Wavetek 3000 Instruction Manual page 81

BCD FREQUENCY SWITCHES - Troubles in the
BCD switch
circuits may be caused by a
defective switch, loose or disengaged
switch connector or a broken switch wire .
Five of .the switches utilize four wires
plus a ground to select decimal digits
from 0 through 9 . The 100's MHz switch
uses three wires plus ground, since it
only needs to select digits between 0 and
5 . A "BCD Truth Table", applicable to
each of the silk switches, is given
in
Table 5-3 .
Suspected switch problems can be checked
by referring to Table 5-3 and the Model
3000 Wiring Diagram to determine
which
module pins are grounded for a particular
frequency . For example,
to select a
frequency of 200 .500 MHz, M172 pin 3 is
grounded by selecting
digit 2 on the
100's MHz switch,
and M31 pins 2 and 4
are grounded by
digit 5 on the 100's
kHz switch .
NOTE : 0 Wire Grounded by Switch .
Wire NOT Grounded .
MODULATION TROUBLES -
The Modulation
Board (C316) is the most common
cause
of modulation
problems, particularly
when the
modulating
signal
is lost .
Non-linear amplitude
modulation, at
higher-audio frequencies from an exter-
nal source,
may be caused by the
M10W
output amplifier .
MAINTENANCE
The presence of the. modulating
signal
can be determined as follows :
Set MODE
switch to AM, FREQ to 400 Hz, AM/FM Ver-
nier to 100% and OUTPUT to +3 dBm.
Con-
nect oscilloscope vertical input to MOD .
T .P . The scope
should display a 10 V
peak-to-peak sine wave
at a frequency
of 400 Hz
(period of 2 .5 ms) . Set
FREQ switch
to 1 kHz - scope display
should be a 10 V p-p sine
wave at
a
frequency of 1 kHz (period of
1 ms) .
Failure to obtain the 400 Hz or
1 kHz
signals indicates a defective Modulation
Board .
Connect scope
vertical input to module
M10W pin 15 . The scope
indication
should be a 1 kHz
sine wave with an
amplitude of approximately - 1 .75 V p-p .
Set FREQ
switch to 400 Hz . The scope
should display a 400 Hz sine wave having
a p-p value of approximately
1 .75 V .
Failure to obtain the 400 Hz
or 1 kHz
signals at this point
may be due to a
defective MODE switch on the Modulation
Board, or a broken wire between
the Mod-
ulation Board and the Meter Board .
Connect scope
vertical input to module
M29-1 pin 16, and set MODE switch to FMxl
or FMx100 .
The scope display should be
a 400 Hz sine
wave having a p-p value
of 10 V.
Set FREQ switch to 1 kHz .
The
scope indication should be a 1 kHz sine
wave with an amplitude of
10 V p-p .
Failure to obtain the 400 Hz
or 1 kHz
signals may be due to a defective MODE
switch, or a broken wire
between the
Modulation Board and module M29-1 .
5 .4 .2 Module Replacement
While in many cases the Model 3000 will
work satisfactorily after simply replac-
ing a defective module, to maintain the
high accuracy of which the unit is cap-
able, module replacement should be fol-
lowed by calibration of
the affected
circuits . Table 5-4 lists each module
and the adjustments needed .
The M172, M9W and
M10W modules may be
replaced individually, however, it
is
recommended that these three modules be
5- 11
TABLE 5-3 .
BCD FREQUENCY SWITCHES
Decimal
BCD Wires
Digit
8 4 2 1
0 - - - -
1 - - - 0
2 - - 0 -
3
- - 0 0
4
- 0 - -
5
- 0 - 0
6
- 0 0 -
7
- 0 0 0
8
0 - - -
9 0 - - 0