Tait TM8100 mobiles, Service Manual

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234 Frequency Synthesizer Fault Finding TM8100/TM8200 Service Manual
© Tait Electronics Limited November 2007
9.8 Power Supply for FCL
Fault-Diagnosis
Stages
Indications of a fault in the FCL will have been revealed by the initial checks
in
“Initial Checks” on page 186 and the PLL checks in “Phase-locked
Loop” on page 198 . In the latter case a fault with the reference frequency
input from the FCL to the PLL will imply that the FCL is suspect. Fault
diagnosis of the FCL is divided into four stages:
■
check power supply
■
check VCXO and TCXO outputs
■
check signals at TP501 and TP502
■
check VCXO and CODEC circuitry.
The checking of the power supply is given in this section in Task 34 below.
The remaining three stages are covered in “VCXO and TCXO Outputs”
to “VCXO and CODEC Circuitry” respectively. The test and
measurement points for diagnosing faults in the FCL are summarized in
Figure 9.16 .