Audio Frequency Phase Error Detector 1A14A3 Circuit Functioning

TM 11-820-695-35

to Z1 signal input port (terminal 1) through terminal E4

and resistor R22. The value of R22 is selected to

2-59.

Audio Frequency Phase Error Detector

provide a minimum if output level. The nominal value

1A14A3 Circuit Functioning (fig. 5-49)

of R22 is 390 ohms.

The, mixer output is an

intermediate frequency in the range from 14.1875 to

a. The 1.5625 kHz reference signal from fixed

23.5625 MHz which is amplified by video amplifiers Q6

frequency divider 1A14A6 is applied through pins P1-2

and Q7 and routed to variable 1 frequency divider

and P1-8. terminals E9 and E10, and resistor R17 to

1A14A4 through transformer T2 and coaxial connector

transformer T1. Diode CR7 prevents spurious signals

P1-A2 (if output).

from being applied to T1. The 1.5625 kHz reference

signal consists of one microsecond positive-going

b. The signal in the secondary of T2 is also

pulses which cause sawtooth generator Q4 to conduct

monitored to provide lamp bias. The signal is rectified

and discharge capacitor C9. The voltage across C9 is

by diode CR6 and the resultant negative voltage keeps

the fundamental sawtooth waveform. A constant current

transistor Q8 nonconducting which holds the transistor in

generator comprised of transistor Q3, resistors R5, R6,

assembly DS1 nonconducting, causing the failure lamp

and R7, capacitor C4, and temperature compensating

DS1 to go off. When the rf output signal amplitude falls

diode CR3, charge C9. The value of R7 is selected at

below 1.8 volts peak-to-peak, the positive bias causes

final test to correctly set the peak amplitude of the

lamp driver Q8 to conduct which in turn causes the

sawtooth and its nominal value is 120k ohms. The

transistor in DS1 to conduct and light the indicator lamp

threshold voltage from which C9 starts charging is the

DS1 (red). Pressing the TEST pushbutton on the main

voltage developed across capacitor C8 which is

chassis applies a 5 volt lamp test signal through pin P1-

determined by the 2 and 2 correction code input

3, terminal E9, and resistor R33, to the base of

signals from the fixed frequency divider which are

lampdriver Q8 causing it to conduct and test that the

applied through pins P1-6 and P1-16, terminals E8 and

lamp circuit is functional.

E7, and resistors R12 and R11 to digital to analog

converter Q9 and Q8, respectively.

The voltage

developed across C8 is determined by the voltage

c. Regulator diode CR5 and resistor R17 reduce

divider consisting of diodes CR4, CR5, and CR6 and

the 28 volt power input to a regulated 6.2 volts for the

resistors R13 through R16. In addition, diode CR4

divide-by-two circuit Q1 through Q3 rf amplifiers Q4,

provides temperature compensation.

The voltage

Q5, and lampdriver Q8.

developed across C8 is the voltage across CR4 and

R13; these form one part of the parallel voltage divider.

d. The 8MHz signal from standard radio frequency

The parallel combination of resistor R14 and R15 in

oscillator 1A14A7 is applied to board 1A14A2A2 (fig. 5-

series with diode CR5 form the second part, and resistor

48) through coaxial connector P1-A3, terminals El and

R16 in series with diode CR6 form the third part of the

E2, an isolation pad consisting of resistors R1, R3, and

voltage divider. When both transistors Q8 and Q9 of

R16, and capacitor C1 to the base of multiply by two

digital to analog converter are nonconducting (2 and 2

transistor Q1. The output from Q1 is doubled to 16 MHz

are both logic zeros), current flows through the three

and doubled again in second stage multiply by two Q2 to

parallel parts of the voltage divider and is maximum.

32 MHz. The output from Q2 is quadrupled by multiply

When 2 is a one level. Q8 is conducting and CR5 is

by four stage Q3 from 32 MHz to 128 MHz. The 128

reverse biased. For this condition, no current flows from

MHz output from Q3 is applied through emitter follower

R15 into R13 causing the voltage across CR4 and R13

Q4 and capacitor C23 to the signal input of the mixer on

to be reduced. When 2is a one level, Q9 is conducting

board 1A14A2A1. The 128 MHz output is developed

and CR6 is reversed biased. For this condition, no

across resistor R15. Rf is filtered from the +28 volt

current flows from R16 into R18 causing

input by rf choke L5 and rf bypass capacitors C11, C16,

and C17.

2-96