Belar FMM-1 User manual

Broadcast Equipment
FMM-1
FM MONITOR

WARRANTY AND ASSISTANCE
All Belar products are warranted against defects in materials and
workmanship. This warranty applies for one year from
the date or
delivery, or,
in the case of certain major components listed in the
instruction manual, for the specified period. Belar will repair or
replace products which prove
to be defective during the warranty
period provided
that they are returned to Belar. No other
warranty
is expressed or implied. Belar is not liable for
consequential damages.
For any assistance,
contact either your Belar Sales Representative
or Customer Engineering Service
at the Belar factory.

Broadcast Equipment
Instructions
FMM-1
FM Monitor
BELAR ELECTRONICS LABORATORY, INC.

TABLE OF CONTENTS
SECTION 1 PAGE
GENERAL INFORMATION ................... 3
1-1 GENERAL DESCRIPTION ............ 3
1-2 PHYSICAL DESCRIPTION ............ 3
1-3 ELECTRICAL DESCRIPTION .......... 4
1-4 ELECTRICAL SPECIFICATIONS ....... 4
1-5 MECHANICAL SPECIFICATIONS ....... 5
1-6 INSTRUMENT IDENTIFICATION ....... 5
1-7 ACCESSORIES .................... 5
SECTION 2 PAGE
INSTALLATION ........................... 7
2-1 INITIAL INSPECTION ............... 7
2-2 CLAIMS ......................... 7
2-3 REPACKING FOR SHIPMENTS ........ 7
2-4 PREPARATION FOR USE ............ 7
SECTION 3 PAGE
OPERATIONS ............................. 9
3-1 INITIAL OPERATION ............... 9
3-2 NORMAL OPERATION .............. 9
3-3 LOCAL OSCILLATOR
FREQUENCY CALIBRATION ........ 9
3-4 TRANSMITTER MEASUREMENTS ...... 9
SECTION 4 PAGE
PRINCIPLES OF OPERATIONS ............... 11
4-1 BLOCK DIAGRAM DESCRIPTION ..... 11
4-2 DETAILED CIRCUIT DESCRIPTION ... 11
4-2-1 Oscillator, Tripier & Mixer Circuit ...... 11
4-2-2 Oscillator, Counter Discriminator
&Amplifier Circuits .............. 13
4-2-3 Amplifier, Metering &
Flasher Circuits
................. 14
SECTION 5 PAGE
MAINTENANCE .......................... 15
5-1 INTRODUCTION ................. 15
5-2 PERFORMANCE CHECKS ........... 15
5-2-1 Power and Oven Check ............. 15
5-2-2 Oscillator Level Check .............. 15
5-2-3 Frequency Meter Amplifier Check ...... 15
5-2-4 Freq Meter Discriminator Check ....... 15
5-2-5 Mod Meter Amplifier Zero Check ...... 15
5-2-6 Modulation Calibrator Check .......... 15
5-2-7 Remote Meter Switch Check .......... 15
5-2-8 Percent Mod Potentiometer Check ...... 15
5-2-9 Modulation Polarity Check ........... 15
5-2-10 Carrier Level Check ................ 15
5-2-11 Operate Check ................... 15
5-2-12 De-emphasis Switch Check ........... 16
5-3 ADJUSTMENTS, CALIBRATION &
5-3-1
5-3-2
5-3-3
5-3-4
5-3-5
5-3-6
5-3-7
5-3-8
5-3-9
5-3-10
5-3-11
5-3-12
TROUBLESHOOTING ............ 16
Power &
Oven ................... 16
Oscillator Level ................... 16
Frequency Meter Amplifier ........... 16
Freq Meter Discriminator
............ 16
Mod Meter Amplifier Zero ....... .... 16
Modulation Calibrator
.............. 17
Remote Meter Switch .............. 17
Percent Mod Potentiometer ........... 17
Modulation Polarity ................ 17
Carrier Level ..................... 17
Operate ........................ 17
De-emphasis Switch ................ 17
SECTION 6 PAGE
REPLACEABLE PARTS ..................... 23
6-1 INTRODUCTION ................. 23
6-2 ORDERING INFORMATION ......... 23
SECTION 7 PAGE
SCHEMATICS ............................ 29
LIST OF ILLUSTRATIONS
1-1
1-2
1-3
1-4
2-1
3-1
4-1
4-2
5-1
5-2
FMM-1 FREQUENCY AND
MODULATION MONITOR .......... 3
FRONT PANEL VIEW ............... 4
REAR PANEL VIEW
................ 4
MECHANICAL DIMENSIONS .......... 5
REAR PANEL CONNECTIONS
........ 6
OPERATING CONTROLS ............ 8
BLOCK
DIAGRAM ................ 10
WAVEFORMS .................... 12
A1 CARD ...................... 18
A2 CARD ...................... 19
5-3
5-4
5-5
7-1
7-2
7-3
7-4
A3 CARD ...................... 20
TOP VIEW, COVER OFF
........... 21
BOTTOM VIEW, COVER OFF ........ 22
OSCILLATOR, TRIPLER & MIXER
CARD A1, SCHEMATiC ........... 30
OSCILLATOR, COUNTER & AMPLIFIER
CARD A2, SCHEMATIC ........... 31
AMPLIFIER, METERING & FLASHER
CARD A3, SCHEMATIC
........... 33
FREQUENCY & MODULATION MONITOR
CHASSIS, SCHEMATIC
........... 35

3
SECTION 1
GENERAL
INFORMATION
1-1 GENERAL DESCRIPTION
The Belar FMM-1 FM Frequency and Modulation Monitor,
Figure 1-1, [FCC Type Approval Number 3-1291 is a
wideband, all solid state FM
monitor designed to meet the
Federal Communications Commission requirements for
measuring the center frequency and total modulation
characteristics of monaural as well as multiplexed FM
transmitters having a center frequency
range of 88 to 108
MHz. In addition, the FMM-1 may be used as a low
distortion and low noise FM demodulator for driving audio
monitor amplifiers and the companion Belar FMS-1 Stereo
Frequency
and Modulation Monitor and one or more
SCM-1 SCA Frequency and Modulation Monitors. The
FMM-1 incorporates a deviation type modulation
calibrator
to insure the accuracy of the modulation readings
at any time.
1-2 PHYSICAL DESCRIPTION
The FMM-1, Figure 1-2, is constructed on a standard 5%
x 19 inch rack mount. Seldom used controls and test points
are located under the hinged front cover bar. Factory
adjustments
are located within the shielded compartments
of the monitor. The AC power input, RF input, and
monitor outputs are located at the rear of the FMM-1
chassis on individual connectors or on rear terminal blocks
as shown in Figure 1-3. The FMM-1 is completely solid
state utilizing all silicon transistors for long, trouble-free
life. The individual circuits
are constructed on military
grade, glass-epoxy, plated printed circuit boards. High
reliability industrial and military grade components are
used throughhout.
Figure
1-1

4
1-3 ELECTRICAL DESCRIPTION
The FMM-1 is a solid state, low sensitivity, crystal
controlled, superheterodyne
FM receiver incorporating a
highly linear and stable pulse counting discriminator that
measures the center frequency deviation and demodulates
the FM transmission. Various metering and testing
provisions are contained within
the monitor to measure
transmitter
output characteristics. These provisions include
a center frequency deviation meter; a peak reading total
modulation meter, switchable to either positive or negative
modulation polarity; a peak modulation light, independent
of modulation polarity, that responds to both positive and
negative directions; metering circuits
to set the incoming
RF level and
to standardize the center frequency deviation
meter with
the calibrating oscillator; a deviation type
modulation calibrator to standardize the modulation level.
Outputs obtained from the monitor include a monaural
output for aural monitoring, a distortion meter test output
[both monaural output and distortion meter output have
front panel switched de-emphasis] , a wideband test output,
four wideband outputs for driving associated multiplex
demodulators, an AM noise diode output, and an incidental
AM noise diode output . FCC Type Approved remote
metering
of the FMM-1 may be externally provided for the
center frequency deviation meter, modulation meter, and
peak light.
1-4 ELECTRICAL SPECIFICATIONS
RF Input Sensitivity . . ............... . 0.2 to 10 volts RMS.
RF I
nput Impedance . .. . . . .. ..... .. .. ... . ... 50 ohms .
RF Frequency Range ......... .... .. . ..... 88-108 MHz.
Deviation Meter Range .. ..... . .... .. ...... .... ±3 kHz .
Modulation Meter Range .... ....... . 133 % [100% at 75 kHzl.
Modulation Calibrator ......... .... ..... 100% at 75 kHz.
Modulation Meter Accuracy . .... Better than 5% over entire scale.
Peak
Modulation Indicator . .......... .. . . . .. 50 to 120 %.
Frequency response . . ...... ... .. . .± 0.1 db, 50-75 , 000 Hz,
3 db down at 180 kHz.
Distortion ........ . .. . ... .... .0.1% max. 50-75,000 Hz.
Signal-to-Noise
Ratio ......... 75 db with 75 usec de-emphasis.
Outputs . .... . . ..... . . ... .. 4 wideband isolated outputs to
drive the FMS-l stereo unit and one or more SCM- l
SCA
units, wideband test output , distortion meter
output, aural monitoring output , AM noise output,
and Incidental AM noise output.
Remote Metering .. .. .... Both carrier deviation and modulation
- ..
meters may be remotely metered, 5000
ohms external loop resistance.
" .... ..,
'" IIli1ff1esc _ __ .(8._ rna ,. .......
11«1 em 1m tIIWIlI ta .. u ~
Figure 1-2
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JI
J,
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J1
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FRONT VIEW
Figure 1-4
1-5 MECHANICAL SPECIFICATIONS
Dimensions ................. 5% x 19 x 11 7/8 inches overall
Detailed Dimensions
....................•... Figure 1-4
Net Weight ............................... 15 pounds
Shipping Weight
........................... 19 pounds
1-6 INSTRUMENT IDENTIFICATION
The instrument is identified by the model number and a six
digit serial number. The model number and serial number
appear on a plate located on the rear panel, Figure 1-3. All
oorrespondence to your Belar representative or to the Belar
factory in regard to the instrument should reference the
model number and complete serial number.
1-7 ACCESSORIES
The Belar FMM-1 FM Frequency and Modulation Monitor
may
be used for the remote monitoring of an FM
transmitter with either the Belar MP-1 Remote Meter
Panel or the Belar RFA-1 RF Amplifier. The MP-1 Meter
Panel contains a peak indicator lamp, a carrier frequency
deviation meter
and a modulation meter, both designed for
5000 ohms IClop resistance. The RFA-1 RF Amplifier
provides pre-amplification and selectivity to permit direct
off-air monitoring
with the FMM-1.

6
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SCA
SCA
C. A.M.
NOISE
INPUT
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MONITOR OUTPUT
(,II +25V
...
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UI
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}' REMOTE
+ MOD. METER
"'"
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J, FREQ. METER
CD
-
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EXT. MOD.
PEAK LIGHT
-
-
19VAC
-
N GROUND

7
SECTION 2
INSTALLATION
2-1 INITIAL INSPECTION
Check the shipping carton for external damage. If the
carton exhibits evidence
of abuse in handling [holes,
broken corners, etc.) , ask the carrier's agent to be present
when
the unit is unpacked. Carefully unpack the unit to
avoid damaging the equipment through use of careless
procedures. Inspect all equipment for physical damage
immediately after unpacking. Bent or broken parts, dents
and scratches should be noted.
If damage is found, refer to
Paragraph 2-2 for the recommended claim procedure.
Keep
all packing material for proof of damage claim or for
possible future use.
2-2 CLAIMS
If the unit has been damaged, notify the carrier
immediately. File a claim with the carrier or transportation
company and advise Belar
of such action to arrange the
repair or replacement of the unit without waiting for a
claim
to be settled with the carrier.
2-3 REPACKING FOR SHIPMENT
If the unit is to be returned to Belar, attach a tag to it
showing owner and owner's address. A description
of the
service required should be included
on the tag. The original
shipping carton and packaging materials should be used for
reshipment.
If they are not available or reusable, the unit
should be repackaged in the following manner:
a. Use a double-walled carton with a minimum test
strength
of 275 pounds.
b.
Use heavy paper or sheets of cardboard to protect all
surfaces.
c. Use at least 4 inches of tightly packed, industry
approved, shock absorbing material such as extra firm
polyurethane foam or rubberized hair. NEWSPAPER IS
NOT SUFFICIENT FOR CUSHIONING MATERIAL.
d. Use heavy duty shipping tape to secure the outside of
the carton.
e.
Use large F RAG I LE labels on each surface.
f. Return the unit, freight prepaid, via air freight. Be sure
to insure the unit for full value.
2-4 PREPARATION FOR USE
The FMM-1 Frequency and Modulation Monitor is
designed to be mounted in a standard 19-inch rack mount.
When mounted
in a rack, a slight air space should be
provided above and below
the unit as the heat generated by
the crystal oven should be dissipated. When the monitor is
mounted above high heat generation equipment such as
vacuum-tube power supplies, consideration should
be given
to cooling requirements which allow a free movement of
cooler air through and around the FMM-1. In no instance
should the ambient chassis temperature be allowed to rise
above
50 degrees C [122 degrees F). Mount the FMM-1 to
the rack mount using four No. 10 screws and four No. 10
countersunk finishing washers.
The Model FMM-1 requires a 105
to 125 VAC single
phase,
50 to 60 Hz power source. Consult Belar for
operation with
other power sources. Attach a three wire,
grounded line cord to TB 1 with the ground wire to terminal
2 and the AC line wires to terminals 1 and 3.
Connect a
50 ohm coaxial cable [RG-58) between the
monitor probe on the transmitter [or RF amplifier) and
the
RF input connector J7, at the rear of the main chassis.
CAUTION: DO NOT APPLY MORE THAN 10 VOLTS RF
TO THE MONITOR OR THE RF INPUT LEVEL
CONTROL MAY BE DAMAGED.
If desired, connect external aural monitoring amplifier to
terminals 1 and 2 on TB2. Note that this is an unbalanced
600
ohm output with terminal 1 grounded. A remote
center frequency deviation meter and remote modulation
meter may be connected to terminals 7, 8 and 5, 6
respectively, if desired. Observe the proper polarities
[terminals 6 and 7 are positive) and note
that the external
loop resistance not including meters must be 5000 ohms.
These meters must
be obtained from Belar Electronics
Laboratory, Inc. in order to comply with FCC regulations
on remote metering. A remote peak modulation lamp may
be connected
to terminals 9 and 10. CAUTION: DO NOT
SHORT TERMINAL 9
TO GROUND. The remote meters
and lamp are contained
in the MP-1 Remote Meter Panel.

8
DS3 · POWER LIGHT
DS2· PEAK MOD. LIGHT
DS1 . OVEN LIGHT
S6· CAR. LEVEL
S5· REMOTE METERS
S2 ·MOD. CAL
J9 . WIDE BAND TEST
S2· FREQ. CAL
RS· MOD. METER ZERO
Figure 3-1
1. POWER SWITCH-When depressed turns the unit on. Power is
applied to the crystal oven from the line and is independent of the
power switch.
2. POWER
INDICATOR-Lower amber light between the meters
indicates that the unit is turned on. .
3. OVEN
INDICATOR-Upper red light between the meters
indicates that heat is being applied in the crystal oven.
4. RF
SWITCH-When depressed indicates the RF level on the
percentage modulation meter .
5. REMOTE
SWITCH-When in off [released) position removes
both metering circuits from the remote metering terminals and
substitutes the equ iva lent resistances.
6. OSCI LLATOR
SWITCH-When depressed indicates the oscillator
level
on the percentage modulation meter.
7. FUNCTION SWITCH-When in OP position disables all
calibration circuits
and places the unit in operation for measuring
frequency deviation and total modulation.
8. FUNCTION SWITCH-When in AMP BAL position, the inputs to
the frequency differential amplifier are shorted, allowing it to be
calibrated.
9. FUNCTION SWITCH-When in FREO CAL position, the 650
kHz calibrating oscillator is turned on and applied to the pulse
counter frequency discriminator allowing it to be calibrated.
10. FUNCTION
SWITCH-When in MOD CAL position applies a
standard deviation to the monitor to check modulation calibration.
11 . FREO ZERO POTENTIOMETER-Standardizes the width of
the output pulse of the pulse counter discriminator to read zero in
function 9 above.
12 . AMP BALANCE POTENTIOMETER-Adjusts the DC balance
of the frequency differential amplifier in function 8 above.
13. MOD METER BALANCE- Adjusts the percentage modulation
meter to read zero with no modulation.
14. DE-EMPHASIS SWITCH-When released removes' the 75 usec
de-emphasis
from the monitoring amplifier. This is also effective on
the audio test output jack.
15. POLARITY
SWITCH-Allows the percentage modulation meter
to read either positive or negative modulation polarities. Depressed
it reads positive, released it reads negative polarities.
16 . PERCENT-MODULATION POTENTIOMETER-Pre-sets the
peak modulation lamp to flash at the indicated modulation setting.
This circuit is independent of modulation polarity and can be
activated by either a positive or negative modulation peak or both.
17. WIDEBAND TEST JACK-Parallels the wideband outputs to
the Add-On FMS-1 Stereo and SCM-1 SCA units. Permits tests to
be made on the output of the counter-discriminator such as linearity
and stereo composite waveform tests.
18. AUDIO TEST JACK - Test output from the monitoring
amplifier. Permits linearity tests, frequency response tests, and FM
noise tests to be made from the front panel, with de~mphasis in or
out according to function 14.
19. FREO ADJUST-Adjusts the frequency of the local oscillator.
THIS MUST
BE ADJUSTED WITH AN INSULATED ALIGNMENT
SCREWDRIVER.

9
SECTION 3
OPERATION
3-1 INITIAL OPERATION
The following procedure should be followed for placing the
unit into initial operation. Refer to Figure 3-1 for location
of the control functions:
1. Before turning the unit on, depress the AMP BAL switch
and release
the REMOTE METER switch.
2. Depress the POWER switch and allow a 15 minute
warm-up.
3. Depress
the OSC switch; the reading on the percentage
modulation meter should be approximately 100% or more.
4_ Turn the RF level control on the back of unit maximum
counterclockwise. Apply RF input
to the RF input jack.
Depress
the RF switch and adjust the RF level control until
the percentage modulation meter reads 100%. The monitor
will operate with as little as 20%, but for AM noise
calibration, the 100% level is used.
5. With
the function switch in AMP BAL, adjust AMP BAL
POTENTIOMETER to read center zero on the carrier
deviation meter and adjust the MOD ZERO
POTENTIOMETER to read zero on the modulation meter.
6. With
the function switch in FREO, adjust FREO CAL
POTENTIOMETER to read center zero on the carrier
deviation meter.
7. Depress
the MOD CAL switch; the modulation meter
will read 100% to verify the accuracy of the calibration.
8. Depress OP switch and the monitor is now ready for
operation.
3-2 NORMAL OPERATION
For normal operation, leave the FMM-1 in OP [operate]
position. Changes
in RF level will not affect the accuracy of
the unit. It may be necessary to occasionally adjust the
FREO CAL POTENTIOMETER as in step 3-1-6 above.
The PEAK
MOD POTENTIOMETER is usually set to 100%
so
that the PEAK LIGHT will flash at a modulation peak of
100% or greater. Since this indicator is independent of
modulation polarity [i.e., it responds to both positive and
negative peaks], it may flash when the modulation meter
does not indicate
the peak. The modulation meter polarity
is switched by S4.
Note that when the MOD CAL switch is depressed, the
calibrating signal is applied not only to the metering circuit
but also
to the peak light and monitoring amplifier. Hence
the 60 Hertz square wave tone will be heard in an aural
monitoring amplifier.
3-3 LOCAL OSCILLATOR
FREQUENCY CALIBRATION
The FMM-1 is furnished adjusted to the customer's
frequency. The monitor may be calibrated against an
external frequency standard as follows: The transmitter is
first set exactly to the assigned frequency using an outside
frequency measuring service. Measure transmitter frequency
as per steps 5, 6 and 8 under OPE RATION, Paragraph
3-1.
If the indicated center frequency deviation is not zero, the
local oscillator frequency may be adjusted with the crystal
tuning capacitor C5 [through the front panel] to bring the
deviation to zero.
3-4 TRANSMITTER MEASUREMENTS
Normal transmitter proof-of-performance measurements
may be made with
the FMM-1. Frequency response,
distortion, and noise measurements may be made through
the front panel AUDIO TEST jack J8. Five volts RMS is
available at 100% modulation so that most distortion and
noise analyzers may be used. Measurements may be made
with
or without de-emphasis by activation of S3. The
modulation meter has a flat frequency respol'}se
characteristic so that with a pre-emphasized transmitter, the
audio input level will have to be adjusted according to the
standard 75 usec pre-emphasis curve.
AM noise measurements may be made at J6 on the back
panel. With the RF level at 100%, the normal output of J6
for 100% AM is 0 db [0.78 volts] into a high impedance
[500K
or greater] . Hence a standard AC voltmeter such as
contained
in a distortion analyzer may be used.

10
OSCILLATOR-MIXER
ASSEMBLY Al
I
-- --
--
I I
-- -- --
-- -- --
--
--
I I I
RF
MIXER
650 KHZ INPUT
INPUT
LIMITER
SCHMITT
MONQI
Q3 I -
TRIGGER
MULTIVI
88-108 MHZ
I
~
Q2, Q3
I Q4, Q5
06, C
I I 1
FREQUENCY
I
c:
TRIPLER
CRYSTAL
I
OSCILLATOR
VOLTAGE
87-108 MHZ
I
REGULATOR
Q2 I
650 KHZ
018, Q19, Q20
I
Ql
I L
I
CRYSTAL
--
-- -- -- --
--
-- ---
OSCILLATOR
I
29-36 MHZ
I
Ql
+15V
L
--
--
-~
--
....
I
--
--
--
--
--
----
-- --
\
I PHASE
VOLTMETER
+25V
,.
SPLITTER
AMPLIFIER
~
Ql
Q2, Q3,-Q4
~
I
I
PRE-REGULATED
PHASE
SCHMITT
,
~
POWER SUPPLY
SPLITTER
COMPARATOR
Ql, Q2, Q3 I
Q13
Qll, Q12
,
I
MONITOR
AMPLIFIER
I Q15, Q16
Q17, Q18
L
--
--
--
-- ----
--
--
c
;...,. PERCEN-
~ MODULATI
Figure 4-1

COUNTER ASSEMBLY A2
MONOSTABLE
-
MULTI VIBRATOR
BUFFER
-
010
-
06, 07,08
DIFFERENTIAL
BUFFER AMP
09
013,014,015
Q16,017
-
--
--
-- --
--
--
--
AMPLIFIER ASSEMBLY A3
TER
IER
·04
TT
HOR
112
f' PERCENT
MODULATION
PEAK
RECTIFIER
CR1
MONOSTABLE
MULTIVIBRATOR t--J--t
07,08
DC
AMPLIFIER
05,06
LAMP
SWITCH
09
LOWPASS
FILTER
FL1
--
~
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~
----
AMPLIFIER
011, 012
-- --
lI ,
I
I
...
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_J
MODULATION
METER
PEAK
LIGHT
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FREO .
DEV.
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2 3 4
BASEBAND OUTPUTS

11
SECTION 4
PRINCIPLES OF OPERATION
4-1 BLOCK DIAGRAM DESCRIPTION
Figure 4-1 is a simplified block diagram of the FMM-1
FM Frequency and Modulation Monitor. The signal paths
are shown
but the detailed switching circuitry has been
omitted for clarity.
The incoming RF sample
is applied to the mixer, A1Q3,
along with the tripled local oscillator frequency to form an
intermediate frequency
[I F] of 650 kHz. This signal is a
fully modulated FM signal [Figure 4-2-1] centered
around
650 kHz and is applied to the pulse·counter
discriminator assembly Card A2.
The limiter amplifies and removes any
AM component from
the IF signal. The signal is squared by the Schmitt trigger,
whose
output is differentiated to form a sharp trigger
[Figures 4-2-2 and 6] to drive the monostable
multivibrator, A2Q6, 7 and 8. The monostable
muItivibrator generates a pulse of fixed length and
amplitude [Figure 4-2-3] each time it receives a trigger.
Thus
the output of the multivibrator is a series of pulses
with a fixed length and amplitude whose spacing depends
on
the incoming frequency. Figure 4-2-7 illustrates this
output with an FM modulated signal. Note how the spacing
increases and decreases as
the frequency is deviated about
650 kHz. This output is integrated by the low-pass filter
whose average AC output is equivalent to the original FM
modulation. The output of the monostable multivibrator is
also applied to the buffer amplifier A2Q9 and integrated by
an RC network to provide an average DC signal
proportional
to the carrier center frequency.
This
DC signal is amplified by the differential amplifier and
applied to the carrier deviation meter. The output of the
integrating filter is amplified and applied to the modulation
metering and peak flasher circuits on Card A3.
The modulation metering circuit consists
of a phase splitter
to allow either the positive or negative modulation polarity
to be selected, a feedback amplifier, a peak diode detector
circuit, and current amplifier
to drive the modulation
meter. The peak diode detector circuit has a very short
charging time constant
to allow the modulation meter to
accurately respond to complex waveforms of multiplex
signals as
well as short duration bursts of program material.
The flasher circuit consists of an amplifier, phase splitter,
Schmitt voltage comparator, and monostable multivibrator.
The signal
is split by the phase inverter and both phases are
applied to the Schmitt comparator which has a dual input.
The comparator will only respond
to positive levels that
exceed a given value determined by the setting of the
percent modulation control. But since the phase inverter
inverts the negative modulation, each input of the
comparator receives a positive going signal-one
corresponding to the positive modulation and one
corresponding
to the negative modulation, thus making it
independent
of modulation polarity. Each time the level
exceeds the pre-set level, the Schmitt comparator supplies a
pulse to the monostable multivibrator. The width of the
pulse formed by the multivibrator is set to 3 seconds
duration as required by
the FCC. The multivibrator turns
on
the transistor switch A3Q9 to allow the peak lamp to
flash.
The monitoring amplifier is a feedback amplifier with
push-pull output to provide a low distortion signal for aural
monitoring and audio tests. De-emphasis is accomplished by
controlling the frequency response of the internal gain and
feedback loop.
The supply voltage is regulated to 25 volts by the
pre-regulator [Q1, Q2, and CR6]. The supply to the pulse
counter and oscillator mixer circuits is further regulated by
the precision 15 volt regulator [A2Q18, A2Q19, A2Q20,
and A2CR9].
4-2 DETAILED CIRCUIT DESCRIPTION
4-2-1 OSCILLATOR, TRIPLER
AND MIXER CI RCUIT
The incoming RF is attenuated by R18 [RF level] and
applied to pin 5 of the Oscillator, Tripier and Mixer Card.
Diodes A1
CR 1 and A1 CR 2 prevent excessive RF levels
from overloading the FET mixer A1Q3. Diode A1CR3 is
used to measure the RF level and its DC output is applied
to the modulation meter when S6 [CARRIER LEVEL] is
depressed.
The crystal oscillator
is a modified Clapp-Gouriet oscillator.
This type of oscillator circuit is known for its frequency
stability. The feedback ratio is determined by the ratio of
A1C3 and A1C4. Since these capacitors are large in
comparison to the transistor A 1Q1 capacities, the transistor
has little effect on
the frequency. The crystal is connected
to pins 7 and 8.
The series tuned circuit A1C1, A1L1 forces
the crystal to
operate in the third overtone mode. The crystal is stabilized
at a temperature of 75 degrees C by the oven Y1. Variable
Capacitor C5 [FREQUENCY ADJUST] adjusts the crystal
frequency to that required by the channel frequency.
The
output of the crystal oscillator is multiplied by 3 in the
tripler stage A1Q2. Its final frequency is then 650 kHz
above
the incoming RF carrier frequency and is mixed in
A1Q3 to produce a difference frequency of 650 kHz. The
output of the mixer is filtered by the low-pass filter A1C12,
A1RFC5, and
the cable capacity interconnecting pin 2 to
the input of Card A2.

12
2 3
4 5 6
7 8 9
10
Figure 4-2

4-2-2 OSCILLATOR, COUNTER
DISCRIMINATOR AND AMPLIFIER
CIRCUITS
When the operate [OP] switch S2 is depressed, 15 VDC
from pin 7 is applied to pin 4 to turn on diode A2CR 1 so
that the 650 kHz intermediate frequency, Figure 4-2-1, is
applied to the limiter, A2Q2 and 3. This stage amplifies and
removes any amplitude modulation component
that may be
present on the signal. The Schmitt trigger A2Q4 and 5
squares the signal by developing a pulse each time
the signal
crosses the zero axis in the positive direction. The output of
the Schmitt trigger is differentiated, Figure 4-2-2, and
applied to the monostable multivibrator, A2Q6, 7, and a
through diode A2CR4.
The monostable multivibrator differs from the conventional
multivibrator
in that the timing capacitor A2C16 is charged
through a constant current source, A2Q7, instead
of a
resistor. Zener Diode A2CR5 regulates the voltage to the
base of transistor A2Q7, and silicon diode A2CR6 provides
temperature compensation for
the emitter·base junction of
A2Q7. Potentiometer, R6 [FREQ CAL], in series with R5
[COARSE FREQUENCY CAL] connects the pins 9 and 10
to set the current through A2Q7. The current through
A2Q7 sets
the slope of the charging current of the timing
capacitor A2C16 which determines
the pulse width of the
mu Itivibrator. This modification of the multivibrator
greatly increases both its stability and linearity when
u~d
as a pulse counter discriminator.
The output of the monostable multivibrator, Figure
4-2-3, is buffered by an emitter follower A2Q10 and is
integrated by the low-pass filter FL1, Figure 4-2-4. This
filter counts [averages] the number of pulses over a unit
time interval by filtering
out the 650 kHz pulses and only
passing the modulation, Figure 4-2-9. The output of the
low-pass filter is amplified by A2Q11 and buffered by the
emitter follower A2Q12. The modulation
output [baseband
output]
is taken off pin 12 to drive subsequent portions of
the monitor.
The
output of the monostable multivibrator is also buffered
by transistor A2Q9. The emitter of A2Qa
is direct coupled
to the base of A2Q9. Diodes A2CR7 and 8 form the
emitter load
so that the linearity of the multivibrator is
preserved. This type of coupling decreases the rise time of
the pulse output of A2Q9 and enables transistor A2Q9 to
be driven between cut-off and saturation
to form a
precisely defined rectangular pulse of maximum stability
for frequency measurements.
The
output of transistor A2Q9 is integrated by the RC
network A2R50 and A2C27 to provide a DC that is
proportional to frequency. This DC is compared with the
reference DC from the precision voltage divider, A2R40
and A2R41, by
the differential amplifier A2Q13-17. Any
difference
in voltage then corresponds to a frequency
deviation and
is amplified by the differential amplifier and
applied to the carrier deviation meter through pins 16 and
20. A2C26 couples
the unfiltered modulation to the
reference input of the differential amplifier to prevent low
13
mod ulating frequencies from affecting the frequency
reading. The reference
DC voltage is derived from the same
15 volt supply that powers the monostable multivibrator
to
form a bridge circllit so that the frequency measurement is
relatively independent of supply voltage.
The 15 volt regulator is the series type to provide both
voltage regulation and a low impedance to power the A2
Card. A2Q18
is the pass transistor and A2Q19 and 20
amplify the error difference between the output and
reference zener diode, A2CR9. A2R52 sets the
output to
15 volts.
The calibrating oscillator A2Q1 is a conventional Colpitts
crystal oscillator.
When the FREQ CAL switch S2 is
depressed, 15 VDC from pin 7 is applied to pin 3 which
supplies power to the calibrating oscillator and also turns
on diode A2CR2
so that the 650 kHz calibrating signal is
applied to the limiter, A2Q2 and A2Q3. Note that diode
A2CR 1 is now turned off in this mode of operation. The
calibrating signal allows the pulse width of the monostable
multivibrator
to be standardized to correspond with the DC
reference level of the differential amplifier.
Modulation calibration
is accomplished by gating the 650
kHz calibrating signal on and off through
the limiter. When
the MOD CAL switch S2 is depressed, the calibrating
oscillator is turned on as before. 19 volts, 60 Hertz is also
applied to pin 2 to gate the limiter stage A2Q3 on and off
at a 60 Hertz rate. The effective
FM frequency deviation is
from 0 to 650 kHz or 650 kHz peak to peak; the 650 kHz
deviation
is reduced to 150 kHz by the precision resistance
divider A2R38 and A2R39. The square wave
output from
pin 13, through switch S2, is applied to the Amplifier Card
Assembly A3 and the Composite Output Jacks J 1-4.
Capacitor A2C22 removes the overshoot from the leading
edge of the square wave.
25
VDC is supplied to pin 1 through R4, on the main
chassis, and
to pin 11 to power the buffer A2Q10. R4
drops
the 25 volts to pin 1 to approximately 21 volts to
reduce the power dissipated in the series regulator A2Q1a.
4-2-3 AMPLIFIER, METERING
AND FLASHER CIRCUITS
The inputs to the monitoring amplifier, metering circuit,
and peak flasher circuit are individually calibrated. The
modulation metering circuit consists of a phase splitter to
allow either the positive or negative modulation polarity to
be selected, a feedback amplifier, a peak diode detector
circuit, and current amplifier
to drive the modulation
meter. The baseband signal is applied to the phase splitter
A3Q1 to allow either the positive or negative modulation to
be selected by switch S4
[MOD POLARITY] on main
chassis. Potentiometer A3R5 adjusts
the gain on the
negative polarity
to exactly match the positive polarity.
The wid eba nd feedback amplifier consists of three
transistors A3Q2, 3 and 4. Potentiometer A3R 15 adjusts
the gain of the amplifier
to that value required for
calibration. Diode rectifier A3CR 1 rectifies the positive half
of the signal to charge the capacitor A3C7 to a DC level

14
corresponding to peak value
of the signal. The charging
time constant
is extremely short and is determined by the
low output impedance of the feedback amplifier, diode
resistance and A3C7. This short time constant allows the
modulation meter to accurately respond to complex
waveforms of multiplex signals as well as short duration
bursts
of program material. Resistor A3R20 controls the
discharge time of A3C7.
Field-effect transistor A305 provides a high impedance to
the rectifier circuit and transistor A3Q6 provides the
current gain to drive the modulation meter. Note
that pins
12, 13 and 14 are connected to the MOO METER ZERO
potentiometer, R8, on the main chassis to form a bridge
circuit. R8 balances
the bridge for zero current with no
signal. With a signal, the voltage increases on the emitter of
transistor A306 to inbalance the bridge and current flows
through resistors A3R24 and 25. A sample of the current
through A3R24
is applied to the internal modulation meter
M2 in series with A3R23; pins 10 and 11 connect to the
modulation meter via switches S6 and S7. Resistor A3R23
controls both the damping and the rise time of the
modulation meter. When a remote meter is used to read
modulation, a sample of the current through A3R25 is
applied to the remote meter. Pins 11 and 13 connect the
remote modulation meter
via the REMOTE METER switch
S5. An external 6.2K ohm resistor must be used in series
with the remote meter for correct damping and rise time.
This resistance may include the line resistance.
The peak flasher circuit consists
of an amplifier, phase
spli'tter, Schmitt voltage comparator and monostable
multivibrator. The baseband signal
is applied to the low
gain ampli(ier A3014 which is direct coupled to the phase
splitter A3013. Potentiometer A3R49 sets the span for the
PERCENT-MODULATION potentiometer R9 on the front
panel. The Schmitt comparator has a dual input, A3011
and 12 to accept both negative and positive modulations
respectively. The PE R CENT-MODULATION
potentiometer R9 is connected to pins 15, 16, and 17 to set
the firing
level of the comparator. Hence, each time the
modulation exceeds, the pre-set level, the Schmitt
comparator
iires and develops a pulse to trigger the
monostable multivibrator. The monostable multivibrator
A307 and 8 produces a rectangular pulse of three seconds
duration which drives the lamp switch
A309. The PEAK
MOD light DS2 is the collector load for transistor A309.
The power for the light is supplied by rectifier CR 1 and
capacitor C1. A remote
PEAK MOD light is driven by the
same power supply and switch and may be connected to
terminals TB2-9 and 10.
The monitoring amplifier is a three stage feedback amplifier
to provide a low distortion signal for both aural monitoring
and audio tests. The baseband
signal is applied to the input
stage
A3018 which both amplifies the signal and sums the
feedback voltage
in the emitter. Transistor A3017 provides
additional amplification to drive the output transistors
A
30 15 and 16. Since the output transistors are a
complementary pair, they operate in push-pull. Diodes
A3CR4 and 5 provide forward bias
to allow the output
transistors to operate class AB.
Feedback is taken from the output and applied to the
emitter of the input stage through A3R57.
When terminals
24 and 26 are connected to each other and terminals 23
and 27 are connected
to each other, the feedback follows a
75 usecond pre-emphasis curve so'that the resultant
output
is de-emphasized according to a 75 usecond curve. A3C22
controls the gain and phase of the amplifier so that it is
unconditionally stable. The DE-EMPHASIS switch S3
makes the necessary connections. A3R51 provides the 600
ohm output impedance to drive an aural monitoring
amplifier and A3R52 provides the 10K ohm output
impedance for audio tests.
The main power supply consists
of a full wave bridge
rectifier followed by a voltage regulator. Transistor
01 is
the pass transistor and is driven by the current amplifier 02
which has its base referenced to zener diode CR6. Diode
CR7 provides short circuit protection along with R3.
When
excessive current is drawn from the regulator, the voltage
drop across R3 along with the emitter-base voltages of 01
and 02 exceeds the voltage drop across CR7 and the
current
is limited to a safe value to prevent damage to the
transistors. Diode
CR 1 and capacitor C1 provide power to
operate the PEAK MOD light.

15
SECTION 5
MAINTENANCE
5-1 INTRODUCTION
This section contains maintenance and service information
for
the FMM-l Frequency and Modulation Monitor.
Included are Performance Checks, Adjustments and
Calibration Procedures and Troubleshooting Techniques.
5-2 PERFORMANCE CHECKS
The FMM-l is self-checking to a degree. Before performing
the check procedure, release all push buttons [out
positionl depressing or leaving depressed the AMP BAL
switch S2 and the MOD POL switch S4. No connections
should be made
to the back terminals or connectors except
for the line cord
to TB 1.
5-2-1 POWER AND OVEN CHECK
With
AC power connected to the FMM-l and the power
switch off [releasedl,
the oven light DSl should cycle on
and off approximately every
30 seconds after initial
warm-up. When
on, heat is applied to the oven. Depressing
the
POWER switch Sl turns the unit on, and power light
DS3 indicates that the power is on.
5-2-2 OSCILLATOR LEVEL CHECK
Depressing
the OSC level switch S7 indicates the oscillator
level on the MODULATION meter M2. The reading of the
level should be greater than 100% and should be noted for
future reference.
5-2-3 FREQUENCY METER AMPLIFIER CHECK
Depress
the AMP BAL switch S2 and adjust AMP BAL
potentiometer R7 maximum clockwise to maximum
counterclockwise;
the FREQUENCY meter Ml poiilter
should go off scale in the positive and negative direction
respectively. Return
the pointer to zero for normal
operation.
5-2-4 FREQ METER DISCRIMINATOR CHECK
Depress
the FREQ CAL switch S2 and adjust the FREQ
CAL potentiometer R6 maximum clockwise
to maximum
counterclockwise;
the FREQUENCY meter Ml pointer
should go off scale
in the positive and negative direction
respectively. Return
the pointer to zero for normal
operation.
5-2-5 MOD METER AMPLIFIER ZERO CHECK
Depress
the AMP BAL switch S2 and adjust the MOD
ZERO potentiometer R8 maximum clockwise to maximum
counterclockwise;
the MODULATION meter M2 pointer
should move
in a positive and negative direction about zero.
Return
the pointer to zero for normal operation.
5-2-6 MODULATION CALIBRATOR CHECK
Depress the
MOD CAL switch S2. The MODULATION
meter M2 should read 100%. The FREQUENCY meter Ml
may move off from zero
to plus or minus a few hundred
cycles.
5-2-7 REMOTE METER SWITCH CHECK
Depress
the MOD CAL switch S2. The MODULATION
meter M2 should read 100%. Adjust the FREQ CAL
potentiometer R6
to a reading of plus 1 kHz. Depress the
REMOTE METER switch S5. This MODULATION meter
M2 reading should decrease approximately 6% and the
FREQUENCY meter Ml should return to zero. Release the
REMOTE METER switch S5 and the meters should return
to the previous readings. Return the FREQ CAL
potentiometer R6
to normal as in step 5-2-4.
5-2-8 PERCENT MOD POTENTIOMETER CHECK
Depress
the MOD CAL switch S2. Adjust the PERCENT
MODULATION potentiometer R9 to just turn on the
PEAK MODULATION light DS2. The light should turn on
at 100%. The light will continue to flash on and off at a
rate
of 3 seconds on to a fraction of a second off.
5-2-9 MODULATION POLARITY CHECK
Depress the
MOD CAL switch S2. The MODULATION
meter M2 should read 100%. Release the MOD POL switch
S4 and the MODULATION meter should continue to read
100%.
5-2-10 CARRIER LEVEL CHECK
Turn RF
level control R18 maximum counterclockwise.
Apply
RF carrier to the RF INPUT connector J7 [40
milliwatts
is more than sufficient to drive the monitor to
100% carrier level indicationl. Depress RF switch S6 and
adjust
RF level control R18 until the MODULATION
meter M2 reads 100%. If considerable range remains on
R18,
the RF output from the transmitter should be
reduced by adjusting the coupling probe
in the transmitter.
5-2-11 OPERATE CHECK
With
the RF carrier applied as in step 11, depress the
OPERATE switch S2. The FREQUENCY meter Ml will
indicate
the frequency deviation from the assigned channel
frequency. The MODULATION meter
M2 will indicate the
presence of modulation. The PEAK MODULATION light
DS2 will indicate positive and negative modulation peaks
according
to the setting of the PERCENT MODULATION
potentiometer. It may be noted that the MODULATION
meter M2 may not track at all times with the PEAK
MODULATION light while monitoring program material.

16
This is due to the assymetrical nature of certain types of
program material, i. e., the positive and negative peaks are
not equal
in amplitude. Since the PEAK MODULATION
light circuitry automatically selects
the higher of the two
polarities, it can register a peak opposite to the polarity to
which the MODULATION meter is set.
5-2-12 DE·EMPHASIS SWITCH CHECK
With a 15 kHz modulated signal applied
to the monitor, the
monitor amplifier output may be monitored at the AUDIO
TEST jack J8. Depressing
the DE·EMPHASIS switch S3 will
cause a 17 db decrease in output level, and releasing S3 will
return the amplifier to a flat response. Note that the 600
ohm monitoring amplifier output on TB2 is also
de·emphasized by this switch.
5-3 ADJUSTMENTS, CALIBRATION
AND TROUBLESHOOTING
The following guide for adjustments, calibration and
troubleshooting follows the same numbering sequence as
the PERFORMANCE CHECKS for ease of service.
5-3-1 POWER AND OVEN
a. If the oven light DS1 fails to light, check fuse F2
[0.25A] .
b.
If the oven light DS1 lights but fails to cycle on and off,
remove oven from unit. If the oven is cold, check
continuity
of the heater winding between pins 3 and 4 of
the oven. If the 'oven is hot, the thermostat circuit is stuck
closed and
the oven should be replaced with a new unit.
Note
that both malfunctions will result in an indicated
carrier frequency error. The monitor oven should not be
operated with a stuck thermostat as
the crystal may be
damaged from overheating. The monitor may be operated
temporarily with the oven fuse removed.
c.
If the oven light DS1 fails to light but the oven heats,
check
the oven light.
d. If the power light DS3 fails to light, check fuse F1
[0.5A] .
e.
If the power light DS3 lights but the monitor is
inoperative, check the voltage on terminal 3 of TB2 to
ground. Normal voltage is 26 VDC. If the voltage is high
[37
VDC] , Q2 or CR6 is defective. If the voltage is 0, Q1 is
open or a malfunction exists in the pre-regulator.
f.
If the power light DS3 fails to light and the monitor
functions normally, check
the power light.
5-3-2 OSCILLATOR LEVEL
a. If
the oscillator level reads 0, transistor A1Q1 is
malfunctioning.
b.
If the oscillator level reads above 80% but not the
. normal peak, adjust A1L1 for an indicated peak on M2.
c. If the oscillator level will not peak with the adjustment
of A1L
1, the crystal Y1 [in oven] may be defective.
5-3-3 FREQUENCY METER AMPLIFIER
a. If the FREQUENCY meter M1 pointer fails to go off
scale in both the positive and negative direction, transistors
A2Q14 and 15 are saturated and A2R47 should be replaced
with the next higher value [9.1 K or 10K ohms] .
b.
If the FREQUENCY meter M1 pointer fails to move and
the rest of the monitor functions normally, release
REMOTE METER switch S5. Note
that if remote meters
are used and the malfunction
is cleared when the switch S5
is released, a malfunction exists on the remote meter lines.
c. If releasing the REMOTE METER switch S5 does not
clear the malfunction, A2Q13 and
17 are malfunctioning.
5-3-4 FREQ METER DISCRIMINATOR
a. If the FREQUENCY meter M1 pointer fails to go off
scale in both the positive and negative directions, return the
FREQ CAL potentiometer R6
to its midpoint and adjust
the coarse frequency potentiometer R5 to zero M1.
b.
If the FREQUENCY meter M1 is off scale and cannot
be brought on scale with R6, as
in step (a) above, but the
modulation calibrator functions normally as in step 5-2-6,
check the waveform on the collector of transistor A2Q9. A
low capacity probe should be used with the oscilloscope to
preserve the waveshape and the waveshape should be as
shown
in Figure 4-2-3. If the waveshape does not have a
straight base-line as
in Figure 4-2-10, transistor A2Q9 is
not driven into full saturation and should be replaced. Note
that this malfunction can also cause excessive frequency
drift
in the discriminator.
c.
If the FREQUENCY meter M1 is off scale and the
modulation calibrator does not check as in step 5-2-6, but
the unit functions normally in the OPERATE poSition, the
calibrating oscillator is not functioning or the diode switch
A2CR2
is open. Check also that 15 VDC is applied to the
diode anode.
d.
If the unit does not function in the OPERATE position
in step (c) above, the counter-discriminator circuits are
malfunctioning, and the signal may be traced with the aid
of
the waveforms in Figure 4-2. A low capacity probe
should be used with the oscilloscope to preserve the
waveshape.
5-3-5 MOD METER AMPLIFIER ZERO
a. If the MODULATION meter M2 will not zero, and the
modulation calibrator functions but does not indicate
accurately, the bias on transistor A3Q3 is off. Increasing
the value of A3R 16 wi II decrease the meter read ing by
shifting
the zero to the negative direction, and decreasing
A3R 16 will increase the meter reading by shifting
the zero
to the positive direction. A3R 16 should range between 24K
and 30K ohms and
if it does not, replace A3Q5 or A3Q3.

b. If the MODULATION meter M2 reads off scale, check
resistors A3R24 and 25 for
an open circuit.
5-3-6 MODULATION CALIBRATOR
a.
If the MODULATION meter M2 reads in error but is
within 20% for positive polarity [MOD POL switch S4
depressed] and the PERCENT MOD checks as in step
5-2-8, adjust potentiometer A3R15 for the correct
reading
of 100% after zeroing the meter as in step 5-2-5.
b. If both the MODULATION meter M2 and the
PERCENT MOD potentiometer R9 read in error, check the
voltage output of the 15 volt regulator on card A2 and
adjust A2R52 for 15 volts
output if necessary. Usually the
FREQ METER DISCRIMINATOR CHECK will be off in
step 5-2-4 with the 15 volt regulator out of adjustment.
5-3-7 REMOTE METER SWITCH
a. With remote meters connected to the monitor, the
readings of the FREQUENCY meter M1 and the
MODULATION meter M2 should remain unchanged with
the REMOTE METER switch S5 depressed or released. If
the readings do change, check for faults on the remote
meter lines. When
the remote meters are not connected to
the monitor, the readings will change as in step 5-2-7.
5-3-8 PERCENT MOD POTENTIOMETER
a. If the PERCENT MOD potentiometer R9 reads in error,
the knob may be slipped to the correct reading by
loosening the two set screws and retightening after
adjusting.
b. The span
of the PERCENT MOD potentiometer may be
checked by applying a 400 cycle modulated signal
to the
monitor and checking the tracking at the 50% and 100%
modulation points. Adjust A3R49 so that the percentage
difference on
the PERCENT MOD potentiometer is 50%
when
the modulation level is changed from 100% to 50%.
Slip the knob as in step (a) above if it is necessary to
correct the reading at 100% after the span has been
adjusted.
5-3-9 MODULATION POLARITY
a. With a 400 cycle, 100% modulated signal, adjust A3R5
to obtain equal reading on MODULATION meter M2 when
17
the MOD POL switch S4 is cycled from positive to negative.
Note
that the adjustment can be observed in the negative
polarity position.
b.
If the negative polarity if off seriously and the monitor
is noisy, check the pre-regulated power supply as in step
5-3-1-e.
5-3-10 CARRIER LEVEL
a.
If no RF level is observed and the monitor is functioning
normally in the OPERATE position, check diode A1CR3.
5-3-11 OPERATE
a.
If the monitor fails to function in the OPERATE
position and
all other functions are correct, check diode
switch A2CR1. Check also
that 15 VDC is applied to the
diode anode.
b.
If the FREQUENCY deviation is off scale and the
MODULATION meter is normal in the OPERATE position,
check local oscillator peaking as
in step 5-3-2.
c. If the FREQUENCY deviation is off scale and the
MODULATION meter is normal in the OPERATE position,
check
the oven cycling as in step 5-3-1-b. If the oven is
cycling and the transmitter frequency is correct, crystal Y1
[in oven] is defective.
d.
If the monitor fails to function in the OPERATE
position and
the diode switch circuit is functioning, check
transistors A1Q2 and A1Q3.
5-3-12 DE-EMPHASIS SWITCH
a. If DE-EMPHASIS switch S3 does not function normally,
check capacitors A3C20 and 22. In the DE-EMPHASIS
position, capacitor A3C20 is connected to the circuit by S3
switch contacts connecting pins 24 and 26, and capacitor
A3C22
is connected to the circuit by S3 switch contacts
connecting pins
23 and 27.