Circuit Analysis - GE 4EX3A11 Maintenance Manual

IUASTR
II, Executive II,
Custom
MVP
and
Im-
perial equipment, it should normally be in
the
?r+'r
posltion;
f
or
MASTR
Prof
essional
equipment
it should normally be in the
tr-
"
position.
It
may
be necessary to switch
the polarity of the meter while
checking
FIL voltage,
depending upon whether the
radio is installed in a vehicle with
a
positive -ground or negative-ground battery.
"tlig'tr S.u=i
tiv
This switch permits the driver and
PA
current to be
metered
in Royal Professional,
Roya1
Executive,
MASTR
II, Executive II,
Custom
MVP
and
MASTR
Imperial transnitters.
With the range selector switch in
the
l-Volt positionr pressing the high sensi-
t
ivi ty switch
(
56)
bypasses
RI
(
f
0
.2K
ohms
)
and R2 (2430 ohms) with potentiometer
Rg
(25-500
ohms) and R10 (39O
ohms)
.
The
lower resistance in the meter i-nput circuit
permits l00-millivolt
full scale
meter
reading
"
DI
Scriminator
Switch
trushing the
DISC
button instantly
switches the meter from test positions
,Brt through
rrKtr
back to the discriminator
circuit
(position
"A")
. This feature eli-
minates the need for a
second
meter to
monitor the discriminator voltage.
XMTR
TEST
Switch
LB
I.l
-154
When
servicing a transmitter,
transmitter can be easily
keyed
by
the
KITR
TEST
switch.
AUDIO Jacks
DC
VOLTMETER
MEASUREMBNTS
To
use the Test Set as a
DC
voltmeter,
just place the
TEST
SELECTOR
switch in
the
rrvMrt
posi
t
ion
o
Use
the
RANGE
SELECTOR
switch to select the desired voltage
range:
l, 3, 15, 3O,
1OO,
3OO
or
1OO0
Volts.
Con-
nect the test probes to the red
and black
j acks beneath
the meter on the front of
the
Test
Set
"
With the polarity-reversing
switch in
the
r'+rr
positioo, the red test probe j
ack
will be positive and the black jack will
be
negat
j-ve
"
To
quickly
change
the polarity of
the test probes,
j ust
f
lip the
swi-tch
to
the
rr-tr
positiofr
o
CIRCUIT ANALYSIS
The
voltage range desired is selected
by
RANGE SELECTOR
switch 53,
whi-ch
connec
ts
meter MI to
TEST
SELECTOR
switch 52
through
a series string of prec'ision resistors
(nS through
R8)
. 53 switches the positive
and
negative sides of the meter to
eleven
floating pins on 52, which selects the cir-
cuit to
be
metered
"
Di.odes
CRI and
CRz
limit the
meter
overload to approximately six times
the
rated current of the met€rr with less
than
O
"5%
ful1-scale
compression
" As a 1-Volt
instrumeilt, the meter is protected for
a
1OOO
to 1 overload. Howev€r, under this
conditioo,
one
or
more
of the meter resis-
tors
may
be
damaged
"
Due
to the lower resistance in
the
meter circuit,
the meter is
more
susceptible to
damage when
using
the
high sensitivity
(HS)
switch.
Always
check the meter reading before
press
ing the high sensitivity switch.
DISASSEMBLY
To service the Test Set, simply re-
move
the four
screws
holding the rubber
feet and lift off the
back
plate"
CALIBRATION
PROCEDURE
If rneter Ml is ever replac€d, poten-
tiometer
Rg
must be reset according to the
f
ollowing
proced.ure
"
1o
Remove
the back plate
f
rorn the
Test
Set.
OPERATI
ON
the
press
ing
While the Test Set is
connected
to
a
transmitt€r, the
AUDIO
test jacks, otr
each
end
of the set, provide a
conven
j-ent
place
to connect an audio oscillator for
modula-
ting the transmitter. This facilitates
setting ttansmj.tter
modulati.on
levels.
With the Test Set
connected
to a receiver,
the receiver audio output can
be
measured
across the
AUDIO
test jacks.*
An audio
voltmeter or distortion
anaLyzer can
be
easily
connected
here for receiver quieting
or
S
INAD
measurements. Note that
these
j acks are properly spaced to accept
a
standard dual-banana plug, and are labeled
for
MASTR
and
MASTR
II (including
Executive
II and
Custom
MVP).
Microphgng J?ck
The microphone
j acks on the ends of
the Test Set provide convenient places to
connect a microphone or handset for keying
or voice-modulating a
MASTR
transmitter.
The
audio output of the receiver can also
be monitored
by a
handset connected
to
these j
acks
"
* In PortaoMobile receivers before Rev. A,
the
appear
at the
AUDIO
HI jack on the Test
Set
LO
j ack.
2
LO
side of
the
and
the HI
side
receiver audio output wilI
will
appear
at the
AUDIO