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used
in
conjunction
with
the
normal
voltage
read-
I
ings
shown
on
the
schematic
and
the
additional
I
procedures
given in
the
following
paragraphs
I
should
suffice
t o
isolate
a
fault
to
a
component
or
I
small
gnoup
of components.
The
normal
voltages
I
shown
on
the
schematic
are
positioned
adjacent
I
t o
the
applicable
t e s t
points
(identified
by
encir-
I
cled
numbers
on
the
schematic
diagram.
5-36 A list that includes the symptoms and prob-
able c a h s e s of many possible troubles
is
included.
I
If either: high or low output voltage
is
a symptom,
I
there are two methods of isolating the fault.
The
I
first i s a simplified procedure that involves only
I
measuri'ng voltages; the second i s a more thorough
approach requiring that transistor s t a g e s be open-
I
ed or shorted.
Both methods are described a s fol-
lows:
No outbut in a l l
I
voltage ranges
I
I
Low
output
or
I
no
outqut
only
i n
0-3O10V
ranges
. I
I
High
ohtput
I
Probable Cause
a.
CR28 shorted
b.
CRlO open
Refer to Table 5-2, then
Table 5-3
Refer t o Table 5-2, then
Table 5-4
~mpropkr
current
a.
R22,
R24,
R23
incorrect
I
limit
value
value
I
High
~ i ~ p l e
a.
Check operating setup
for ground loops
b.
If output floating, con-
nect 1 pf capacitor between
output and ground
c.
Check for excessive in-
ternal ripple; refer to Table
5-2
Symptom
(Continued)
Poor line regu-
lation
Poor load regu-
lation
Oscillates
Poor stability
Poor transient
recovery
Probable Cause
(Continued)
d.
Ensure that supply i s not
current limiting under loaded
conditions
e.
Check for low voltage
across C6-C9 or C15
f .
CR27 inoperative
a.
Refer to Table 5-2
a.
Improper measuring tech-
nique; refer to paragraph 5-3
b.
Refer to Table 5-2
c.
Ensure that supply i s not
current limiting under loaded
conditions
a.
Noisy programming resis-
tor R21
b.
Check VR2, CR19, CR20,
Q5, Q6,VR1, CR27, and
CR2 9
a.
Check R18 and C3
1.
First,
the reference,
bias,
and filtered
DC
voltages
a s
given
in
Table
5-2
should
be
checked.
Then
the
voltage
levels
a t
critical
points
(base
and
collector)
i n
the
feedback
loop
should
be
measured
and
compared
to
the
normal
voltages
given
on
the
overall
schematic diagram
a t
the
rear
of
the
manual.
This
method
of
trouble-
shooting
a feedback
loop
i s
not
always
conclusive;
a
better
method
i s
described
in
(2).
2.
First,
measure
the
reference, b i a s ,
and
filtered
DC
voltages
a s given in
Table
5-2.
Then,
drive each
stage
in
the
feedback
loop,
into
con-
duction
or cutoff
by
either
shorting
or
opening
the
previous stage
a s
indicated
in
Tables
5-3
or
5-4.
Table 5-2.
Reference, Bias, and Filtered DC Voltage Troubleshooting
Meter
Meter
Normal
Normal
Probable Cause
Common
-
Positive
V d c
Ripple (P-P)
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