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Model 181A/AR
. 4-31. The internal sweep from the Horizontal Plug-
In is coupled through the HORIZONTAL
DISPLAY
switch to the horizontal output amplifier.
Here it is
^
converted to a differential signal,
amplified,
and ap-
plied to the CRT horizontal deflection plates.
4-32.
EXTERNAL.
4-33. Positioning the HORIZONTAL DISPLAY switch
_to EXT
removes the internal display voltage from the
Horizontal Plug-In.
The unblanking gate and the in-
ternal sweep are therefore not generated by the plug- in.
4-34. Gate amplifier operation (and thus CRT intens-
ification) is determined by: an externally applied Z-
' Axis Input
signal, the chopped
blanking signal from
the Vertical
Plug-In, and an unblanking signal from
the storage pulsecircuit.
Whenin EXT, the gate amp- .
lifier will produce an alternate trigger only if the ex-
-
ternal input signal is similar to the normal unblanking
gate.
4-35. The externally applied horizontal deflection sig-
nal is preamplified,
coupled to the output amplifier,
converted
to a differential output,
and applied to the
CRT horizontal deflection plates.
4-36. CIRCUIT DESCRIPTION.
4-31. The following paragraphs area detailed descrip-
tion of the circuits andtheir functions in the Model 181
A/AR Oscilloscope.
4-38. LOW
VOLTAGE
POWER
SUPPLY (LVPS).
4-39, The low voltage power supply produces six dc
voltages plus the CRT
write and flood gun filament
power.
The -100, -12.6,
+15, +100, and +156 volt
supplies are regulated and used throughout the Model
181A/AR and the plug-in units.
An unregulated 423v
is produced for use by the High Voltage Power Supply
(HVPS) and the pilot lamp.
A regulated «105v is also
produced for use only within the LVPS.
4-40, Figure
4-6 illustrates a basic regulated power
supply.
The series regulator and the parallel combi-
nation of the loadandthe
sensing device divide the en-
tireapplied voltage.
Ifthe loadchanges, thus changing
the voltage
drop across the load, the sensing device
will detect
it and cause the resistance of the series
regulator to change in the required manner to restore
the output to the desired voltage level.
4-41. Refer
to the schematic
diagram
of the LVPS,
`
Figure 8-21.
Theclosing of S5 supplies power to the
primary of Ti.
The dual primary windings of T1 may
be connected in series for 230v operation
or in para-
llel for 115v operation.
$6, located on the rear panel
of the instrument, switches these windings for 115v or
230v operation.
4-42. The ac voltages developed by the secondary wind-
ings of T1
are
bridge rectified,
filtered, fused and
applied to the regulatingcircuits.
Decoupling RC and
LC filter networks are employed for circuit isolation
where required.
02612-2
Section IV
Paragraphs 4-31 to 4-48
4-43. The -100v output is used as a reference for the
other regulating circuits.
It must be adjusted first
since its output will affect all other regulated LVPS
outputs.
4-44, -100 VOLT SUPPLY.
A portion of the de volt-
. age from the -100v rectifier-filter circuit is dropped
across ATR5 and series regulator Q4.
The remainder
is dropped across the voltage divider network A8R35, |
A8R36,
and A8R37.
If the -100v supply were to de-
crease
in amplitude,
a small portion of the positive-
going change would be felt on the base of A8Q12.
This
change
would be coupled through A8V2 and A8Q11 to
the emitter of A8Q12.
The differencebetween
the in-
puts to A8Q12,
a positive-going signal,
is coupled
throughcurrentamplifier, A8Q10, tothe base of series
regulator,
Q4.
Less
voltage
is dropped by Q4, and
the -100v supply increasestonormal.
A8C8 and A8R29
prevent high frequency oscillation of the series regu-
lator.
ABCR8 and A8CRO9 protect A8Q11 and A8Q12
respectively from reverse voltage breakdown in case
the output voltage is shorted.
AS8CRÍiO acis to prevent .
reverse charging of A8C10
in the event F6 opens.
A8CR12 protects A8Q10 and A8Q4 from reverse volt-
age breakdown during instrument turn- on.
4-48. +100 VOLT SUPPLY.
Operation
of the «100v
supply is similar to the - 100v supply except that the
base of A8Q2 is held at a constant voltage by A8V1.
' Any variations in the output are felt only on the base
of A8Q3 and inverted prior to coupling throteh A8Q1
to the series regulator Q1.
4-46. +105 VOLT SUPPLY.
Afiltereddc voltage from
A'"CRi-4andA7Ciis applied across A7R2, A8RÍ and
breakdown diode A8VR1.
Zener action keeps the top
of A8VR1 five volts more
positive than the bottom,
which is at +100v.
The +105v from A8VR1 is used to
-
provide bias current for A8Q1 and A8Q3.
4-41. 4156 VOLT SUPPLY. The rectifiedandfiltered
voltage from A7CRi-4
and A7C1
is applied across
.
ATRiand breakdown diode A7VR1.
Zener actionkeeps
the top of A7VR156. 2 volts more positive than the bot-
tom,
which is at «100v.
The 156 volt potential at
ATVRi
is applied to the CRT collector mesh,
and is
also used for the ERASE function.
4-48. -12. 6 VOLT SUPPLY.
The voltage from the
-12.6v rectifier filter is dropped across the series
regulator Q3, A8R22, and the load.
Any variation in
output is coupled through voltage amplifier A8Q9 and
current amplifier A8Q7 to the base of the series regu-
lator Q3.
| A8C6 and A8R20 prevent high frequency
oscillation of the regulator.
SERIES
REGULATOR
SENSING
mE
ammo
©
t o » G
DEVICE
m
One OA/AR- A-6
Figure 4-6.
Basic Regulated Power Supply.
4-5
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