Circuit Description— Type M
The signal at the anode of D6352 is a single regenerated
negative-going pulse that occurs each time the sync trigger
from the oscilloscope is applied to the Q6350 base circuit.
This regenerating of the sync triggers standardizes the vary
ing size and shape of the sync triggers originating from the
various types of oscilloscopes. The regenerated trigger be
comes a sharp negative-going spike when coupled through
C6352 and is easily handled without jitter by the Ring
Counter.
(3)
Free-running operation.
The switching B.O. free
runs when two or more channels are on and the ALTER-
NATE/CHOPPED switch is set to CHOPPED. When the switch
is in this position, one side of the switch disconnects pin 8
of the interconnecting plug from ground disabling the oscil
loscope sync amplifier and connects one side of R6364 to
ground.
The other side of the ALTERNATE/CHOPPED switch con
nects +100 volts to a voltage divider consisting of R6362
and R6364. This voltage divider makes 35 volts available for
the collector of Q6364.
The 35 volts at the collector of Q6364 causes D6362 to
be reverse biased. With D6362 reverse biased, Q6364 is
just into cutoff. Since both Q6350 and Q6364 are now in
cutoff, the voltage divider of R6353 and R6356 starts charg
ing C6355, C6356 and C6352. The charging of these three
capacitors continues until the anode of D6352 is elevated
positive enough to cause D6352 and Q6350 to conduct.
When Q6350 starts to conduct, current through T6350 in
duces a negative-going voltage which is applied to the
base of Q6350.
This negative-going voltage causes Q6350 to conduct more
and more heavily until Q6350 is in saturation. When
Q6350 is saturated the change in current through T6350
ceases. Since the base of Q6350 no longer has a negative
going voltage applied to it, it starts positive toward the 13.6
volt supply voltage.
The anode of D6352 has a large amount of capacitance
tied to it which must change its charge if the anode is to
change potential. The anode of D6352 is therefore very slow
in changing its potential. The cathode goes positive more
rapidly than the anode and reverse biases D6352. The
anode of D6352 starts charging positive at a rate deter
mined by R6353 and R6356, charging C6355, C6356 and
C6352. When the three capacitors and the anode of D6352
are positive enough for D6352 and Q6350 to again conduct,
the cycle repeats.
When the base of Q6350 starts positive toward the 13.6
supply voltage after saturation, it overshoots the 13.6 supply
voltage because of the collapsing field of T6350. This posi
tive overshoot is caught by the base-emitter junction of
Q6364, turning it on. The collector of Q6364 now goes
negative, producing a negative pulse which is capacitively
coupled to the Blanking Amplifier in the oscilloscope. Since
this pulse occurs delayed from the actual time of switching,
it blanks the CRT at the same time as the switching transient
reaches the deflection plates after being delayed in the
vertical amplifier of the oscilloscope.
SN 101-824
(1 ) Single-trace operation.
Assume all channels are
on and that channels B, C, and D are about to be turned
off. When the MODE switch for channel B is set to OFF,
approximately 0.5 ma matrix current flows through R6320.
When channel C and D MODE switches are set to OFF,
total current flowing from R6320, R6330 and R6340 is about
1.4 ma. The total current is enough to starve the current
path through D6360. Diode D6360 reverse biases and un
clamps the junction where it is tied to R6360. Resistor R6360
is “ long-tailed” to the +225-volt supply so that the current
through it remains the same regardless of the operating
mode.
When D6360 reverse biases, the voltage at the junction
of D6360 and R6360 drops from about 12.9 volts to about
12.2 volts. The voltage decrease causes diode D6352 to
conduct. The drop across D6352 and that across the base-
emitter junction of Q6364 essentially cancel. Q6364 emitter
current flowing through R6354 sets the emitter level for
Q6350. Under these conditions, Q6350 is cutoff and will
not operate, regardless of the setting of the ALTERNATE/
CHOPPED switch. Thus, chopping-rate switching transients,
which might interfere with the usefulness of single-trace
displays, cannot occur, and triggers are not generated.
(2 ) Multi-trace
triggered
operation.
When
the
ALTERNATE/CHOPPED switch is set to ALTERNATE, one
side of the switch connects pin 8 of the interconnecting
plug to ground, which grounds R6368 and the cathode of
the oscilloscope sync amplifier. The sync amplifier dif
ferentiates and amplifies the positive-going sync trigger
generated by the oscilloscope sweep-gating multivibrator at
the end of each sweep cycle. The negative-going sync
trigger produced at the plate of the sync amplifier is ap
plied through pin 16 of the interconnecting plug to the
junction of R6367 and C6364, located in the collector circuit
of Q6364.
The other side of the ALTERNATE/CHOPPED switch dis
connects divider resistors R6365 and R6366 from the emitter
circuit of Q6350. The divider is now connected to the
switch end of R6367 to supply an operating potential for
the oscilloscope sync amplifier. Since the divider is discon
nected from the emitter circuit of Q6350, current through
R6355, R6353, R6354 and Q6364 determines the emitter
level of Q6350.
When more than one channel is turned on, matrix currents
to R6360 decrease. Diode D6360 becomes forward biased
and supplies the current path to R6360. The voltage at the
junction of D6360 and R6360 rises from about +12.2 volts to
about +12.9 volts and reverse biases D6352. The clamping
action of Q6364 holds Q6350 cutoff.
The sync trigger, applied to the R6367/C6364 junction,
is coupled through C6364, R6364 and C6351 to the col
lector circuit of Q6350. The sync trigger is not applied
to the collector of Q6364, however, because D6364 is re
verse biased. To provide a load and a complete circuit
for Q6364 during alternate operation, the collector of Q6364
ties to R6368 by forward biasing D6368. The switch end
of R6368 connects to ground through the ALTERNATE/
CHOPPED switch.
With the negative-going sync trigger applied to the
collector circuit of Q6350, current flows through T6350
primary and into C6350. The varying magnetic flux in the
primary induces a negative-going voltage at the base of
Q6350 and starts the blocking oscillator action. This action
continues until Q6350 is driven into saturation and collector
current ceases to increase. Toroid T6350 field collapses
3-5
