Wavetek 3000 Instruction Manual page 194

volts . As the output swings down
toward 0,
Q213
turns on and supplies
current to the front-panel UNLEVELED
lamp ; then, .as the output rises toward
+7
volts,
Q213
again turns off and
prevents current flow to the UNLEVELED
lamp .
This
on/off cycle of
Q213
thus
causes the UNLEVELED lamp to flash .
After the
external
RF
signal is
removed,
IC201
can be unlatched by
momentarily removing AC power from the
instrument .
CW/At1 Mode Selection
With the instrument's 140DULATION MODE
switch set to its AM position, mode
select relay
K201
enables remote
selection of either CW or AM modes .
Q212
is an inverter which controls relay
driver
Q211 .
With the
base of
Q212
(J101 pin
30)
grounded,
Q212
is turned
off ;
therefore,
Q211
is turned on and
effectively grounds one side of K201 's
coil . This energizes K201
and opens
its contacts to place the instrument in
its CW mode .
With relay
K201
in its de-energized
(normally closed) position, modulation
signals (DC,
400 Hz,
1 kHz, or EXT .)
from the Modulation Board are applied
through the relay contacts to the Meter
Board where they are combined with
level programming voltage to produce
amplitude
modulation of the Output
Amplifier output . When
K201
is
energized, its contacts open ;
thus,
modulation signals are removed from the
Meter Board and instrument is in `he CW
mode .
RF
Level Programming
The Programmable
Attenuator contains
one
10 dB section and four
20
dB
sections ; however, two of the
2Q
dB
sections are wired together to
provide
40
dB of attenuation . The resulting
four attenuator pads
(10 dB,
20
dB,
40
dB, and 20
dB) can be combined in 10 dB
steps to give attenuation ranging from
0 to
90
dB . The positive terminal of
each attenuator section is connected to
+27
volts
DC ; then, each attenuator
pad
is activated when required by
grounding its negative terminal through
one of four identical inverter/divider
transistor circuits .'
For example, to insert 10 dB of
attenuation, the "1" wire (J101 pin 26)
is grounded by a contact closure or TTL
signal . This turns off inverter
Q210
which then turns on driver
Q209
and
grounds the negative terminal of the 10
dB pad through
R229 .
If the "8" wire
(J101 pin
29) is
grounded,
80
dB of
attenuation will be activated as
follows . The base of
Q204 is
grounded
directly . The base of
Q206 is
grounded
through
CR205,
and the base of
Q208 is
grounded through
CR206 .
This turns off
inverters
Q204, Q206,
and
Q208
which
turns on drivers
Q203, Q205,
and
Q207,
respectively . The drivers ground the
negative terminals of the
20
dB,
40
dB,
and
20
dB attenuator pads through
R226,
8227,
and
R228,
respectively .
Note that
CR205
and
CR206
are
forward-biased
and conduct only when
the "8" wire is grounded . If the
"4"
wire or
"2" wire is
grounded, the
diodes are reverse-biased and
do
not
conduct .
MAINTENANCE
If a malfunction occurs, the
trouble
can be localized and repaired with the
aid of the circuit description and
schematic .
No preventative maintenance is required
for the
RF
Level Programming option ;
however, periodic testing is
recommended to insure proper operation
of the programming and the Protection
Circuits .
The
level programming can be checked
with the following procedure :
NOTE
OPTION 1B