Tektronix T912 - Page 44

Adjustments—
T91
2
2.
Vertical
Output
Amplifier
Gain
NOTE
You
should
not
have
to
re-adjust
the
vertical
output
gain
unless
you
have
replaced
the
crt or
other
components,
or
adjustments
have
accidentally
been
altered.
a.
Set
VOLTS/DI
V
(both)
to 5
mV/div
and
Vertical
Mode
to CH
1.
b. Set
Gain,
R126
(see Fig.
4-2),
to
physical
midrange.
c.
Connect
digital
voltmeter
between
P4-9
and P4-11
(see
Fig.
4-4).
Select
range
on
meter
for
at least
500 mV
reading.
e.
ADJUST—
Gain, R4251
(see
Fig.
4-4), for
4-division
display.
f.
INTERACTION—
If
you cannot
adjust
CH
1
and CH
2
Preamplifier
Gain
for4-division
display,
repeat
steps
2 and
g. Disconnect
test
equipment.
NOTE
For
convenience
in
the
following
steps,
set the TIME
base
to
1
ms
(SEC/DIV to 1
ms
and
X1-X10
to XI
)
while
adjusting,
the
generator
for a
5-division
dis-
play.
Then
set
TIME
BASE to
50
p
(SEC/DIV
to
.5
p
and
X1-X10
to
XI
0)
when
observing
or
adjusting
leading
edge
detail.
d. Set vertical
POSITION
control
so trace
is aligned
with
center
horizontal
graticule
line,
Note
meter
reading.
4.
High-Frequency
Compensation
a. Set:
Vertical
Mode
CH 1
e.
Rotate
vertical
POSITION
control
until
meter
reading
has
changed
150 mV
positive
from
reading
in
partd
(trace
moved
toward
top of
screen).
CH 1
AC-GND-DC
CH
2
AC-GND-DC
POSITION
(all)
DC
GND
To
center
display
f. Adjust
Gain,
R126
(see Fig.
4-2),
so trace
aligns
with
third
graticule
line
above center
horizontal
graticule
line.
g.
Disconnect
ditigal
voltmeter.
3, Vertical
Preamplifier
Gain
a. Set:
VOLTS/DIV
(both)
5 mV
AC-GND-DC
(both)
DC
Vertical
Mode
CH 1
b. Connect
a
1
kHz,
20 mV
amplitude
calibrator
(standard
output)
signal
to
CH
1 input via
a
50 Q
unterminated
cable.
Set
CH
1
POSITION
to
center
the
display
vertically.
c.
ADJUST—
Gain, R4151
(see
Fig.
4-4), for
4-division
display.
d.
Move
20
mV
amplitudecalibratorsignal
to
CH 2
input
and set
Vertical
Mode
to CH
2. Set
CH 2
POSITION
to
center
the
display
vertically.
b.
Connect
square-wave
generator
(fast-rise,
-F
transi-
tion)
to
CH 1
input
connector
via
50 G
cable, 10X
attenuator,
and
50 Q
termination
(see Fig.
4
-
5
).
c. Set
square-wave
generator
for 100
kHz,
fast
rise,
and
amplitude
for
5-division
display.
Set
SEC/DIV
to .5 ps,
and
INTENSITY
as
necessary
to view
the
display.
d.
Set
POSITION
and
LEVEL
controls
to
position
the
leading
edge
of
the signal
on
screen.
e.
ADJUST—
R4334, C4334,
R4344,
C4344
(see
Fig.
4-
4),
and
C133
(see
Fig.
4-2), for
best
front
corner
of
waveform
using
low
capacitance
screwdriver.
S.
CH
1
Attenuator
Compensation
a.
Set:
CH
1
VOLTS/DIV
20 mV
CH 1
AC-GND-DC
DC
Vertical
Mode
CH 1
SEC/DIV
X1-X10
POSITION
(all)
1
ms
X10
(fully
ccw)
As
required
REV.
A
APR 1977
4-9