198
Frequency Synthesizer Fault Finding
TM8100/TM8200 Service Manual
© Tait Electronics Limited
June 2006
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:
■
: check loop voltage
■
: VCO fault
■
: check reference voltage
■
: check feedback voltage
■
DIG
SYN
FAST
line
■
TP
503
test point.
The test and measurement points for diagnosing faults concerning the loop
filter are summarized in
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 board from the chassis, remove the
SYN
TOP
can, and place the radio in CCTM.
2.
Remove
R542
(see
3.
Using an oscilloscope, proceed as follows to observe the voltage at
C565
before and after grounding the junction between
C541
and
R547
(see
):
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
. If it is not, the loop-filter
circuitry is suspect; go to
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
):
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
. If it is not, the loop-filter
circuitry is suspect; go to
C565: 13.3
±
0.3 V DC
C565: < 0.5 V DC
Summary of Contents for TM8235
Page 1: ...TM8100 mobiles TM8200 mobiles Service Manual MMA 00005 04 Issue 4 June 2006...
Page 10: ...10 TM8100 TM8200 Service Manual Tait Electronics Limited June 2006...
Page 62: ...62 Description TM8100 TM8200 Service Manual Tait Electronics Limited June 2006...
Page 148: ...148 Disassembly and Reassembly TM8100 TM8200 Service Manual Tait Electronics Limited June 2006...
Page 162: ...162 Servicing Procedures TM8100 TM8200 Service Manual Tait Electronics Limited June 2006...
Page 178: ...178 Interface Fault Finding TM8100 TM8200 Service Manual Tait Electronics Limited June 2006...
Page 258: ...258 Receiver Fault Finding TM8100 TM8200 Service Manual Tait Electronics Limited June 2006...
Page 446: ...446 Spare Parts TM8100 TM8200 Service Manual Tait Electronics Limited June 2006...
