Fluke 5205A Instruction Manual page 51

5205A
Set the autotransformer output
to zero.
Set
the
POWER
switch to
OFF
and
disconnect
both power
cords. Wait
at least
30
seconds
for
the
Power
Supply
to discharge and
disconnect the oscilloscope
voltage and
current probes
from
the instrument.
4-79.
SCREEN VOLTAGE
CALIBRATION
4-80.
Make
the following equipment
changes:
a.
Prepare the
DVM
to
monitor
the
nominal
AC
line
Voltage
and
connect the input
leads across the auto-
transformer output.
b. Prepare the Oscilloscope
for operation with
sen-
sitivity
of 2V/division (corresponding to 20V/division
at the probe
tip), a
time
base
of 20
usec/division and
dc coupling.
c.
Accurately adjust the oscilloscope
probe
AC
com-
pensation using the
oscilloscope
calibrator.
d. Set the
vertical gain
of
the oscilloscope
by
applying
an external
56.57Vrms±l%
(56.01
-
57.13) 10
kHz
signal
to the 10:1 input
probe. Adjust the scope
channel
variable
gain for a display of exactly 8
divisions peak-to*peak
(at
20V/division
sensitmty
equal
to
160V
p-p).
e.
Disable the
5205A
overload
circuits
by connecting
TPiS
OVERLOAD
DISABLE
to
TP19
GND
(SENSE
LOW)
with
a
jumper. The
test
points
can be reached
through
the Preamplifier
shield.
f.
Reconnect
the Auxiliary
Power
line
cord
to
the
nominal
line
voltage
and
the
High Voltage
line cord
to the auto transformer.
4-81. Perform
the calibration using
the following pro-
cedure:
NOTE
For
correct adjustment of
the current
limits
it is
important
to
check
the zero base
line for
drift
both
before
and
after the procedure. If any
drift
occurs
the procedure should be
repeated.
a.
Raise the
autotransformer output
voltage to
nom-
inal plus
ten percent
(1
10%
x
1
15V
= 126.5V).
b.
Apply
an input of 0.45
±2%
volts
rms
(0.441
-
0.459
Vrms)
at
10
kHz
from
the
test oscillator.
c. Set the
5205A
POWER
switch
to
ON.
NOTE
The 5205
A
internal povjer
disipation
is
very high
when
it is
in the
OPERATE
mode.
Maintain
this
status
only
as
long
as necessary to
make
the
re-
quired adjustment.
d. After the
warm-up
period,
set the
5205
A
MODE
siwtch
to
OPERATE.
e.
Adjust R109
ABSOLUTE SCREEN VOLTAGES
LOWER
TUBES
through
the
power
amplifier shield
until
the scope
displays
a
waveform
where
the
flat
portion
of
the negative peak
is
at
exactly
-60
volts
(-3.0
divisions).
f.
Check
the zero base
line setting the
5205A -MODE
switch to
STDBY RESET
and
then back
to
OPER-
ATE. The
adjusted peak
voltage should remain
as
set in step
e
above.
g.
Set the Test
oscillator voltage
magnitude
to
0.39V
rms.
h. Adjust
R35
ABSOLUTE SCREEN VOLTAGES
LT-
PER TUBES
through
the power
Amplifier
shield
until the scope
displays a
waveform
where
the
flat
portion of
the
positive
peak
is
at
exactly
+52
Volts
(+2.6
divisions).
i-
Check
the zero base
line
by
setting the
5205A
MODE
switch to
STDBY RESET
and
then back
to
OPER-
ATE. The
adjusted peak
voltage should remain
as
set in
step
h
above.
j
.
Set the
MODE
switch
to
STDBY-RESET
and
the
POWER
Switch
to
OFF, Remove
the Test
Oscilla-
tor
input to
the
5205A.
Set the autotransformer
output
voltage to zero and
disconnect both
power
cords.
Remove
the
oscilloscope and
DVM
leads.
4-82. POSITIVE
CURRENT
TRIP
LEVEL ADJUSTMENT
4-83.
Make
the following equipment
changes:
a. Insure a
jumper
connects TP408
(Il_) and
TP407
(GND)
on
the Logic
pcb.
Remove
the other
jump-
ers previously
installed
between
test points
on
the
Logic
and
Preamplifier
pcb's. llie
jumper
remaining
disables the negative current
trip
while
setting
the
positive trip
level.
b.
Connect
the
DVM
HI
input lead to
TP411
(1+)
and
the
LO
lead to
TP407 (GND)
on
the Logic pcb.
Prepare the
DVM
to read
less
than 2 Volts
dc.
c.
Reconnect
the Auxiliary
Power
line
cord
to the
nominal
line voltage
and
the High Voltage
line
cord
to the autotransformer.
4-17