TROUBLE-SHOOTING cont.:
TROUBLE-SHOOTING IN THE FREQUENCY GENERATING CIRCUIT.
LOOP
1
If the fault has been located to LOOP
1
the following hints can be used for
trouble-shooting.
If there is no output signal from the VCO the fault has to be found in the
VCO-UNIT.
If the output frequency from the VCO is lower than the low frequency limits
or higher than the high frequency limits of the 2 MHz band in question, the
phase locked loop
1
is out of lock. For VCO frequencies look-up the section
PRINCIPLE OF OPERATION.
1. Check the LOOP
1
MIXER output signal on the terminal LOOP 1 OUT, module
1400.
a. If there is no output signal, the failure is on LOOP
1
MIXER, HARMONIC
FILTER UNIT or VCO-UNIT.
b. If the output frequency is approx. 2 MHz or approx. 5 MHz, the VCO-UNIT,
LOOP
1
MIXER and the HARMONIC FILTER UNIT are apparently ok.
2. Check that the frequency on the phase/frequency detector IC1006, pin 1 is
1
kHz.
3. Check the Loop 1 Programmable Divider, module
1000.
a. If the frequency on the input terminal LOOP
1
IN is approx. 2 MHz and
the frequency on the phase/frequency detector IC1006, pin 3 is lower
than
1
kHz, the programmable divider is apparently ok.
b. If the frequency on terminal LOOP 1 IN is approx. 5 MHz and the fre-
quency on the phase/frequency detector IC1006, pin 3 is higher than
1
kHz, the programmable divider is apparently ok.
4. Check the phase/frequency detector IC1006.
a. Measure 1.5V DC on PD 1 OUT on the DIVIDER-UNIT.
b. If the input frequency on IC1006, pin 3 is higher than
1
kHz and the
DC-voltage on PD 1 OUT is approx. 0.7V, the phase/frequency detector
is apparently ok.
C. If the input frequency on IC1006, pin 3 is lower than
1
kHz and the
DC-voltage on PD
1
OUT is approx.
2.3V, the phase/frequency detector
is apparently ok.
5. Check the integrator
ICllOZ
on LOOP
1
FILTER & +18V SUPPLY-UNIT, module
1100.
a. If the DC voltage on PD 1 IN is approx.
0.7V and the DC voltage on out-
put terminal of
IC1102,
pin 6 is approx.
-4V, the integrator
ICI102
is apparently ok.
b. If the DC voltage on PI?
1
IN is approx.
2.3V and the DC voltage on the
output terminal of
ICIIOZ,
pin 6 is approx.
-17V, the integrator
ICI102
is apparently ok.
6. If the failure has not been found yet the
1
kHz loop filter
ICI101
and the
selection circuit for choosing VCO-
and HARMONIC FILTER must be checked.
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