCO and Related Circuitry (UHF Radios)

Introduction
Table 9.3 Minimum and maximum receive frequencies for the different UHF frequency bands
Frequency band
H5
H6/H7
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 UHF radios with a lock error or receive fault, and
therefore with suspect receive VCO and related circuitry. (The minimum
and maximum receive frequencies for the different UHF frequency bands
are defined in Table 9.3.) There are six aspects:
Task 17: check receive VCO
Task 18: repair PLL feedback
Task 19: repair receive VCO
Task 20: check switching to receive mode
Task 21: repair switching network
Task 22: check receive buffer amplifier.
The measurement points for diagnosing faults in the VCO and related
circuitry are summarized in
Receive frequency in MHz
Minimum
337 ± 5
378 ± 5
Figure 9.9.
Maximum
441 ± 5
498 ± 5
Frequency Synthesizer Fault Finding 203