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Model 5065A
Circuit Diagrams, Theory, and Maintenance
OPERATIONAL AMPLIFIER A9 THEORY
OPERATIONAL CHECK
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
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.
In
addition to the integrating feedback, an amplitude-
limiting feedback signal prevents saturation of A9
amplifier circuits.
Dc error signals from A8 Phase Detector connect
through pin 14 to Q1A, B input amplifier.
This FET
amplifier stage provides a high-impedance input and
push-pull
outputs to
differential
amplifier
AMPL1.
Balancing adjustments are:
Integrator Zero Coarse
Adjustor R3 and Integrator Zero Fine Adjustor R10.
Zener
diode
CR1
provides
regulated
10 volts for
AMPL1. Further dc amplification is handled by Q2 and
Q3.
Diodes CR6 and 7 provide the proper operating
voltage for Q3. The integrating function is provided by
C3 (Q3 output connects through C3 to Q1A input).
Output signals in excess of ±14 volts feed back through
reverse connected clamping Zener diodes CR8 and CR9.
That portion of the signal in excess of ±14 volts is fed
back to the input at Q1 base to limit signal amplitudes
in the A9 circuits, thus providing the A9 circuits with
fast overload recovery.
The feedback signal routes
through the diode network of CR2, 3, 4, 5. These diodes,
series connected for each
polarity, give
isolation
between input and output when no overload signal is
present.
Q3 output connects to the A14 Logic Assembly as one
logic input and to the CONTROL position of the
CIRCUIT CHECK switch. The FUNCTION switch does
two things:
a.
In the OPEN LOOP position, Q3 output is
shorted to Q1A input for unity gain and R5 (100K) is
inserted between Q3 output and A10 input to further
attenuate the signal.
b.
In the OPER position, Q3 output feeds through
R23 and CR10 which limits positive signals to the range
of zero to +7 volts.
This signal routes through the
FUNCTION switch to the quartz oscillator control cir
cuit in A10 Assembly. This output also connects to the
rear-panel CONTROL jack.
a.
Remove A8 circuit board from its socket.
b. Short pins 14 and 15 of A9 Assembly and con
nect 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 Integrating Amplifier
integrating its internal zero offset.
If voltage drift ex
ceeds 20 mV/minute, A9R3 and R10 should be adjusted
for minimum drift.
d.
Remove short from pins 14 and 15. Set FUNC
TION switch to LOOP OPEN and connect circuit as
shown:
A9 Test Setup
- »
2 . 2 M
- V W
- * -
A9 (14)
I T0I.5VDC
- L
BATTERY O R ~ = T
POWER
SUPPLY
■
»
- » -
A9 (15)
e. Set dc voltmeter to 30 V range. Observing dc
voltmeter set FUNCTION switch to OPER. The voltage
will increase at the rate of about 1 V/second to about
-14 V.
f.
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.
g.
Set voltmeter to read positive voltages.
Set
FUNCTION switch to OPER and observe voltmeter
reading. Reading should increase at a rate of about 1 V
per second to a final reading of approximately +7 V.
A9 MAINTENANCE
NORMAL OPERATION
h.
Remove connection to A9, pins 14 and 15.
Remove dc voltmeter.
Reinstall A8 Circuit board.
This completes the check.
The integrating amplifier uses the error signal from the
phase detector as an input and provides the control
voltage for the Quartz Oscillator Assembly A10.
The
output voltage swing is clamped between -14 Vdc and
+7 Vdc.
ASSEMBLY REPAIR AND REPLACEMENT
After repair or replacement of A9 Assembly, A9R3 and
A9R10 should be adjusted as described in Operational
Checks a, b, and c.
8-48
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