Fluke 415B Instruction Manual page 51

415B
4-45. Assembly
Troubleshooting
4-46. 125
VOLT REGULATOR.
If
the
125
volt supply
fails to
regulate or
the
value
of
the output voltage
is
incorrect, proceed as
follows:
a.
With
a
VTVM
measure
the unregulated
output
of
the auxiliary supply: junction
of
R3
and R4
on the
Series Pass
P/C Assembly.
At
a
line voltage of
115
volts, the
dc
output should be 170
to
210
volts.
b.
Connect
a differential
voltmeter between
the cathode
of
CR2
on
the
Amplifier
P/C Assembly
and chassis
ground. Measure the output
of
the voltage
reference
tube, VI, Voltage should
be between
83. 3
and
85. 05
volts and should remain
constant
over a
line
voltage
range
of
103
to
127
volts.
c.
With
a
differential
voltmeter,
measure
the voltage
across zener diode
CR1
on the Amplifier
P/C As-
sembly.
Voltage should be
10. 8 to
13. 2 volts dc.
d. In a
properly operating 125
volt
regulator,
the
bases
of
Q4
and
Q5
should be
at
the
same
voltage
(83 volt
reference).
If
the
bases are
at
the
same
voltage but the supply will not regulate,
CR2
or
CR3
could possibly be
shorted. Eliminate
this
possibility
with
an ohmmeter
check.
If
the
supply
will not regulate
and
CR2
and
CR3
are
not
shorted,
0. 6
volts
should appear between
the bases
of
Q4
and Q5.
c.
Replace
the
removed
transistor, Q1 or Q2. Meas-
ure
the voltage
at
the
summing
junction
(front
of
R25).
This
should be
approximately
2.5
volts
positive
and
verifies that reference current flows
through
the reference
divider, R25, and CR4.
d.
Repeatedly
apply the
1.
5
volt battery
to the output
connector
in the
same manner
as
in
the
check pro-
cedure
(paragraph 4-43), and measure
the transistor
voltages
to
determine
where
the
voltage transition
stops. Start
from Q1 on
the Series Pass P/C As-
sembly and proceed toward Q7
on the Amplifier
P/C
Assembly.
4-48.
REFERENCE NETWORK
ADJUSTMENT.
If
the
output voltage cannot be calibrated with R26
on
the
Am-
plifier
P/C Assembly
due
to
aging or changes
in
com-
ponents,
it
may
be necessary
to
adjust the
reference
network. Proceed
as
follows:
a.
First, return the network
to the
original configu-
ration
by soldering
in
jumper
wires across
Rl,
R2 and
R3
on
the Switch
P/C
Assembly. One
or
more
of these
jumpers
may
have been removed
in
the original factory calibration.
b.
Connect
the differential voltmeter between
the
cathode
of
CR2
on the Amplifier
P/C Assembly
and chassis
ground,
and measure
the output
of
the
reference
tube, VI.
The
output
of
the reference
tube should be between
83.
3
and
85.
05
volts.
e.
The
transistors
may
be checked by
repeatedly re-
moving Q5 and measuring
for a voltage transition
at
transistor
elements
at
each stage following Q5.
Or, substitute transistors
known
to be
good and
measure
individual
components with
the transistors
removed.
c.
Cut
the
jumper wires across
Rl,
R2
and R3 on the
Switch
P/C Assembly
according
to.
the following
table.
Recalibrate
the
instrument as described
in
paragraph 4-29
following
adjustment
of the
refer-
ence network.
f.
If
the
supply will regulate within tolerance but
the
output voltage value
is
incorrect, check
the
voltage
input to the regulator
and measure
the divider re-
sistors
R8 and
R9,
R4
and R5;
these are ±1% re-
sistors.
4-47.
ERROR
AMPLIFIER. Proceed
as follows
if
the
amplifier
fails the
check procedure.
a.
Set
the
controls
of
the
Model 415B
as follows:
OUTPUT VOLTAGE
All
to
zero
dials
HIGH
VOLTAGE
STDBY/RESET
POWER
ON
POLARITY
Negative
b.
With
the
VTVM
measure
the voltage
between
the
following points on
the
Series Pass
P/C Assembly
and chassis ground.
Remove Q1
or Q2
on
the
Series
Pass
Assembly
so these voltage sources are
not
loaded down.
VOLTAGE CUT JUMPER WIRE
ACROSS RESISTOR
83.20
to
83.52
NONE
83.44
to
83.70 Rl
83.70
to
83.96
R2
83.
94
to
84.20
Rl, R2
84.
20
to
84.46
R3
84.44
to
84.70
R3, Rl
84.70
to
84.96 R3,
R2
84.94
to
85.20 Rl, R2, R3
4-49.
HIGH
VOLTAGE
RECTIFIER.
This procedure
measures
the output
of the
high voltage
rectifier.
a.
Set the
controls
of
the Model
41
5B as
follows:
POWER
OFF
POLARITY
Negative
OUTPUT VOLTAGE
dials
All
zeroes
HIGH
VOLTAGE STDBY/RESET
TEST
VOLTAGE
Junction of
R5 and R7 -170
to
-210
Cathode
CR3
85
to
105
Cathode
CR2
18 to
22
Anode
CR6
99
to
121
b.
Connect the output
of
the
Model
80F-5
Voltage
Divider
to
the input
of
the differential voltmeter
and connect
the divider input to one
of
the
8068
plate
clips;
connect
the negative lead to the top
of
R6
on the
Bleeder P/C Assembly,
Rev.
t
4-7