HP 5065A Operating And Service Manual page 344

Model 5065A
C i r c u i t D i a g r a m s , T h e o r y , and M a i n t e n a n c e
QUARTZ CRYSTAL OSCILLATOR ASSEMBLY
A10 THEORY
GENERAL THEORY
The A10 Oscillator/Divider Assembly (HP Part No.
05065-6094) provides a stable, high-quality 5 MHz signal
at an output level of at least 1 Volt rms into 50 Ohms.
This assembly consists of three subassemblies:
1. AlOAl 10 MHz Quartz Oscillator Assembly
2. A10A3 Power Supply Assembly
3. A10A2 Frequency Divider/Amplifier Assem­
bly.
A10A2 Frequency Divider /Amplifier divides the 10
MHz to 5 MHz and provides the proper output levels.
Electronic Frequency Control (EFC) inputs enable the
oscillator frequency to be adjusted electronically as part
of a servo loop, or by a potentiometer. The entire A10
assembly is designed to replace the 00105-6013 oscillator
formerly used in this instrument.
The AlOAl Quartz Oscillator Assembly (HP Part Num­
ber 10811-60109) is covered by the enclosed 10811A/B
Operating and Service Manual. Circuit board operation
follows:
The 10 MHz output from AlOAl assembly passes
through 10 MHz bandpass filter LI and C5 on A10A3
Power Supply Assembly and then through J l to edge-
triggered D-type flip-flop (A10A2U1) that divides the 10
MHz signal by two. The 5 MHz TTL output at Ul(5)
passes through 5 MHz bandpass filter L7 and Cl 2. The 5
MHz signal is amplified and filtered by emitter-coupled
switch Ql, Q4, and cascade amplifier Q2.
Potentiometer A10A2R8, in the emitter circuit of Ql and
Q4, sets the level at the "5 MHz IV" output to 1.1 Volts
rms into 50 Ohms. The impedance transforming circuit
consisting of C8 and L4 allows Q3 to efficiently drive a
50-ohm external load. Choke L3 provides dc to the
collector of Q3, C9 blocks dc to the 5 MHz output, and L6
provides a dc return for the external load.
Resistive divider A10A2R5, R4 provides a low-level
signal to "5 MHz DIV" output. Nominal voltage at this
point is 70 mV rms into 1000 Ohms.
A +15 Vde reference power supply consists of A10A2CR1,
CR2, and associated parts. This supply provides a stable
reference source for external circuitry connected to the +
or - EFC inputs.
The A10A3 Power Supply Assembly has two inputs;
"20V" and "24V". The"24V" input operates from a
voltage range of +21 to 30 +Vdc from the H P 5065A.
A10U1 regulates this voltage down to +18 Vde used by
oscillator AlOAl oven heater. The +18 Vde is further
regulated to +12 Vde by A10A3U1 for use in oscillator
signal circuits. A10A3CR1, Ql and associated com-
8-50 (SERIES 2120A)
ponents regulate the +12 Vde to +5 Vde for use by the
TTL-divider on A10A2.
Inverting amplifier A10A3Q2 is driven by the "oven
monitor" circuit in AlOAl oscillator assembly. It pro­
vides a n output signal to drive the OSC OVEN meter, or
monitor in the HP 5065A.
Electronic frequency control (EFC) signals from the H P
5065A are summed by A10A3R9, R10, R l l a n d sent to
the EFC input of the oscillator assembly. Factory-
selected resistor A10A3R11 matches the AlOAl oscil­
lator assembly to the parent HP 5065A. If the A10A3
Power Supply Assembly is replaced, the factory-selected
resistor A10A3R11 from the defective board, or a resistor
of equivalent value, must be installed in the new board.
The value of A10A3R11 must equate the value a s noted
on the AlOAl oscillator label itself.
A10 MAINTENANCE
GENERAL
A10 Assembly consists of a factory-selected 10 MHz
oscillator (HP Part Number 10811-60109) and two circuit
board assemblies. A10A2 Assembly divides the AlOAl
10 MHz signal by two and provides buffered 5 MHz
outputs to both the A3 Multiplier and A6 Frequency
Divider assemblies. All input and output connections
are on A10A2. The A10A3 is the power supply for the
AlOAl and A10A2 assemblies. A10A3 provides a n
interface between the 5065A power supplies and the
circuits in assembly A10.
Input and output connections to A10 are as follows: