TM9100 Service Manual
Frequency Synthesizer Fault Finding
187
© Tait Electronics Limited
August 2005
9.4
Loop Filter
Introduction
If the power supplies for the frequency synthesizer are correct, and the PLL
is functioning properly, check the loop filter next:
■
Task 11
: check loop voltage
■
Task 12
: VCO fault
■
Task 13
: check reference voltage
■
Task 14
: check feedback voltage
■
Task 15
: check
DIG
SYN
FAST
line
■
Task 16
: check
TP
503
test point
The test and measurement points for diagnosing faults concerning the loop
filter are summarized in
Figure 9.5
.
Task 11 —
Check Loop Voltage
Check whether the loop filter is functioning correctly by measuring the
loop voltage at the output of the filter at C565.
1.
If not already done, remove the main-board assembly from the
chassis, remove the
SYN
TOP
can, and place the radio in CCTM.
2.
Remove R542 (see
Figure 9.7
).
3.
Using an oscilloscope, proceed as follows to observe the voltage at
C565
before and after grounding the junction between C541 and
R547
(see
Figure 9.7
):
While holding the oscilloscope probe at C565, use a pair of tweezers
to momentarily ground the junction. The voltage should change to
the following value (if it is not already at this value):
4.
If the loop voltage is correct, go to
Step 5
. If it is not, the loop-filter
circuitry is suspect; go to
Task 13
.
5.
Proceed as follows to observe the voltage at C565 before and after
applying 3 V DC to the junction of C541 and R547; there is a
convenient 3 V level at R544 (see
Figure 9.7
):
While holding the probe at C565, use the tweezers to momentarily
apply 3 V DC to the junction; do not touch the board with your
hand, and do not allow the tweezers to touch any cans when you
remove them. The voltage should change to:
6.
If the loop voltage is correct, go to
Task 12
. If it is not, the loop-filter
circuitry is suspect; go to
Task 13
.
C565: 13.3
±
0.3 V DC
C565: < 0.5 V DC
Summary of Contents for TM9100
Page 1: ...TM9100 mobiles Service Manual MMA 00017 01 Issue 1 August 2005 ...
Page 4: ...4 TM9100 Service Manual Tait Electronics Limited August 2005 ...
Page 10: ...10 TM9100 Service Manual Tait Electronics Limited August 2005 ...
Page 22: ...22 Introduction TM9100 Service Manual Tait Electronics Limited August 2005 ...
Page 62: ...62 Description TM9100 Service Manual Tait Electronics Limited August 2005 ...
Page 96: ...96 TM9100 Service Manual Tait Electronics Limited August 2005 ...
Page 138: ...138 Disassembly and Reassembly TM9100 Service Manual Tait Electronics Limited August 2005 ...
Page 152: ...152 Servicing Procedures TM9100 Service Manual Tait Electronics Limited August 2005 ...
Page 168: ...168 Interface Fault Finding TM9100 Service Manual Tait Electronics Limited August 2005 ...
Page 244: ...244 Receiver Fault Finding TM9100 Service Manual Tait Electronics Limited August 2005 ...
Page 396: ...396 CODEC and Audio Fault Finding TM9100 Service Manual Tait Electronics Limited August 2005 ...
Page 420: ...420 Fault Finding of Control Head TM9100 Service Manual Tait Electronics Limited August 2005 ...
Page 426: ...426 Spare Parts TM9100 Service Manual Tait Electronics Limited August 2005 ...
Page 430: ...430 TM9100 Service Manual Tait Electronics Limited August 2005 ...
Page 444: ...444 TMAA04 05 Ignition Sense Kit TM9100 Service Manual Tait Electronics Limited August 2005 ...
Page 448: ...448 TMAA10 01 Desktop Microphone TM9100 Service Manual Tait Electronics Limited August 2005 ...