Circuit Description—475
DC Restorer Circuit
C l 372, C 1371, C R 1377, C R1379, and R1378 form a
DC. restorer circuit. All DC levels in this circuit are
referenced to the negative potential of the CRT cathode.
The voltage difference across R1378 approximately equals
the voltage swing present at the junction of C R 1371 and
C R1373. The control grid end of R1378 is more negative
than the end connected to C R1379. The amplitude of the
voltage swings present at the junction of CR1371 and
C R1373 is determined by the voltage levels established by
the Z-Axis Amplifier and the C RT Bias adjust circuit. The
output level of the Z-Axis Am plifier sets the limit of the
negative excursion (through C R1371) and the Grid Bias
adjust circuit sets the limit of the positive excursion
(through C R1373).
C ALIBR ATO R
General
The Calibrator circuit produces a square-wave output
signal with accurate voltage and current amplitudes. This
output is available as a voltage or current at the C A L I
BRATOR current loop on the instrument front panel. Fig.
3-10 shows a detailed block diagram of the Calibrator
circuit. A schematic of this circuit is shown on Diagram 13
at the back of this manual.
Multivibrator
Q1502 and Q1504 along with their associated circuitry
compose an astable multivibrator. The basic frequency of
the multivibrator is approximately one kilohertz and is
essentially determined by the RC combination of C1505
and R1502. The multivibrator symmetry is set by R1502
and R 1504. Q1502 and Q1504 alternately conduct, pro
ducing a square-wave signal that is taken from the collector
of Q1504.
Output Amplifier
The output signal from the Multivibrator overdrives
Output Am plifier Q1512 to produce a square wave at the
output. When the base of Q1512 goes positive, Q1512 is
cut o ff and the collector level drops down to ground. When
the base goes negative, Q1512 is biased into saturation and
the collector of Q1512 rises positive to about +5 volts.
Amplitude adjustment R1515 adjusts the resistance be
tween the collector of Q1512 and ground to determine the
amount of current allowed to flow , which in turn deter
mines the voltage developed across R 1517.
FAN MOTOR C IR C U IT
General
The fan motor used in the 475 is a brushless DC fan
motor using Hall Effect devices. The fan motor circuitry
varies the rotational speed of the fan with variations in
operating temperature. When the ambient temperature
increases, the value of thermistor R T1696 reduces. This
biases Q1698 on harder to conduct more current through
the Hall devices. Higher currents through the Hall devices
causes the potential difference across them (for instance
between pins 6 and 8 of the fan) to increase. This potential
difference biases one of a pair of transistors on and the
other o ff. For instance, if pin 8 is more positive than pin 6
of the fan, Q 1690A will be on and Q1690B will be o ff. The
higher the potential difference between pin 8 and pin 6 the
harder the on transistor will be conducting. The harder the
transistor is conducting, the faster the fan rotates.
3-20
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 ...
Page 189: ......
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 ...