drop across res i st ive -d ivider network R 904 - R 906. The
feedback t h r o u g h this n etwo rk a n d R907 i s c o m p a red
to the reference level esta b l i s h ed at the base of 09 1 1 .
Any variation i n outp ut voltage of the s u pply (d u e to
r i p p l e , c h a n g e of c u r re nt t h ro u g h the load, etc . ), i s
i m mediately t ra n s m itted t h ro u g h error a m p l i f i e r 0907-
09 1 1 -09 1 4 to t h e base of 0900, changing its
con d u ct i o n a n d n u l l ify i n g the o r i g i n a l o utput va r i a t i o n .
Tr a n s i stor 0 8 9 5 protects t h e + 1 oo-vo lt s e r i e s reg u l a to r
( 0900) i f excess c u rrent i s dema nded f r o m t h i s s u p ply.
Essent i a l ly, a l l c u rrent from t h i s supply flows t h ro u g h
R 89 6 . Whe n excess c u r rent i s dema nded from t h e
+ 1 00-vo lt s e r i e s reg u l ator, d u e t o
a
s hort c i rc u it o r
s i m i la r m a l f u n ct io n a t t h e o utp ut o f t h i s s u pp ly, t h e
voltage drop a cross R 89 6 i ncreases, ca u s i ng 0895 to
i ncrease conduction. The resu lt i ng cu rrent t h ro ug h
0895 red u c e s
the conduction of
0900
to
l i m i t t h e
s u pply c u r r e nt t o a safe l evel .
C RT I NTE R CO N N E CTS
The ASTIG screwdriver adjustment, R841, which is
used in conjunction with the front-panel FOCUS
control
to provide a well-defined display, varies the
positive level on the astigmatism element of
t h e
crt.
Geometry adjustment R 943 varies the positive level on
t h e geometry e l e me nt
to control the overall geometry
of t h e
display. TRACE R OTATION adjustment R 94 9
control s t h e c u rr e nt
through L980 to provide
adjustment of the display alignment.
LOW-VO LTAG E POWE R S U P P LY
�
The Low-Voltage Power Supply provides the operating
power for the Monitor. Electronic regulation is used to
provide stable, low-ripple output voltages. A schematic
diagram of the Low-Voltage Power Supply is shown
on diagram 6 at the rear of this manual. A detailed
block diagram, showing each m ajor stage of this
circuit, is superimposed on the schematic with wide
shaded lines. The stage names (given as sub-headings
in the following discussion) can be found in the
shaded blocks on diagram 6.
POWE R I N PUT
Power is applied to the primary of transformer T950
through
fuse F950, thermal cutout S960, ON/OFF
switch
S950, and Line-Voltage Selector plug P951 or
P952. The Line-Voltage Selector plugs allow changing
the primary winding taps of T950 to meet different
line-voltage and regulating range requirements. Line
fuse F950 should be changed for each nominal line
voltage (current rating of fuse for 220-volt operation
must be 0.4 A slow-blowing type; for 1 20-volt
operation the current rating of the fuse must be 0. 8 A
slow-blowing type).
Thermal cutout S960 provides thermal protection for
this instrument. If the internal temperature of the
REV A, JAN 1 981
Theo ry of O peration-608
i nstr u me nt exceeds a safe operati ng level, 5960 opens
to i nterru pt the appl ied power. When t h e temperat u re
retu rns to a safe leve l , S 960 a uto matica l ly closes to
re-apply t he power.
R E CTI F I E R AN D F I LT E R
A f u l l-wave br i dg e c i rc u it, co m posed o f
CR951-CR952-
CR953-CR954
rect ifies t h e ac voltage from t h e
s econdary o f T950. F i lt er i ng i s p rovided
by
C 9 5 1 a nd
C952.
+ 1 8-VO LT U N R EG U LATE D S U P P LY
T h e + 1 8-Volt U n reg u l at ed S u pply p rovides u n reg u lated
power for the h i g h-voltage tra nsformer (T850) on
diagram
5. Fuse F951 provides circuit
protect ion in the
event of an overload.
+ 1 5 -VO LT R E G U LATE D S U P PLY
The +15-Volt Regulated Supply, in addition to providing
power to circuitry throughout the instrument, provides
a reference-voltage source to establish the
operating
level for t h e feedbac k
regulator of the -15-Volt
Regulated Supply. The regulator for the +15-Volt
R egulated Supply is a feedback amplifier system that
operates between ground and the +18-Volt
Unregulated Supply. Current to the load is delivered by
series-pass transistor 0955, which is located in
t h e
output side of the supply. The supply voltage is
established by the drop across resistive-divider
network R 959-R 958- R957. The feedback trhough this
network is compared to the reference level established
at the base of 0965 by the voltage drop across
VR968. Any variation in output voltage of the
supply
(due to ripple, change of current through the load,
etc.), is immediately transmitted to the base of 0955
and nullified by a change in 0955 conduction,
maintaining a steady output.
The output of the supply is set to exactly +15 volts by
adjustment of R958, the +15-V Adjust.
Transistor 0970 protects the +15-volt series regulator
(0955) if excess current is demanded from this supply.
Essentially, all current from this supply flows through
R 954. When excess current is demanded from the
+15-volt series regulator, due to a short circuit or
similar malfunction at the output of this supply, the
voltage drop across R 954 increases enough to turn on
0970. The resulting current through 0970
reduces t h e
conduction of 0955 to limit the supply current to a
safe level.
Fuse F 9 5 3
provides circuit protection i
n the
event of an overload or regulator malfunction.
- 1 5 -VO LT R EG U LATE D S U P P LY
The regulator for the -15-Volt Regulated Supply
consists of series-pass transistor 0976 and error
amplifier 0987-0944-0981 . This is a feedback
4-9
