Atec Tektronix-1502 - Manual (Page 34)

TM 9-4935-601-14-3&P
Gain Amplifier. The Gain Amplifier consists of U2143 with variable gain provided by R0263. The
incoming voltage is attenuated approximately 20% by R2228 and R2144. The output voltage is approximately
200 mp per division. The variable gain control has a range of approximately 5 times and is set by the values of
R0263 and R2142. The output goes through the Retrace Logic to the Vertical Output Amplifier.
Retrace Logic (Schematic 4). The Retrace Logic consists of gate U3123C, inverter Q3137, oscillator
U3123A and U3123D, and analog switches U3223C and U3223D.
The only time the vertical signal is applied to the vertical output amplifier is during the forward scanning
cycle. During the retrace cycle, an offset voltage is applied to the vertical output amplifier.
During the slow ramp forward scan cycle, the retrace signal is negative, as is pin 2 of U3123A. This causes
the output of U3123D to be low. Pin 6 of U3223C is also high and the vertical signal is passed through the
analog gate to the output amplifier.
During the retrace cycle, the output of U3123D is high, but pin 6 of U3223C is low and pin 12 of U3223D is
high. This allows the output of U3123D to be passed to the vertical output amplifier, which causes the beam to
be deflected below the crt viewing area.
Vertical Output Amplifier. The Vertical Output amplifier consists of Q3236, Q3232, Q3139, and Q3235.
The mode of operation is identical to that of the Horizontal Output Amplifier. In the Vertical Output Amplifier,
the amplifier gain is approximately 80. Capacitor C3233 is added to increase high frequency response.
CRT Display Circuits (Schematic 4)
The crt display circuit High Voltage Supply provides the voltage for the FOCUS control, INTENSITY
control, and the cathode of the crt and the crt biasing network. The crt provides a display of the conditions of
the cable being checked and is also shown in the circuit.
High Voltage. The high voltage circuit consists of: an oscillator, formed by transistors Q4149 and Q4145;
transformer T4141; a high voltage multiplier circuit consisting of CR4323, CR4313, CR4311, and CR4211, and
a resistor divider string consisting of R4114, R4126, R4222, R4129, and R4221, INTENSITY control R0442,
and FOCUS control R0432.
The self-starting oscillator is formed by R4146, R4141, and transformer T4241. The transformer has a
separate feedback winding (pins 9, 10, 11), which ac couples the voltage to the bases of the transistors (Q4149
and 04145). R4146 and R4141, along with the 0.001
µ
F capacitors (C4135 or C4134), establish a time-
constant that prevents saturation and controls the oscillator frequency.
Winding 7-8 of the transformer provides a 0.6 volt rms signal for the crt filament. This winding is high
voltage insulated. Winding 4-6 provides a 500 volt square wave that is used to generate the high voltage. The
high voltage multiplier circuit converts the 500 volts to 2000 volts. A resistor divider string is connected
between the 2000 volt and the 1000 volt taps of the multiplier circuit. This provides the voltages for correct
biasing of the crt. The FOCUS and INTENSITY controls are included in this divider string. A 150 volt zener
diode, VR4117, is used to stabilize the cathode voltage.
Cathode-Ray Tube. In order to optimize the crt display, internal controls for Astigmatism, Geometry, and
Trace Rotation are provided. These controls, which are located on the output board, are: R3148, R3149,
R3242 (ASTIGMATISM); R3249, R3248 (GEOMETRY); and R3142, R3143 (TRACE ROTATION).
Power Supply (Schematic 6)
The Power Supply consists of a line selector, transformer T0389, a battery charger network, battery pack
BT0369, and the dc voltage converters. The battery charger network contains SCR switch Q6155, SCR
triggering circuit Q6143, Q6244, and Q6241, operational amplifier U6138, and the current reference resistor
R6131.
In the dc voltage converters, there is an Anti-Deep Discharge circuit, Q6548, Q6549, and Q6547; a primary
regulator, Q6552, Q6557, and VR6459; a controllable oscillator, Q6458, Q6445, C6551, R6545; a fly-back
switch, Q6435 and Q6349; and fly-back transformer T6535. The secondary output windings of T6535 provide
the +165 V, +100 V, +25 V, +10 V, +8 V, -8 V, +5 V, and -5 V supplies. The +10 V, +5 V, and -5 V circuits
have secondary regulation circuitry. See Fig. 3-6 for a simplified block diagram of the power supply.
Line Selector. The line selector is composed of the input transformer's terminals and can be wired for
either 110 volts or 220 volts. It is factory wired for 110 volts. If 220 volt operation is required, remove the wire
straps from lugs 1-2 and 3-4 of T0389; then connect a strap from lug 2 to lug 3.
REV B FEB 1980
3-9