Circuit Description—Type 324
of collector current increases the current through the load,
keeping the —5 V supply within design limits.
+11 V and +8.5 V Power Supplies
One side of the N6 secondary winding is referenced to
the +5 V Power Supply line. Positive pulses from the upper
side of the winding add to the 5 V reference and are applied
through D549 and R549 to generate the +11 V power
supply. The N6 winding also supplies current through D545
and R547 to develop the +8.6 V reference across D547.
This is filtered by L551, providing an 8.5 V decoupled
output.
Since the +8.6 V is not present during turn-on, current
from the Power Pack flows through R550, R572 and D551
to provide starting power to the oscillator control circuit.
D550 limits this starting voltage to +7.2 V at the
R550-R572 junction. A fter the oscillator has started, the
voltage across D547 increases to its prescribed +8.6 V , and
D551 becomes back-biased, isolating the +8.6 V reference
from the Power Pack input voltage.
High Voltage Power Supply
The N5 secondary winding drives the High Voltage
Multiplier which consists of D575 and C573-C579. The
multiplier has three negative high-voltage taps: one at
—1900 V to supply the CRT cathode; one at —2250 V
supplying the IN T E N S IT Y control circuit; and one at
—1200 V for the FOCUS circuit. The —1900 V tap is con
nected into the CRT directly-heated cathode circuit in a
manner that keeps the AC filament voltage from changing
the cathode potential with respect to the grid, thus elimin
ating CRT intensity changes. The IN T E N S IT Y L IM IT con
trol, R538, is an internal adjustment which sets the mini
mum voltage difference which can exist between the con
trol grid and cathode. This avoids cathode damage caused
by excessive cathode current.
The least negative voltage taken from the High Voltage
Power Supply appears at CRT pin 13, the focus anode. The
setting of the FOCUS potentiometer, R581, in combination
with ASTIG potentiometer R597, determines the sharpness
of the trace presentation. Only the FOCUS control is used
during routine operation, and it is capable of focusing the
trace at any intensity setting once the ASTIG control has
been properly set.
CRT Circuit
+ 100 V appears at pin 5 whenever the oscillocope is
energized. Pin 9 has 0 V applied except during sweep time
or external horizontal operation, during which time +100 V
is applied. When the voltages at pins 5 and 9 are unbal
anced, the CRT beam is deflected into the pin 9 plate and
cannot strike the CRT phosphor. When +100 V is applied
to both plates, the deflection effect is nulled, and position
control is exercised by the horizontal and vertical deflec
tion plates.
T h e G EO M ETR Y control adjusts for a minimum
amount of bowing of vertical and horizontal lines, regard
less of the area to which they are positioned.
The TR ACE R O TA TIO N potentiometer (R592) con
trols the current through the trace rotation coil, thus
creating a magnetic field through which the CRT electron
beam passes. When TR ACE R O TA TIO N is properly ad
justed, horizontal sweep voltages will cause the trace to
follow the paths which are parallel to the horizontal grati
cule lines.
Explanations regarding the remaining CRT elements
appear in conjunction with the High Voltage Power Supply
description.
Low Battery Sensing Circuit
The Low Battery Sensing Circuit employs a relaxation
oscillator (R 506, C507 and DS509) operating at a fre
quency of approximately 1 Hz. When the input power
exceeds 6.5 V , Q571 is saturated and the voltage at its
collector is not sufficient to fire the neon LOW B A TT indi
cator, DS509. When the input falls below 6.5 V , Q571
turns off and C507 charges toward +100 V until DS509
fires and partially discharges C507. The cycle then repeats.
Although DS509 will blink in any power mode when the
supply is less than 6.5 V , it is of primary concern during
internal battery operation. If the oscilloscope is left ener
gized in the internal battery mode for a considerable period
of time after the battery output falls below 6.5 V, the cells
may be damaged to the point where they can no longer be
charged.
POWER PACK<$)>
General
The Power Pack contains the battery which supplies the
internal power, connectors for applying external AC or DC
power, a transformer and rectifiers for AC operation, and a
battery charging circuit for recharging the internal battery
from an external AC source. The switching circuitry which
selects the power source is also contained in the Power
Pack.
Block Diagram Description
Refer to the block diagram contained on the Power Pack
schematic diagram page.
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