TROUBLE-SHOOTING cont.:
LOOP 2
If the fault has been located to LOOP 2 the following hints can be used for
trouble-shooting.
If there is no output signal from the VCXO,
1st LOOP 2 MIXER and LOOP 2 FILTER
on terminal LO 2 OUT, the failure has to be found in the VCXO.
If the output frequency from the VCXO,
1st LOOP 2 MIXER and LOOP 2 FILTER on
terminal LO 2 OUT is lower than 10.008 MHz or higher' than 10.009 MHz, respec-
tively
16.008
MHz and
16.009
MHz,
the phase-locked loop 2 is out of lock.
1.
Set the CLARIFIER to center position and check the output signal from VCXO,
1st LOOP 2 MIXER and LOOP 2 FILTER on terminal FIRST LOOP 2 OUT.
a. If there is no output signal, the failure is in the 1st loop 2 mixer or
that the
10
MHz and/or
16
MHz injection signal is missing.
b. If the output frequency is slightly lower than 8 kHz or slightly higher
than 9 kHz the VCXO, the 1st loop 2 mixer and the
10
MHz and/or
16
MHz
injection signal are apparently ok.
2. Set the CLARIFIER to center position and check the output signal on TPIO
on the CLARIFIER AND 2nd LOOP 2 MIXER, module 1700.
a. If there is no output signal, the failure is on the CLARIFIER AND 2nd
LOOP 2 MIXER circuit board.
b. If the output frequency is lower than 1 kHz or higher than 2 kHz, then
the CLARIFIER AND 2nd LOOP 2 MIXER is apparently ok.
3. Check that the frequency on the phase/frequency detector' IC1013, pin
1
is
100
Hz.
4. Check the LOOP 2 Programmable Divider.
a. If the frequency on terminal LOOP 2 IN, module
1000
is lower than
1
kHz
and the frequency on the phase/frequency detector IC1013, pin 3 is lo-
wer than 100 Hz, the programmable divider is apparently ok.
b. If the frequency on terminal LOOP 2 IN, module
1000
is higher than
2 kHz and the frequency on the phase/frequency detector IC1013, pin 3
is higher than 100 Hz, the programmable divider is apparently ok.
5. Check the phase/frequency detector IC1013.
a. Measure 1.5V DC on terminal PD 2 OUT on the DIVIDER-UNIT.
b. If the input frequency on IC1013, pin 3 is lower than 100 Hz and the
DC voltage on terminal PD 2 OUT is approx. 0.7V, the phase/frequency
detector is apparently ok.
c. If the input frequency on IC1013, pin 3 is higher than 100 Hz and the
DC voltage on terminal PD 2 OUT is approx. 2.3V, the phase/frequency
detector is apparently ok.
6. Check the integrator IC160lb on VCXO,
1st LOOP 2 MIXER and LOOP 2 FILTER.
a. If the DC voltage on TP9 is approx. 0.7V and the DC voltage on output
terminal IC160lb, pin
1
is approx.
17V, the integrator is apparently ok.
b. If the DC voltage on TP9 is approx.
2.3V and the DC voltage on the out-
put terminal of IC160lb, pin 1 is approx.
IV, the integrator is appa-
rently ok.
7. If the failure has not yet been found the summing amplifier IC160la and
the loop filter
Cl614
and R1616 must be checked.
23
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