HP 5065A Operating And Service Manual page 207

Model 5065A
Circuit Diagrams, Theory, and Maintenance
A1Y1, A1L1, A1L2, A1L3, or A1L4 CHECK AND
REPLACEMENT
a. Set FUNCTION switch at LOOP OPEN.
I. When frequency at HI and LO settings are cor­
rect, turn off electrical power, disconnect the syn­
thesizer, replace its cover, and then replace the
Synthesizer in the 5065A unit.
b. Remove synthesizer assembly from instrument
(see Troubleshooting). Remove module cover. Dis­
connect electrical power and turn the unit over. Using
a piece of insulation to prevent shorts, reconnect the
Synthesizer 5 MHz input to A1J2, the +20 volt lead
(wht-red), to the appropriate jack and circuit board
ground to chassis ground. Reconnect electrical power.
m. Reconnect all Synthesizer electrical connec­
tions, apply electrical power.
n. Connect the 5065A as shown in the following
illustration and check Synthesizer output frequencies as
described in the Performance Check for A1 Synthesizer.
c. Remove Crystal Y1 and, using a high-imped­
ance voltmeter, check voltage at junction of CR27 and
R79. It should be 6 V ± 0.5 volts dc. If it is not, check
bias circuitry: R71, R72, CR32, CR30, R73, Q23,
CR27, etc. If there are no defective components, adjust
R71 for the correct voltage.
d. Disconnect 5 MHz from A1J1 and replace Y1
in its socket.
e. Set TIME SCALE slide switch on synthesizer
toLO.
f. Measure Synthesizer frequency at A1J3 using
setup shown in the following illustration.
Figure 2.
L_
F R E
_°_J
5MHz
TEXT STD~!
HP5065A
UNDER TEST
i
1
[SYNTH 1
J
1
ELECTRONIC
COU YTER
RF
VOLTMETER
g. If counter indication is greater than 5.314850
MHz or less than 5.314550 MHz, replace A1Y1 before
proceeding.
h. Adjust L1 and L2 as necessary for a counter
indication of 5.315700 + 50 Hz.
i. Set TIME SCALE slide switch on Synthesizer
to HI.
j . Adjust L4 as necessary for a counter indication
Of 5.315000 + 50 Hz.
k. Set TIME SCALE slide switch on Synthesizer to
LO. Check that counter indication is 5.314700 ± 50 Hz.
If frequency is incorrect, repeat steps g through j .
PHASE LOCKED VOLTAGE CONTROLLED
OSCILLATOR
The phase locked voltage controlled oscillator produces
the 5.315...MHz signal applied (through A3 Multiplier)
to the harmonic generator/step-recovery diode in A12
Assembly. In A12, 5.315...MHz is mixed with the
6.840...GHz phase-modulated signal (the 114th har­
monic of 60 MHz). Oscillator frequency is determined
by the bias voltage applied to varactor diode CR27.
The figure below illustrates the sampling process.
The 5 MHz/n output pulse of the preset divider is the
sampling pulse in the phase lock sampling circuit. The
sampled output pulses of this circuit are integrated by
the circuit time constant to a dc voltage representing a
phase error. This dc voltage acts on CR27 to shift oscil­
lator frequency for a zero dc output which corresponds
to a phase-locked, "on frequency" condition.
Sampling Process
5 M H z / N
.08 LISEC SAMPLING
PULSES FROM PRESET
DIVIDER
5.35 MHz
SAMPLED
5 . 3 5 . . . . MHz SAMPLED
APPROXIMATELY EVERY
10,000 CYCLES I
^-_ SAMPLED PULSE
AVERAGE DC LEVEL
APPLIED TO CR27 TO
CONTROL THE 5 . 3 1 5 . . . . M H z
OUTPUT
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