Table of Contents
Advertisement
Model 5065A
Circuit Diagrams, Theory, and Maintenance
AC AMPLIFIER A7 THEORY
A7 Test Setup
THEORY
A low-level signal from A12 RVFR assembly is applied
to A7J1. The input signal to A7J1 contains the ac and dc
components from the photo-detector inside the RVFR.
The fundamental ac signal is 137 Hz and is proportional
to the frequency error. A second-harmonic signal to 274
Hz is also present at A7J1 input.
The preamplifier consisting of Q1, Q2, and IC1 is a low
noise dc amplifier with a zero bias adjustment (A7R3)
A7R3 is adjusted for 0 Vdc bias at A7Q1(B) to minimize
noise on the A7J1 input.
The signal at IC1(6) is sent through a 274 Hz notch-filter
to emitter-follower Q5. The 274 Hz notch-filter, filters
out the second harmonic component, and allows the 137
Hz fundamental signal to pass through to Q5 and IC2.
The amplified output from IC2(6) is routed to A8 Phase
Detector. A portion of the IC2 output is sent through a
137 Hz notch-filter to Q6 and used as feedback to IC2.
A second output from IC1(6) is sent through level adjust
ment A7R29 to IC3. The output from IC3 goes through
the rectifier network and emitter-follower Q9 to A17
terminal board where it may be monitored when M1
meter is in 2ND HARMONIC position.
Feedback around the 2ND HARMONIC amplifier is
through the 274 Hz Notch-filter and Q7. Since the filter
feeds back all frequencies but 274 Hz. The amplifier's
gain is high at 274 Hz and low at all other frequencies.
OPERATIONAL CHECK
NOTE
This check need only be performed if
trouble is suspected in the A7 Assembly.
a. A quick check of the A7 Assembly can be made
by monitoring the output (yellow lead) with an oscil
loscope. Remove the input cable from A7J1 and, using
a small metal tool, touch the center conductor of A7J1.
The "hum signal" thus induced will cause a saturated
signal to appear on the oscilloscope.
This maximum
signal output will peg the CIRCUIT CHECK meter when
switched to 2ND HARMONIC.
b. A more precise test can be made using the fol
lowing procedure.
1)
Set up equipment as shown in A7 Test Setup.
Use Micon-to-BNC test cable that is supplied,
for the connection to A7J1.
2)
Set oscillator frequency to 137 Hz and output
level to .5 V peak-to-peak.
HP204C
OSC
IOM
-vw-
MOUNTED
IN A
SHIELDED
CAN
3)
Connect oscilloscope to A7TP2 or A7WBB.
Output should be about .9 V peak-to-peak.
4)
Connect oscilloscope to A7 output
(Yellow
lead). Signal gain can be varied from zero to
the point where the amplifier clips at about 16 V
peak-to-peak by varying R17. With R17 set for
proper loop gain, the A7 output signal will be
roughly 6-7 times the signal at A7TP2.
5)
Set CIRCUIT CHECK meter switch to 2ND
HARMONIC.
Reduce oscillator output and
allowing for a time lag, note the CIRCUIT
CHECK meter response.
Meter should follow
oscillator level setting. This procedure checks
the second harmonic detector circuit of the A7
Assembly.
6)
Remove the test setup and oscilloscope con
nections.
Using the Micon-to-BNC test cable
provided, connect a dc voltmeter to A7J1. Dc
voltage at this point should not exceed ± 5 mV.
Excessive dc voltage at this point will result in
a noisy solar cell (A12 RVFR Assembly) output.
Adjust A7R3 to bring this voltage below ±5 mV
if required.
7)
Remove test cable and dc voltmeter. Reconnect
cable from A12 Assembly to A7J1.
TROUBLESHOOTING AND REPAIR
a.
If any components in the preamplifier circuit
are replaced, connect a voltmeter to A7Q1 base and
adjust A7R3 for less than 0.5 mV at this point.
b. After any repairs to A7 Assembly, adjust A7R17
as
described
in
Section
5-30,
LOOP
GAIN
ADJUSTMENT.
MODULE REPLACEMENT
If the A7 Assembly is replaced with either a repaired or
new Assembly, set A7R3 as described in the preceding
section TROUBLESHOOTING AND REPAIR. Also per
form adjustments outlined in Paragraphs 5-27 to 5-31.
8-42
Advertisement
Table of Contents
