Tait TM8100 mobiles, Service Manual

Page: 187 / 620

TM8100/TM8200 Service Manual Frequency Synthesizer Fault Finding 187
© Tait Electronics Limited November 2007
Transmit and
Receive Faults
A transmit or receive fault will be implied by one of the following
consequences:
■
radio fails to receive or receive performance is degraded
■
radio fails to enter transmit mode
■
radio exits transmit mode unexpectedly
■
radio enters transmit mode but fails to transmit
■
radio enters transmit mode but transmit performance is degraded.
With a fault of this kind, neither of the initial tasks is required.
Fault diagnosis should begin with
“Power Supplies” on page 189 .
Summary
To summarize, given the nature of the fault, proceed to the task or section
indicated below:
■
Task 1 : system error
■
Task 2 : lock error
■
“Power Supplies” : transmit or receive fault.
The checks of Task 1 and Task 2 will indicate the section with which the
fault diagnosis should continue.
Task 1 —
System Error
A system error indicates a fault in the calibration of either the FCL or the
frequency synthesizer. To determine which is faulty, calibrate the VCXO
and the transmit VCO as described below. (Always calibrate the former first,
because the latter depends on the former.)
1. Place the radio in CCTM.
2. Enter the CCTM command
301 0 10
to calibrate the VCXO.
The response will be one of the following three messages:
■
“passed sanity check. Cal’d values put into effect”
■
“failed sanity check. Cal’d values not in effect”
■
“Cal failed: lock error”.
The first two messages will be preceded by four calibration values.
3. In the case of the first message (passed), go to Step 4 . In the case of
the second and third messages (failed), the FCL is suspect; go to
“Power Supply for FCL” on page 234 .
4. Enter the CCTM command
302 0 10
to calibrate the transmit VCO.
The response will be one of the three messages listed in Step 2 .
The first two messages will be preceded by eight calibration values.
Reset the radio and re-enter CCTM.
5. If the calibration succeeded but the system error persists, replace the
board and go to
“Final Tasks” on page 163 . In the case of the second
message (failed sanity check), go to Step 6 . In the case of the third
message (calibration failed), go to Step 8 (UHF radios) or “Power
Supplies” on page 189 (VHF radios).