Circuit
Description
—
7623/R
7623
Service
LOW-VOLTAGE
POWER
SUPPLY
The
Low-Voltage
Power Supply circuit provides the
operating power for this
instrument from
six
regulated
supplies.
Electronic regulation is
used to provide
stable,
low-ripple
output
voltages. Each supply (except the -i 130
V
supply,
which
is fused)
contains a short-protection circuit
to prevent
instrument damage
if a supply is inadvertently
over-loaded
or shorted
to
ground.
Fig. 3-22 shows a
detailed
block diagram
of the Low-Voltage Power Supply
circuit.
A schematic of this circuit
is shown on diagram 8
at
the rear of this
manual.
Power
Input
Power is applied
to
the
primary of transformer T801
through
line fuse F1000, thermal cutout S1000, and
POWER
switch
S1001. The Voltage-Selector Jumper,
P1001,
connects
the
two halves
of the primary of T801 in
parallel
for 110-volt (nominal) operation. Voltage-Selector
Jumper P1002
connects the two halves of the
primary in
series for
220-volt
(nominal) operation. The line
fuse,
F1000,
must
be changed to provide the correct protection
for
220-volt nominal
operation.
Each
half of the
primary of T801 has taps above and
below the
110-volt (220-volt)
nominal
point. When
the
Voltage
Selector Jumper is moved
from LOW to MED to
HI,
more turns are effectively
added to the primary winding
and
the turns ratio
is
decreased to compensate for the
increased
primary
voltage. This configuration
extends the
regulating
range
of
the
7623.
For
the
R7623,
a fan
provides forced-air cooling. The
fan is
connected in
parallel with one half of the primary
winding
of T801.
Therefore, it always has the same voltage
applied
regardless of the position
of the Voltage-Selector
Jumper.
Thermal
cutout S1000 provides thermal protection for
this
instrument.
If
the internal temperature of the instru
ment exceeds a
safe operating level, S1000 opens to
interrupt the applied power. When
the temperature returns
to a safe
level, S1000
automatically closes to re-apply the
power.
-50-Volt
Supply
The following
discussion includes the description of the
50
V Rectifier, 50 V Series Regulator, -50 V Feedback
Amplifier,
- 50
V Reference, and -50 V Current Limiting
stages. Since these stages are closely related in the operation
of
the -50-volt regulated output, their performance is most
easily
understood when discussed
as a unit.
The
50 V Rectifier assembly CR808 rectifies the output
at
the
secondary of
T801 to provide the unregulated
voltage
source for both
the —50- and +50-volt supplies.
CR808
is connected as a bridge rectifier and its output
is
filtered
by C808-C809.
Transistors Q886, Q896, Q900
operate
as a feedback-stabilized
regulator
circuit to main
tain
a constant -50 volt output level. Q886 is connected as
a
differential
amplifier
to
compare
the feedback voltage at
the base of
Q886B against the reference voltage at the base
of
Q886A. The
error output at the collector of Q886B
reflects the difference, if
any, between these two inputs.
The
change
in
error-output level at the collector of Q886B
is
always opposite in direction to the change in the
feedback
input at the base of Q886B (out of phase).
Zener diode VR890 sets a reference
level of about —9
volts
at the base of Q886A. A feedback sample of the
output voltage
from
this supply
is connected to the base of
Q886B
through
divider R880-R881-R882. R881 in
this
divider
is adjustable
to set the output level of this supply.
Notice that the
feedback voltage to this divider is obtained
from
a line
labeled -50 V Sense. Fig. 3-23 illustrates the
reason
for
this
configuration. The inherent resistance of the
interconnecting wire
between
the output of
the
-50-Volt
Supply
and the load produces a voltage drop which is equal
to
the output current multiplied by the resistance of
the
interconnecting
wire. Even
though the resistance of the
wire is small, it
results in a substantial voltage drop due to
the
high output
current of this supply. Therefore, if the
feedback
voltage were obtained
ahead of this drop, the
voltage
at the load
might not maintain close regulation.
However,
the
-50
V Sense feedback configuration over
comes this problem
since it obtains the
feedback voltage
from
a
point as close as practical to the load. Since the
current
in the —50 V Sense line is small and constant,
the
feedback voltage
is an
accurate sample of the voltage
applied
to the load.
Regulation
occurs
as follows: If the output level of this
supply
decreases (less
negative) due to an increase
in load,
or
a decrease in input voltage
(as a result of line voltage
changes or
ripple),
the voltage across divider R880-
R881-R882
decreases also. This results
in a
more positive
feedback
level
at
the
base of Q886B than that established
by
the
—50 V Reference stage at the base of Q886A. Since
the transistor
with the more positive base controls the
conduction of the differential amplifier, the output current
at
the
collector of Q886B increases. This increase in output
from
Q886B allows more current to
flow through Q896
and Q900
to result in increased conduction of - 50 V
Series
Regulator Q903.
The load
current increases and the output
voltage of
this supply also increases (more negative). As a
result,
the feedback voltage from the —50 V
Sense line
increases and
the base of Q8868
returns to the same level as
the
base of
Q886A. Similarly, if the output level of this
supply increases
(more
negative), the output current
of
Q886B
decreases. The
feedback through Q896 and Q900
reduces
the
conduction
of the -50
V Series Regulator to
decrease the
output voltage of this supply.
3-27
Summary of Contents for 7623
Page 1: ...MANUAL 7623 R7623 STORAGE OSCILLOSCOPE SERVICE MANUFACTURERS OF CATHODE RAY OSCILLOSCOPES ...
Page 51: ...Fig 3 2 Block diagram of Logic circuit Circuit Description 7623 R 7623 Service ...
Page 72: ...W NJ 00 Fifl 3 22 Low Voltage Power Supply detailed block diagram ...
Page 73: ...Circuit Description 7623 R 7623 Service ...
Page 74: ...CO NJ CD Fig 3 22 Low Voltage Power Supply detailed block diagram cont ...
Page 75: ...Circuit Description 7623 R 7623 Service ...
Page 97: ...Circuit Description 7623 R7623 Service 3 51 ...
Page 98: ...Circuit Description 7623 R7623 Service Fig 3 39 Output Pulses for the Storage Circuits 3 52 ...
Page 103: ...Circuit Description 7623 R7623 Service 3 57 ...
Page 108: ... Ç À Fig 4 2 Location of circuit boards in the 7623 ...
Page 109: ...Fig 4 3 Location of circuit boards in the R7623 Maintenance 7623 R 7623 Service ...
Page 113: ...Maintenance 7623 R7623 Service Fig 4 6 Circuit Isolation Troubleshooting Chart 4 9 ...
Page 165: ...7623 BLOCK DIAGRAM ...
Page 166: ...7623 R7623 Service Front of Board ...
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Page 173: ...7623 Logic ...
Page 175: ...Vertical Interface A4 ...
Page 178: ...Vertical Interface ...
Page 180: ...Vertical Amp A5 ...
Page 184: ...Horizontal Amp A6 ...
Page 186: ...7623 TO P450 VERT AMP 3 HORIZONTAL AMPLIFIER ...
Page 188: ...Output Signals A7 ...
Page 190: ...FROM 7G23 Output Signals g ...
Page 195: ...FROM LV POWER SUPPLY 7623 CRT CIRCUIT ...
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Page 202: ...Storage Output A14 ...
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Page 205: ...7623 R7623 Service Fig 6 14 A15 Cal Storage circuit board ...
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Page 209: ...7623 R7623 Service Fig 6 15 A16 Readout System circuit board ...
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