190
Diagnosis of Faults on Main Board
TM8100 Mobile Radio
Service Manual
May 2004 © Tait Electronics Limited
Task 4 —
Incorrect VCO Tuning
Voltages
If the VCO tuning voltages are incorrect, rectify the fault as follows:
1.
Remove the
SYN
TOP
and
SYN
BOT
cans.
2.
There are two basic faults: Firstly, the VCO tuning voltage at
C565 is low, whereas the voltage at pin 7 of IC505 is much higher;
in this case go to Step 3. Secondly, the tuning voltage is either
near 0 V or near the VCL supply voltage measured in Step 3 of
Task 1; in this case go to Step 4.
3.
Check for damage, shorts, open circuits, and dry solder joints in
the circuitry along the path between pin 7 of IC505 [at 5J5/5F8]
and C565 [at 5M5/5F11] (see
). If a
fault is found, repair it, confirm the removal of the fault, and
return to
. If the repair failed or the fault could not
be found, return to
and replace the complete
main-board assembly.
4.
Check for open circuits, short circuits, and faulty components in
the circuitry in the feedback path for the operational amplifier
IC505 [at 5J5/5F8] (Q511, IC504, R554, R556, C548, C555)
(see
). If no fault is found, go to Step
5. If a fault is found, repair it, confirm the removal of the fault,
and return to
. If the repair failed, return to
and replace the complete main-board assembly.
5.
Check the reference input signal at pin 8 of IC503 [at 5H7] of the
PLL (see
). The signal should be about 13 MHz and
1 V
pp
. If it is, return to
and replace the complete
main-board assembly. If it is not, go to Step 6.
6.
Remove IC503. Repeat the above check of the reference input
signal. It should now be about 1.5 to 2.0 V
pp
. If it is not, the FCL
requires investigation; go to
. If it is, replace IC503,
confirm the removal of the fault, and return to
the repair failed, return to
and replace the
complete main-board assembly.
Содержание TM8000 Series
Страница 32: ...32 Introduction TM8100 Mobile Radio Service Manual May 2004 Tait Electronics Limited ...
Страница 78: ...78 Circuit Descriptions TM8100 Mobile Radio Service Manual May 2004 Tait Electronics Limited ...
Страница 106: ...106 General Information TM8100 Mobile Radio Service Manual May 2004 Tait Electronics Limited ...
Страница 124: ...124 Servicing Procedure TM8100 Mobile Radio Service Manual May 2004 Tait Electronics Limited ...
Страница 164: ...164 Servicing of Control Head TM8100 Mobile Radio Service Manual May 2004 Tait Electronics Limited ...
