Circuit Description—475
Chop Blanking Amplifier
The Chop Blanking Am plifier Q348 provides an output
pulse to the Z Axis Am plifier circuit, which blanks out the
transitions between the Channel 1 and Channel 2 traces
when operating in the CHOP mode. The inherent pro-
pogation delay of inverters U 340A , U340B, and U340C are
used to provide some signal delay to the chop blanking
signal. This allows the blanking signal and the channel
switching transient to arrive in the CRT simultaneously.
Channel 2 Signal Output Amplifier
Q420 and Q430 compose the Channel 2 Vertical Signal
Output Amplifier. A sample of the Channel 2 signal from
pin 5 of Channel Switch 1C U 370 is amplified and inverted
by Q420. CR422 provides thermal compensation for the
base-emitter junction of Q 420. Common-base amplifier
Q430 provides the final amplification and isolates the
output from the internal amplifier circuitry. Output im
pedance of the amplifier is equal to the parallel combina
tion of R431 and R432 (approximately 50 ohms).
Normal Trigger Pickoff Amplifier
The trigger signal for NORM trigger operation is ob
tained from a sample of the vertical deflection signal that is
available from pin 15 of U 370. Normal Trigger DC
Adjustment R425 sets the DC level of the normal trigger
output signal so that the sweep is triggered at the 0 level of
the displayed signal when the Triggering LEV E L control is
set to 0. Q390 and Q 396 are connected as a non-inverting
feedback amplifier. Gain of the stage is approximately:
■fl»2,+,R3ai-
R392
Scale-Factor Switching Circuits
The vertical deflection factor for each channel is
indicated by back-lighting the appropriate figures imprinted
on the flange of each V O L T S /D IV knob. For purposes of
explanation, only the circuit action of the Channel 1
Scale-Factor Switching Circuit is discussed. When a X I
probe is connected to the CH 1 OR X input connector, the
base level of Q312 is drawn positive by R316 toward the
collector level of Q314. Q314 conducts heavily through X I
display factor bulb DS314 and Q312 is turned o ff.
Therefore, the X I display factor bulb is on and the X 1 0
display factor bulb is off.
When a X 1 0 probe with a scale factor switching
connector is attached to the CH 1 OR X input connector,
the base of Q312 is grounded through R311. Now, Q312
conducts very heavily through X 1 0 display factor bulb
DS312. The positive level at the collector of Q312 turns
Q314 off (through the divider R313-R314); the X 10
display factor bulb is on and the X I display factor bulb is
off.
V E R T IC A L OUTPUT A M P LIFIE R
General
The Vertical Output Amplifier provides the final amplifi
cation for the vertical deflection signal. This circuit includes
the BEAM F IN D function. The BEAM F IN D pushbutton,
when pressed, compresses an overscan display to within the
C RT viewing area. A schematic of the Vertical Output
Amplifier is shown on Diagram 4 at the rear of this manual.
First 1C Amplifier
The first amplifier stage in the Vertical Output Amplifier
is integrated circuit U 450. U 450 is basically an emitter-
coupled, push-pull, cascode amplifier cell. Biasing is ar
ranged so that there is no phase-inversion through the stage.
The signal from the delay line is applied to the amplifier
through C 441, L441, L442, C445, L445, and L 444. These
inductances and capacitances are part of the etched runs of
the circuit board and provide some high-frequency peaking
by forming a T-coil circuit without mutual coupling. Most
of the components connected between pins 2 and 3 of
U450 provide high-frequency compensation of the stage.
RT452 varies in value with variations in ambient tempera
ture to compensate for associated changes in amplifier gain.
The BEAM F IN D pushbutton, when pressed, removes —8
volts from the top of R459. This reduces the dynamic
swing capabilities of the stage to limit the display on the
C RT to within the viewing area. The gain of the Vertical
Output Am plifier section is adjusted in this stage by
adjusting Vertical Output Gain R449.
Second 1C Amplifier
The second amplifier stage in the Vertical Output
Amplifier is integrated circuit U 470. U 470 is a multi-stage
cascode amplifier cell. The input signal is applied to pins 1
and 5 with the inverted output signal taken from pins 9 and
12. Pins 2 and 4 are emitter connections. Some of the
components connected between pins 2 and 4 provide
slower time constants to compensate for signal rolloff that
occurs in the delay line, while the remaining components
compensate for thermal considerations in the stage. The
Output Bias adjust (R487) sets the DC levels within the
stage to optimize the operating performance of U 4 7 0 .T h e
output signal from U 470 connects directly to the deflection
plates of the C RT.
A TRIG G ER GENERATOR
General
The A Trigger Generator circuit produces the trigger
pulse used to start the Sweep Generator circuit that
provides the A portion of the CRT display. The trigger
pulse is derived from the internal trigger signal from the
vertical deflection system, an external signal connected to
3-7
Summary of Contents for 475
Page 6: ...475 475 Oscilloscope ...
Page 20: ......
Page 46: ......
Page 151: ...A B C D E F G Fig 7 4 P 0 A4 Vertical Mode Switch circuit board ...
Page 152: ...n m m m 1 t siumm c ii im ...
Page 154: ...Diagrams 475 A B C D E F G ...
Page 155: ...GRID LOCATOR Fig 7 8 P O A3 Vertical Preamp circuit board ...
Page 157: ...Diagrams 475 ...
Page 158: ...GRID LOCATOR 2 3 4 5 6 7 8 9 1 10 11 1 12 Fig 7 10 P 0 A3 Vertical Preamp circuit board ...
Page 160: ...Diagrams 475 GRID LOCATOR Fig 7 11 A5 Vertical Output circuit board ...
Page 163: ...Diagrams 475 GRID LOCATOR Fig 7 12 P O A8 Trigger Generator And Sweep Logic circuit board ...
Page 167: ... 415 OSCILLOSCOPE B T R IG G E R G E N E R A T O R g B TR IG G E R GEN ER A TO R ...
Page 168: ...Diagrams 475 GRID LOCATOR ...
Page 172: ...SWEEP G E N ER A TO R S ...
Page 175: ...TIM IN G HORIZONTAL DISPLAY SWITCHING ...
Page 177: ...A 011 HORIZONTAL AMPLIFIER 8 l j k J Ll J Ol Z o N C O X U 1 C L O o v O o _J V v P O in r ...
Page 179: ... 476 OSCILLOSCOPE ...
Page 180: ...POWER SUPPLY ...
Page 182: ...CRT CIRCUIT ...
Page 185: ...C A L IB R A T O R A N D F A N C I R C U I T 4 C A LIB R A TO R FAN MOTOR C IR C U IT ...
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Page 190: ...4 T 475 OSCILLOSCOPE FIG 1 FRO NT PANEL ...
Page 191: ...475 OSCILLOSCOPE FIG 2 MAIN FRAME ...
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Page 200: ...FIG 3 RIGHT SIDE l 475 OSCILLOSCOPE ...
Page 201: ...V S X O t l B O T T OVJ 8 8 ...
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Page 210: ...5 ...
Page 211: ...4 4 75 O S C ILLO S C O P E FIG 5 CAB IN ET ...
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Page 241: ... 1 I R I II9A po S IT I o n f i n e I R l 130 PAGE 4 OF 5 R 1234 Ml 9 91 9 473 ...