Q1091, and Q1094 and th eir associated circu itry make up a
damper circu it designed to suppress this ringing.
When the Turn On c ircu it generates the turn-on pulse for
Q1080, the negative movement at the collector o f Q1064 is
coupled through C1093, CR1092, and R1095 to the base
of Q1091. The resultant narrow negative-going pulse at the
base o f Q1091 starts to turn o ff Q1091 and Q1094. The
positive movem ent at the collector o f Q1065 is also
coupled back to the Damping C ircuit and applied to the
base of Q1090 through CR1090 and R1090. Q1090 turns
o ff, and its collector goes negative, which serves to hold
Q1091 and Q1094 off.
When Q1080 is turned o ff, its collector steps positive to
a level determined by the clamping action of V R1085 and
VR1084. T1085 transform s this into a negative movement
at the cathode of CR1091 to hold Q1091 and Q1094 o ff.
The negative movement at the collector o f Q1065 is applied
to the base of Q1090 through CR1090 and R 1090, turning
Q1090 on. A bo ut five to ten microseconds after the tu rn
o ff time of Q1080, flyback ends, ringing occurs in T 1085
and CR1091 turns off. Q1091 and Q1094 are turned on by
Q1090 and conduct very heavily through the full-wave
bridge rectifier CR1096-CR 1099 and one w inding of T 1085
to reduce the amplitude o f the ringing. The damping tran
sistors Q1091 and Q1094 thus conduct only during the
tim e flyback ringing is occurring.
C1095, CR1095, and the transform er winding connected
to the cathode of CR1095 form a half-wave rectifier power
supply generating approxim ately —5 volts to be used in the
Damping Circuit.
Regulator C ircuit
The Regulator C ircuit holds the outputs of the Power
Supply relatively constant despite variations in input line
voltage, line frequency, and load demand. Regulation is
accomplished by varying the tim e interval between current
pulses conducted in the prim ary w inding of T1085 by
Q1080.
C l 136 and R1132 comprise a tim ing circu it to deter
mine the interval between the regulating pulses. C l 136
charges tow ard the voltage level at pin 6 of U1130 through
R1132 and CR1132. When the charge on C l 136 reaches a
level about 0.6 volt more positive than the voltage level at
the gate of Q1138, Q1138 conducts current to discharge
C l 136 and, at the same tim e, forw ard bias the base-emitter
junction of Q1150, When the current flo w through Q1138
falls below the level necessary to keep Q1138 on, Q1138
w ill turn o ff and C l 136 w ill start to charge again.
When Q1138 turns on, Q1150, which is quiescently
biased o ff, turns on and conducts a current pulse through
C ircuit Description—434
the prim ary w inding of T1150. T1150 couples a negative-
going pulse to the base o f Q1040 through CR1040. Q1040
turns on and its collector moves positive to tu rn on Q1Q50,
which starts the sequence o f events necessary to generate a
turn-on pulse fo r Q1080.
The time interval between pulses generated in the Regu
lator circu it is altered by m onitoring variations in the —15
volts supply. For example, when heavy load demands are
being made on the —15 vo lt supply it attempts to go posi
tive. This positive movement results in a positive movement
in the voltage level at pin 6 of U 1130. A more positive level
at pin 6 of U 1130 shortens the am ount of tim e required by
C l 136 to charge to the level at which Q 1138 turns on. This
results in more turn-on pulses being generated for Q1080,
thereby increasing the am ount of energy transferred
through T1085 per u n it o f time,
POWER SUPPLY SECONDARY
General
The Power Supply Secondary circuit rectifies the AC
voltages present in the secondary windings of Power Trans
form er T1085 to provide the necessary DC supply voltages
to the instrum ent circuitry. A schematic of this circuit is
shown on diagram 10 at the rear o f this manual.
Rectifier Circuits
A ll of the rectifier circuits in the Power Supply Second
ary are half-wave rectifiers. LI 102, LII04, and LI 106 provide
added filterin g for the +115 volt, +15 volt, and the —15
vo lt supplies respectively. T1100 provides common-mode
in d u cta n c e to suppress the 25-kilohertz interference
originating in the power supply circuit. The High-Voltage
supply is a series of ten half-wave rectifier power supplies.
Total ou tp u t voltage o f the supply is approxim ately 4.1
kilovolts fo r use in the CRT circuit. CR1199 provides DC
filam ent voltage to the CRT.
CRT CIRC UIT
General
The CRT Circuit contains the control circu itry necessary
fo r operation of the cathode-ray tube (CRT). Fig. 3-14
shows a detailed block diagram o f the CRT circuit. A
schematic of this circu it is shown on diagram 11 at the rear
of this manual.
Unblanking A m plifier
The Unblanking A m plifie r circu it controls the CRT
intensity level from several inputs. The effect of these input
signals is to either increase or decrease the trace intensity,
or to completely blank portions of the display. A portion
of integrated circuit U940A is used to convert the voltage
3-21
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