HP 5065A Operating And Service Manual page 227

Model 5065A
CircuiTOiagrams, Theory, and Maintenance
alignment procedures for the various sections. A 50
MHz oscilloscope, an RF voltmeter, a 50-ohm coaxial
load, and the Micon-to-BNC test cable provided are
required for these adjustments. After initial align­
m e n t and the A3 Assembly reinstalled, the instru­
ment should be completely readjusted as described in
LOOP ALIGNMENT PROCEDURE, Section 5-19.
b. ALIGNMENT OF BUFFER AMPLIFIER
STAGE Q1.
1)
2)
2)
Remove cable from J3. Connect a 50-ohm
coaxial load to J3 using the test cable pro­
vided and connect RF voltmeter to the 50-ohm
load.
Remove shield cover for access to C1, C19,
and C49.
C30,
Adjust C1 for maximum signal at the voltmeter.
There should be two signal peak for a complete
rotation of C1. Tune for the highest peak.
4) Remove voltmeter and test cable from J3 and
reconnect P3 to this jack.
c. ALIGNMENT OF DOUBLER STAGES
Q2 and Q6.
1) Connect oscilloscope to drain of Q6 and adjust
C19 to tune Q2 doubling stage. Select the
higher of the two peaks observed.
2) Connect the oscilloscope to the drain of Q8
and adjust C30 to tune Q6 doubling stage.
Select the higher of the two peaks observed.
3) Ground TP1 to prevent feedback. Then, using
the test cable provided, remove the cable from
J8 and connect a 50-ohm load to this jack.
Connect the oscilloscope to the 50-ohm load.
4) Adjust C49 for maximum scope signal. Re­
move the test cable and reconnect P8 to J8.
5) Readjust C19 and then C30 as described in
steps 1 and 2. C19 and C30 adjustment is
now complete.
d. ALIGNMENT OF Q8TRIPLER STAGE
AND FINAL AMPLIFIER STAGES.
1) Ground TP2 to prevent feedback so that volt­
ages may be monitored within the AGC loop.
2) Remove jumper cable from J8 and use the test
cable provided to connect a 50-ohm coaxial
load. Connect an RF voltmeter to the 50-ohm
load.
3) Sequence through the following adjustments,
each time monitoring the drain (or collector)
of the following stage with an oscilloscope.
In the case of the last stage, Q9, use the RF
voltmeter indication for tuning. Starting with
C49, retune each of these adjustments at least
once:
C18, C33, C46, C49, C52
4) Put the cover on the A3 Assembly and retune
C52, C18, C33, and C46 for a maximum indi­
cation on the RF voltmeter. Note the volt­
meter reading. It should be between 3.2 and
3.6 volts.
5) Remove short from TP2. Voltmeter reading
should drop to 2.7 to 3.0 volts due to the AGC
feedback. Connect a dc voltmeter to TP2.
With the preceeding multiplier adjustments
optimized, this AGC voltage should be about
4.5 volts.
6) Remove the test cable and reconnect the
jumper cable to J8.
e. A3 MATCHING NETWORK ADJUSTMENTS
The matching network adjustments are as follows:
R40 This control sets bias for the step-recovery
diode in the A12 Assembly.
C59, C61, and L25 These adjustments match the
multiplier output to the load presented
by the step-recovery diode circuit in the
A12 Assembly.
The matching network adjustment must be aligned with
the A3 Multiplier installed in the system. See Section
5-25, RF ALIGNMENT under LOOP ALIGNMENT PRO­
CEDURE for adjustment instructions.
MODULE REPLACEMENT
When replacing the A3 Assembly after repair or when
a new A3 Assembly is installed, the instrument should
be completely realigned per Section 5-19, LOOP ALIGN­
MENT PROCEDURE.
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