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Model 5065A
C i r c u i t Diagrams, Theory, and Maintenance
OPERATIONAL AMPLIFIER A9 THEORY
The A9 Assembly amplifies and integrates the output of
A8 Phase Detector and provides a dc error signal for
controlling the quartz oscillator in A10 Assembly. The
front-panel FUNCTION switch provides a means of
opening the control loop by shorting the A9 output to its
input and placing a large resistance in series with the
output.
DC error signals from A8 Phase Detector connect
through pin 14 to the input amplifier U3. U3 is a high-
impedance, low-noise, precision FET input operation
amplifier. It has extremely low input bias current and
low input offset voltage. The integrating function is
provided by C5 with the integrating time constant being
set by the combination of C5 and R5. Initial integrator
drift is minimized by zeroing the input offset voltage of
U3 using potentiometer R8.
U3 output connects to the A14 Logic Assembly as one
logic input and to the CONTROL position of the front-
panel CIRCUIT CHECK switch. The front-panel FUNC
TION switch does two things:
a. In the OPER position, the output of U3 feeds
through R3 to the A10 Quartz Oscillator Assembly
and through Rl to the rear-panel CONTROL jack.
b. In the LOOP OPEN position, the output of U3
connects back to the input, disabling the integra
tor. Additionally, a 100K resistor is placed in series
with the U3 output and the A10 Quartz Oscillator
Assembly input. This resistance helps isolate the
A10 assembly from the A8 Phase Detector Assem
bly.
d. Remove short from pins 14 and 15. Set FUNC
TION switch to LOOP OPEN and connect circuit
as shown:
A9 Test Setup
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2.2M
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A9 (14)
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POWER
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A9 (15)
Set dc voltmeter to 30V range. Observing dc
voltmeter set HP 5065A's FUNCTION switch to
OPER. The voltage will increase at the rate of
about lV/second to about -12V.
Set FUNCTION switch to LOOP OPEN. The
voltage will go to ZERO. Now reverse the battery
or power supply connections so that the negative
terminal is connected to the 2.2 megohm resistor.
Set voltmeter to read positive voltages. Set FUNC
TION switch to OPER and observe voltmeter
reading. Reading should increase at a rate of about
IV per second to a final reading of approximately
+12V.
AS MAINTENANCE
NORMAL OPERATION
The integrating amplifier uses the error signal from the
phase detector as an input and provides the control
voltage for the A10 Quartz Oscillator Assembly. The
output voltage swing is limited to ±12 Vdc.
OPERATIONAL CHECK
a. Remove A8 circuit board from its socket.
h. Remove connection to A9, pins 14 and 15. Remove
dc voltmeter. Reinstall A8 Circuit board. This
completes the check.
ASSEMBLY REPAIR AND REPLACEMENT
After repair or replacement of A9 Assembly, A9R8
should be adjusted as described in OPERATIONAL
CHECK; steps a, b, and c.
b. Short pins 14 and 15 of A9 Assembly and connect a
dc voltmeter to rear-panel CONTROL jack.
c. Set FUNCTION switch to LOOP OPEN and then
to OPER. Measure voltage on dc meter. This
voltage may be drifting, caused by the integrator
circuit integrating the operational amplifier's off
set voltage. If voltage drift exceeds 20 mV/minute,
A9R8 should be adjusted for minimum drift.
8-48
(SERIES 2632A)
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