HP 5065A Operating And Service Manual page 299

Set scope sweep to 2 msec/cm and vertical
sensitivity for 50 mV/cm. Adjust scope for
external sync from signal at A8TP2.
Tune OSC FREQ ADJ COARSE for a signal
indication on scope. The normal indication as
the oscillator is tuned through the RVFR
resonance is the appearance of a 137 Hz sine
wave; it will increase and then decrease in
amplitude, and become 274 Hz at a lower
amplitude. It will then become 137 Hz which
will again increase and then decrease in
amplitude and disappear. If there is no signal
go to step 5. Tune the oscillator for maximum
undistorted 274 Hz signal, and set CIRCUIT
CHECK meter to 2ND HARMONIC. If reading
on meter is significantly below that which is
normal for the instrument, the instrument
should be completely realigned as described in
LOOP ALIGNMENT PROCEDURE of Section
5-19.
If signal on scope as noted above (or 2ND
HARMONIC as noted on front panel meter) is
excessively noisy, the signal-to-noise ratio of
RVFR should be rechecked as described in
Section 5-26 of the instrument alignment pro­
cedure. If signal-to-noise ratio is not above
250, the RF alignment should be checked per
Section 5-25 of the instrument alignment pro­
cedure. The signal-to-noise ratio should then
be rechecked. If the signal-to-noise ratio is still
less than 250, the RVFR should be replaced.
Even with a signal-to-noise ratio of less than
250, the instrument will remain on frequency;
however, the short term stability of the instru­
ment will be out of specifications.
If no signal was observed in step 3, it indicates
trouble in one of several places:
(a) Preamplifier in A7 Assembly not working.
(b) RF output from A3 Assembly low in am­
plitude or pi-matching network mistuned.
(c) A1 Synthesizer output off frequency or too
low in amplitude.
(d) No 137 Hz modulation from A8 Assembly.
(e) Defective RVFR.
Items (a) through (d) can be easily checked by
referring to the individual maintenance
sections. If these circuits are OK, it indicates
that the RVFR is probably defective and should
be replaced. To check these circuits proceed
as follows:
(a) With the instrument set up as shown in the
RVFR test setup illustration and oscillo­
scope setup per preceding step c(2), remove
plug A7P1. Touch the center conductor
of A7J1 with a small piece of metal such
Model 5065A
Circuit Diagrams, Theory, and Maintenance
as a piece of solder. A large signal should
appear on the scope. This indicates the
preamplifier is OK.
(b) Check RF output of A3 Multiplier Assembly
by following procedure in the A3 Oper­
ational Check.
(c) Check amplitide and frequency of synthe­
sizer output at end of cable at A3P5. Am­
plitude should be approximately 100 mV
and the correct frequency can be found in
Table 3-6 after noting Thumbwheel and
slide switch settings on the A1 Assembly.
(d) Remove A3P1 and measure the 137 Hz
modulation signal present at the end of the
cable at A3P1. If signal OK at this point re­
move and disassembly A3 Assembly.
Check diodes A3CR3, 4, 5, and 6. Recon­
nect cable to A3J1 and +20 V(R). Check
signal at CR3 (anode).
7) If all tests to this point are OK, the RVFR is
probably defective and should be replaced.
A12 RVFR ASSEMBLY REMOVAL
AND REPLACEMENT
a. Disconnect all external power sources including
batteries.
b. Remove top and bottom instrument covers.
c. Disconnect RVFR cable from A3J4 on Multiplier
Assembly A3.
d. Disconnect RVFR cable from A7J1 on AC Ampli­
fier Assembly A7.
e. Locate the twisted pair of black and red wires
from the RVFR Assembly. Disconnect the red wire at
socket XA4 pin 1 and the black wire at XA8 pin 1.
NOTE
DO NOT disconnect the diode con­
nected between XA4(1) and XA8(1).
f. Disconnect A12J15 and A12J16 from chassis
plugs.
g. Remove four nuts and lockwashers holding the
RVFR unit in place and withdraw the assembly from the
top of the instrument.
NOTE
When packing for return to the factory,
pack carefully for maximum shock
cushioning and label shipping package
"FRAGILE". If possible, use packing
from replacement RVFR unit.
h. Handle replacement RVFR assembly carefully
while unpacking and installing. Note two resistors pack­
aged with this Assembly. These are the calibration resis­
tors for the A11 Temperature Regulator Assembly and are
required to provide proper operating temperatures for cell
and lamp areas of the replacement A12 RVFR Assembly.
Install the A12 Assembly in the reverse order of the above
removal steps, making sure the four lock washers are in
place.
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