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voltage
should
be
within
6.3
+or-
0.6
volts
for
the
power
supply
to
regulate
properly.
Floating Power Supply
The
floating
power
supply
is
identical
in
operation
to the collector
power
supply.
Con-
sequently,
the
same
types
of
troubles
will
occur
and
the
same
general
troubleshooting
techniques
may
be employed.
Since the float-
ing
power
supply
is ungrounded
and is riding
on the output voltage of the bias power supply,
it is doubly important that all voltage measure-
ments
be
made
with
respect
to
some
fixed
point
in
the
circuit
rather
than
with
respect
to ground.
If voltage measurements
are made
with
respect
to the emitter
voltage of Q6854,
readings
obtained
will be the same regardless
of the position
of the PULSE
VOLTS
Polarity
switch
or
the
setting
of
the
BIAS
VOLTS
controls.
Bias Power Supply
The
bias
power
supply
is
somewhat
dif-
ferent
in
operation
from
either the collector
power
supply
or the floating power
supply
in
that
two
sets
of
rectifiers
and
two
series
regulators
are
used
to
allow
the
voltage
to
vary
continuously
between
+5
and
-5
volts.
Troubles
occuring
in
the
bias
power
supply,
however, do correspond to troubles whichoccur
in the other
power
supplies.
Troubles usually
consist
of
a
lack
of regulation,
unvariable
output
voltage,
improper
output voltage limits,
or
excessive
ripple voltage.
Checks
made
on
the
supply
to
determine
the
cause
of
these
troubles
should
be
made
with
a
load on the
output.
In the bias power supply, a lack of regulation
generally
occurs
simultaneously
with
an un-
variable
output
voltage.
This
is because
the
same circuitry is involved in maintaining regula-
tion
as
is
involved
in
adjusting
the
output
voltage.
Both
troubles
are
usually
due
to a
failure of one of the transistor stages.
In adjusting
the output
voltages
or in main-
taining
regulation,
Q6884
acts
as the sensing
stage
for
the
power
supply.
That
is, Q6884
detects
the
difference
(error
signal) between
the desired
output voltage
and the actual out-
put
voltage.
The
error
signal is then
applied
to
the
series
regulators
to adjust the output
of the power
supply
to the correct
level.
The
conduction
of
Q6884
is
controlled
by
both
the
setting of
the
BIAS
VOLTS
controls
and
by
the
output
voltage
of
the
power
supply.
Transistor
Q6884
controls
the
operation
of
the
other
transistors
in
the
circuit.
If the
power
supply
is not
regulating,
it is because
one
of
the
stages
is not responding
properly
to
the
error
signals.
The
defective
stage
could be any one of those located in the power
supply.
From
the
conditions
of
the
output
voltage,
it
is possible
to predict
how
each
stage
should
react
to
the
error.
When
this
has
been
established,
you
should
then check
the
operation
of
each
stage,
starting,
with
Q6884.
The
conduction
of
each stage can be
determined by measuring the emitter to collector
voltage
of
each
transistor.
When a
stage is
checked
where
the
transistor
is
conducting
heavily
when
it should be cut off or is cut off
when
it
should
be
conducting
heavily,
this
will serve to isolate the defective stage.
The
voltage
limits
for
the
power
supply
are
determined
by
the
resistors
in the base
circuit of Q6884.
If the power supply seems to
be
operating
normally
except
that the output
voltage limits have shifted slightly , the resistors
in the base circuit of Q6884 should be checked
first.
It
is
possible
for
you
to
reduce
the
number of resistors you must check by observing
operation
of
the
power
supply
with the BIAS
VOLTS
red
knob
in
both
the
Xl
and
X10
positions.
Excessive
ripple voltage
at the output of the
bias
power
supply
is usually
due to defective
filter
capacitors.
If
all
the filter capacitors
appear
to be in good
condition, the secondary
voltage
of
T6830
should
be
checked
against
the
figure
given
on
the
schematic
diagram.
Pulse Generator
A
trouble
occuring
in
the
pulse generator
section
of
the
Type
R
Unit
will
affect
the
pulse
applied
to
the
transistor
being tested.
If the trouble occurs in only one of the positions
of
the
PULSE
VOLTS
or
SERIES
RESISTOR
switches,
the
trouble
is probably
a defective
resistor or switch,
In such a case the resistors
used
in
the
position
of the switch
where
the
trouble occurs should be checked.
Note
The mercury
switch, SW5803, will
not
operate
properly
unless
the
Type R Unit is in the upright position.
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