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THEORY OF OPERATION
POWER SUPPLY
Power Transformer TX201 is designed for use with
120V or 240V A.C. source. The secondary provides
power to bridge rectifier (CR501, CR502, CR503 and
CR504). The positive output of the bridge rectifier
(junction of CR503 and CR504), forms the raw B+
supply (
r-J
20VDC).
Voltage regulation is accomplished in the negative
leg of the power supply through a feedback network
consisting of transistors OX501 and OX502 and their
associated circuitry. The emitter voltage of OX501 is
maintained by diodes CR505, CR506 and CR507. The
base voltage is provided by potentiometer RX506.
If B+ increases, diodes CR505, CR506 and CR507
will draw more current to maintain the emitter volt-
age of OX501. Additionally, the voltage developed
across RX506 will increase, resulting in a higher pos-
itive voltage at the base of OX501 which will result in
less conduction. This reduces the base current of
OX502 since OX501 provides the emitter / base cur-
rent path for OX502. When OX502 conducts less, the
voltage drop across 0502 is increased thus lowering
B+.
If B+ decreases, diodes CR505, CR506 and CR507
will reduce conduction to maintain the emitter volt-
age'of OX501. Additionally, the base voltage provid-
ed by RX506 will decrease. Less voltage on the base
of OX501 will cause it to increase conduction, result-
ing in a greater emitter/base current flow in OX502.
With this condition the voltage drop for 0502 is less
and B+ is increased.
HORIZONTAL
The low-level horizontal section, which consists of
transistors 0101 and 0102 (and associated circuitry),
functions as a variable time delay monostable multi-
vibrator. The input trigger for this circuit is provided
by the horizontal drive pulse. The pulse is injected
into the base or emitter (for either positive or nega-
tive pulse respectively) of 0101 through injection
network C101, C111, R101, R110 and CR101. By vary-
ing the recovery time of the multivibrator, potentiom-
eter R104 adjusts video information position (with re-
spect to raster scan). Output of the
mQnost~ble
mul-
tivibrator, derived at the collector of 0102, is injected
through a coupling network consisting of C110 and
CR103. The resulting "Lock" signal is rereceived by
one side of a precision astable multivibrator at the
4
emitter of 0103. The astable multivibrator circuit is
completed through 0104 and aSSOCiated, circuitry.
This circuit will act as a free running oscillator u,ntil
the "Lock" signal is received from the previous
stage. Once locked, an output pulse is formed at the
emitter of 0104 which is then D.C. coupled to the
base of the horizontal driver transistor, 0105.
Remainder of the horizontal circuit is straightfor-
ward. Features to be noted are: Width and Linearity
Coils L'X102 and LX101 in series with the yoke
(TX202). Linearity is fixed and an adjustable coil is
provided for width. The linearity coil has a magnetic-
ally biased core which makes the inductance of the
coil dependent upon its current. Pincushion and ge-
ometric corrections are made at the factory by the
addition of rubber magnets around the plastic ring of
the yoke. D.C. operation of 12 volts is accomplished
by the (optional) addition of a boost circuit at the hor-
izontal sweep transformer.
VERTICAL
The vertical circuit includes an oscillator conSisting of
transistors 0301 and 0302 and associated circuitry.
Amplification is provided by transistors 0303 and
0304 with the emitter of 0304 feeding the base of the
vertical driver 0305. The vertical output transistors,
Q306 and 0307 are wired in the standard push-pull
configuration. Transistor 0308 doubles B+ during
retrace, maintaining less than 800
IJ.
sec. of retrace
time.
VIDEO
The video amplifier circuit consists of transistors
0401 and 0402 and associated circuitry. The circuit
comprises a cascode amplifier which is triggered by
a positive pulse at pin 8 of the edge connector. Upon
receiving the input pulse, conduction is initiated and
the collector voltage of 0402 is lowered. Amplifica-
tion of low frequency voltage gain is fixed by the ra-
tio of R407 and R408. Gain is maintained to 18 MHz
by the bandwidth enhanCing components R406,
C403, and L401. ReSistors R402 and R403 provide
bias for the amplifier.
The collector output of 0401 is D.C. coupled to the
cathode of the C.R.T. through resistor R201. Raster
cut-off is adjusted with the brightness control R114
which is connected to G1 of the C.R.T.
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