Wavetek 142 Instruction Manual page 27

Table 4-2.
TROUBLE-SHOOTING GUIDE
(continued)
Symptom
Corrective
Action
VCG
Amplifier
&
IC3-IC6
.
a)
Voltage
at
emitter of
Q21
should
move from 0
to
—5
volts.
(Continued)
b)
Source
of
Q22
remains
at
0 and
drain
moves from +15
V
to+IOV.
c)
Source of
Q23
moves from
0
to
—5 V
and
drain
moves from
-15 V
to
-10
V.
d)
Source of
Q24
moves from +15
V
to
+10
V,
e)
Source
of
Q25
moves
from
—15 V
to
—10
V.
f)
Voltage
at
drain of
Q27
follows voltage at gate of
Q26.
g)
Voltage
at
drain of
Q29
follows voltage
at gate of
Q28.
Triangle Amplifier Check-
Short
the gate of
Q1
to
ground and check
the following:
a)
Gate
of
Q2
is
at
0
volts.
b)
Voltage
across
C14
is
approximately
6.6
volts.
c)
If
"a" or
"b"
is
not
true,
check
all
transistors
in
Triangle
Amplifier
for possible trouble.
Hysteresis Switch
Check
a)
Voltage
at collector of
Q9
is
approximately
6.6 volts.
b) Voltage
at collector
of
Q14
is
approximately
7
volts.
c)
Voltage
at junction of
R49
and
R50
is
approximately
—3
volts.
d)
For normal
operation, voltage
at
the emitters of
Q1
1
and
Q16
switches between +2.5
volts
and —2.5
volts.
If
switch
does not
oscillate,
proceed
as follows:
e) If
voltage
at
gate of
Q2
is
greater than
+1.25
V,
the voltage
at the emitter of
Q16
should be +2.5
V
and the emitter of
Q1
1
should be
—2.5
V.
If
the voltage
at
the gate of
Q2
is
less
than
—1.25
V, the
voltage at the emitter of
Q16
should
be
—2.5
V
and the emitter of Q1
1
should be +2.5
V
or the
Hysteresis Switch
is
malfunctioning.
f)
Q10
should be
saturated
if
voltage
at
pin
1
of IC1
is
above
ground, and
Q15
should be
saturated
if
voltage
at pin
4
of
IC1
is
below ground.
g)
If
Hysteresis
Switch
appears to function normally, and
Triangle Amplifier
also appears to function normally, but
no
oscillations are present
at
the output; check
CR7
through
CR10,
Q24
and Q25.
Sine Amplifier Check
If
the voltage at
the bases of
Q30
and
Q31
are
not
equal,
check
Q30
through
Q35
for possible trouble.
Output
Amplifier
Check Check
the
collector
and
emitter voltages of
all
transistors in
the
Output
Amplifier
circuit.
Some
key
voltage
test
points are
listed
below:
a)
Voltage
at
junction of
C94
and C93
is
zero
volt.
b)
Voltage
at
base of
Q52
is
approximately
+19
volts.
c)
Voltage
at base of
Q53
is
approximately
—19
volts.
d)
Voltage
at
pin 12
of
ICS
is
between
-5
volts to
+10
volts.
4-6
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