Broadcast Electronics AM-10A Manuale utente
TABLE OF CONTENTS
PARAGRAPH PAGE NO.
SECTION I POWER SUPPLY THEORY OF OPERATION
1-1 Introduction 1-1
1-3 General Description 1-1
1-6 AC Input 1-1
1-8 Conventional Rectifier Circuitry 1-1
1-10 Soft-Start Circuit 1-1
1-12 AC ine Detection/Synchronization 1-2
1-15 Soft-Start Control Circuit 1-2
1-18 Power Factor Corrector Circuit Board Control Circuit 1-2
1-20 SCR Controlled Rectifier Circuit 1-5
1-23 Filter Circuit 1-5
1-25 Power Supply Enable Circuit 1-5
1-28 Switching Regulator Circuit 1-5
1-30 ow Voltage Power Supply 1-6
1-31 Switching Regulator Control Circuit 1-6
1-33 Switching Regulator Circuit Operation 1-6
1-34 Power Control/Correction Circuit 1-6
1-38 Fault Detection 1-7
1-43 Crowbar Circuit 1-7
1-47 Power Supply Circuit Grounds 1-8
SECTION II POWER SUPPLY CIRCUIT BOARD MAINTENANCE
2-1 Introduction 2-1
2-3 Safety Considerations 2-1
2-6 First evel Maintenance 2-1
2-8 Cleaning and Inspection 2-1
2-10 Second evel Maintenance 2-2
2-12 Troubleshooting 2-2
2-13 Safety Considerations 2-2
2-14 Removing/Installing a Power Supply Circuit Board 2-2
2-17 Troubleshooting Procedures 2-3
2-18 Component Replacement Procedure 2-4
SECTION III POWER SUPPLY CIRCUIT BOARD PARTS LIST
3-1 Introduction 3-1
SECTION IV POWER SUPPLY CIRCUIT BOARD DRAWINGS
4-1 Introduction 4-1
LIST OF ILLUSTRATIONS
FIGURE TITLE PAGE NO.
1-1 POWER SUPP Y CIRCUIT BOARD 1-3
SIMP IFIED SCHEMATIC
LIST OF TABLES
TABLE TITLE PAGE NO.
2-1 POWER SUPP Y MODU E TROUB ESHOOTING 2-3
3-1 REP ACEAB E PARTS IST INDEX 3-1
1-1
SECTION I
POWER SUPPLY THEORY OF OPERATION
1-1. INTRODUCTION.
1-2. This section presents a general description of the Broadcast Electronics AM-10A/AM-6A
transmitter power supply assembly.
1-3. GENERAL DESCRIPTION.
1-4. DC operating potentials for the RF power modules are provided by power supply assemĆ
blies (refer to Figure 1-1). The power supply assembly consists of: 1) a power supply cirĆ
cuit board and 2) filter and transformer components located on a power supply panel.
One power supply assembly provides dc operating potentials for one power block. The
AM-10A transmitter is equipped with 5 power supply assemblies. The AM-6A transmit-
ter is equipped with 3 power supply assemblies.
1-5. The modular design of the power supply assembly allows the power supply circuit board
to be removed from the transmitter for maintenance. The following text presents a deĆ
scription of the power supply circuit board and the components located on the power sup-
ply panel assembly.
1-6. AC INPUT.
1-7. AC power from the ac input switch is applied through fuses F6 and F7 to power trans-
former T1. Fuses F6 and F7 protect the circuitry from over-current conditions. TransĆ
former T1 consists of: 1) a single primary winding and 2) five secondary windings. The
transformer is designed to provide low-voltage ac samples for application to five convenĆ
tional bridge rectifier circuits.
1-8. CONVENTIONAL RECTIFIER CIRCUITRY.
1-9. AC power from a winding of power transformer T1 is applied to bridge rectifier D11. D11
rectifies the ac potential into an unregulated 30V dc supply for application to the RF power
module power amplifier circuit boards. Capacitor C21 provides filtering for the supply. AC
power from a second winding of transformer T1 is applied to bridge rectifier D10. D10 recĆ
tifies the ac potential into an unregulated +20V dc supply for the power supply circuit
board circuitry. Capacitor C20 provides filtering for the supply. AC power from a third
winding of ac power transformer T1 is applied to bridge rectifier D9. D9 rectifies the ac
potential into an unregulated +20 volt dc supply for application to: 1) the modulator cir-
cuit board and 2) to regulator U3. U3 is a +15 volt dc regulator. The output of U3 routed
for application to the components on the power supply circuit board. AC power from a
fourth winding of power transformer T1 is applied to bridge rectifier D12. D12 rectifies
the ac potential into an unregulated +15V dc supply for application to: 1) the power sup-
ply circuit board and 2) regulator U4. U4 is a +12 volt dc regulator. The output of U4
routed for application to the components on the power supply circuit board. An ac sample
from the winding is routed for application to a soft-start circuit. Capacitor C15 provides
filtering for the supply.
1-10. SOFT-START CIRCUIT.
1-11. An ac sample from the winding of T1 is also routed to a soft-start circuit. The soft-start
circuit is designed to eliminate component stress during turn-on by limiting the current
in-rush. The circuit consists of an ac line detection/synchronization and soft-start control
circuits.
1-2
1-12. AC LINE DETECTION/SYNCHRONIZATION. An ac sample from a winding of transformĆ
er T1 is rectified by diodes D7 and D8 and applied to integrated circuit U6B. U6B funcĆ
tions as a zero phase detector. As the ac line phase approaches zero degrees, U6B will
output a HIGH pulse. The HIGH pulse is applied to: 1) transistor Q2, 2) transistor Q7 of
the soft-start circuit, and 3) ac line detector U5A/U5B. The pulse biases transistor Q2
and optical coupler U2 on. Q2 and U2 will output a pulse each time the ac line phase is
zero. As a result, U2 will output a 120 Hz signal to the controller circuit board.
1-13. U5A and U5B function as an ac line voltage detector. When ac line voltage is present,
U5A will output a OW. The OW allows transistor Q3 to be biased on. With Q3 on, a
+12 volt dc signal is applied to optical coupler U1. When a power supply enable and a
PWM OK signal is applied to U1, U1 will output a reference voltage to a soft-start control
circuit for power supply operation. When ac line voltage is not present, U5A will output a
HIGH, the HIGH biases transistor Q3 off to terminate power supply operation. When ac
power is re-applied, U5B will maintain a HIGH for 100 milliseconds to allow the circuit to
stabilize during turn-on operations.
1-14. In addition to the ac line voltage detection circuit, integrated circuit U6A functions as a
low line voltage detector. When the dc supply is above the threshold at U6A, U6A will
output a OW to bias transistor Q1 off. As a result, a HIGH ac OK signal indicating acĆ
ceptable ac line voltage is applied to optical coupler U9. When the dc supply is below 185
volts, U6A will output a HIGH to bias transistor Q1 on. As a result, a OW ac OK signal
indicating low ac line voltage is applied to optical coupler U9. When the voltage increases
to approximately 190 volts, the output of U6A will go OW to enable the power supply.
1-15. This circuit is also used to detect high ac line voltage potentials. If the ac line voltage is
above approximately 270 volts, transistor Q28 will be biased on. With Q28 on, the input
to U6A will be muted. When the input is muted: 1) the transmitter output power will be
muted and 2) no transmitter fault or emergency condition will be generated.
1-16. SOFT-START CONTROL CIRCUIT. The soft-start control circuit consists of: 1) transistors
Q4 through Q9 and 2) integrated circuit U7. The circuit is designed to generate short
duration pulses in each time the ac line waveform crosses the 0 volt axis. The pulses are
applied to an SCR controlled rectifier to slowly bias the components on during initial start
operations. This operation eliminates the component stress at power-on by limiting the
supply in-rush current.
1-17. The circuit generates the soft-start pulses from two signals: 1) a ramp signal and 2) a
triangle signal. The ramp signal is generated by transistors Q4 and Q5. When ac line
voltage is detected, a +12 volt signal from U1 is applied to transistor Q4. Q4 operates in
association with capacitor C16 and transistor Q5 to generate a ramp voltage. The
triangle signal is generated by transistors Q6 and Q7. Pulses from U6B are applied to
transistor Q7. Q7 operates in association with capacitor C17 and transistor Q6 to gener-
ate a triangle signal. The triangle signal and the ramp signal are applied to comparator
U7. U7 responds by generating a square-wave signal with a short duty cycle when the ac
line phase is zero. The square-wave signal from U7 is applied to soft-start driver transisĆ
tors Q8 and Q9. Q8 and Q9 will slowly bias the rectifier circuit on to limit the current
in-rush.
1-18. POWER FACTOR CORRECTOR CIRCUIT BOARD CONTROL CIRCUIT.
1-19. Transistors Q26 and Q27 control a power factor corrector circuit board (not used in
A-Series AM transmitters). During soft-start operation, ramp voltage will drop below
approximately 3V. When this occurs, the output of transistor Q26 will go OW. This
OW biases transistor Q27 on. With Q27 on, a OW energizes two relays on the power
factor corrector circuit board. With the relays energized, a capacitor is inserted into the
circuit to enable power factor correction.
597-1112-28A
FIGURE 1-1. POWER SUPPLY CIRCUIT BOARD
SIMPLIFIED SCHEMATIC
(1-3/1-4)
COPYRIGHT © 1997 BROADCAST ELECTRONICS, INC
1-5
1-20. SCR CONTROLLED RECTIFIER CIRCUIT.
1-21. The ac line voltage is rectified into a main dc supply for the modulator and amplifier cirĆ
cuitry by an SCR controlled bridge rectifier circuit. Primary ac power for the main dc
supply is applied to ac line filter F 1. F 1 is a modular line filter designed to protect the
circuitry from EMI. The ac from filter F 1 is applied to fuses F1 and F2. The fuses pro-
tect the power supply circuitry from over-current conditions. Metal-Oxide-Varistor
MOV1 prevents damage to the rectifier circuitry from ac line voltage surge potentials.
1-22. The SCR controlled rectifier circuit consists of diodes D15 through D17 and SCRs D13
and D14. The rectifier circuit is controlled by the soft-start control circuit. When power
is required from the circuit, the soft-start circuit will output synchronized ac line pulses
to SCRs D13 and D14. The SCRs will respond by slowly biasing the rectifier circuit on.
The rectifier will output an unregulated and unfiltered dc supply at a maximum of 300V
to an inductor and capacitor filter network located on the power supply panel.
1-23. FILTER CIRCUIT.
1-24. The output of the rectifier circuit is applied to a filter network consisting of inductor 1
and capacitors C24 through C27. The filter is designed to remove the ripple in the supply.
The output of the capacitor network generates the positive leg of the B supply. The B supĆ
ply is the main operating supply for the RF power modules. The negative leg of the B
supply is generated by a switching regulator circuit (refer to the following text).
1-25. POWER SUPPLY ENABLE CIRCUIT.
1-26. The power supply is controlled by a: 1) power supply enable signal from the controller
and 2) power supply mute signal from the modulator circuit boards. When power supply
operation is required, the controller will output a OW power supply enable signal to optiĆ
cal coupler U8. With no mute signals present, U8 will output a HIGH to AND gate U12A.
With a HIGH ac OK signal from U9 indicating the presence of ac power and no power
supply faults, U12A will output a HIGH to U12B. With a HIGH from U21A/U21B, U12B
will output a HIGH to U12C and to Q12. With a HIGH from U14 indicating the crowbar
circuit is off, U12C will output a HIGH after a one second delay to: 1) transistor Q10,
2) AND gate U12D, and 3) NAND gate U21C. The HIGH biases Q12 and U15 on to dis-
able the crowbar circuit. Q10 will respond by routing a HIGH power supply enable signal
to optical coupler U1. U1 will output a dc voltage to enable the power supply soft-start
circuit. AND gate U12D will output a HIGH to transistor Q11. The HIGH biases Q11 on
to enable regulator controller U13 and bias Q13 off.
1-27. When a power supply mute operation is required, an RF power module modulator circuit
board will output a mute signal to optical coupler U8. U8 will output a OW to AND gate
U12A. With a HIGH ac OK signal from U9, U12A will output a OW to U12B. U12B will
output a OW to U12C and to Q12. The OW biases Q12 and U15 off to enable the crowĆ
bar circuit. U12C will output a OW to: 1) transistor Q10, 2) AND gate U12D. Q10 will
be biased off to terminate power supply operation by disabling the drive to the SCR rectifiĆ
er circuit. U12D will disable Q11 which allows a HIGH to disable regulator controller
U13 and bias Q13 on. Q13 will output a OW to disable the fault detection circuit to preĆ
vent erroneous fault indications during mute conditions.
1-28. SWITCHING REGULATOR CIRCUIT.
1-29. The B supply is regulated and controlled by a switching regulator circuit. The switching
regulator circuit generates the - leg of the B supply and consists of: 1) a low voltage pow-
er supply circuit, 2) a power control network, 3) optical coupler U17, 4) inverting buffer
U19, and 5) switching regulator transistors Q21 and Q22.
1-6
1-30. LOW VOLTAGE POWER SUPPLY. A dc operating supply for the optical couplers and the
inverting buffers is generated by bridge rectifier D25. D25 full-wave rectifies an ac po-
tential from ac transformer T1 into an unregulated +20V supply. The supply is applied to
+18V regulator U16. The output of U16 is further regulated to a 5V operating potential
by a resistive divider and a zener diode. The 5V supply is applied to optical coupler U17
and buffer U19.
1-31. SWITCHING REGULATOR CONTROL CIRCUIT. The switching regulator circuit is conĆ
trolled by: 1) regulator controller U13 and 2) a power control/correction circuit. The cirĆ
cuits function in a closed-loop to control the operation of the switching regulator. As a
result, the regulator outputs a precision dc operating voltage at the appropriate level for
application to the RF power modules.
1-32. Integrated circuit U13 functions as the switching regulator controller. U13 is a PWM outĆ
put device designed to produce two out-of-phase square wave signals with varying duty
cycles. The duty cycle is varied in response to the signal from the voltage correction cirĆ
cuit. With a correction voltage present at U13, U13 will output a PWM square wave sig-
nal to optical coupler U17. U17 provides isolation for the transition of the signal from two
different circuit ground potentials. The output of coupler U17 is inverted by inverting
buffer U19.
1-33. SWITCHING REGULATOR CIRCUIT OPERATION. The PWM output of U19 is applied to
the gates of IGBT (insulated-gate-bipolar-transistor) switching regulator transistors Q21
and Q22. The transistors function to regulate the negative leg of the B supply. The out-
put of the transistor switching regulator circuit is applied to filter inductor 2. Protection
of the transistors from switching transients during turn on/off operation is provided by
clamp diode D32. Capacitor C55 provides filtering for the negative leg of the B supply.
The output of the regulator circuit (B- leg) is applied to circuitry on the modulator circuit
board.
1-34. POWER CONTROL/CORRECTION CIRCUIT.
1-35. The switching regulator output voltage is controlled by a PWM (pulse-width-modulated)
signal from the controller. The PWM signal is a 1 kHz square-wave signal with a duty
cycle which varies in response to different power levels. The PWM signal from the con-
troller is applied to optical coupler U22. With a +5 volt signal from the motherboard, U22
will output the PWM signal to transistors Q17 and Q18. Q17 will discharge capacitor C63
when a 1 kHz control signal is present. C63 will output a OW PWM OK signal to optical
coupler U1. Q18 inverts the power control PWM signal. The output of Q18 is applied
through buffer U24C to a low-pass filter consisting of: 1) resistors R115, R116, and R117
and 2) capacitors C75, C76, and C77. The filter converts the power control PWM square-
wave signal into a dc control voltage. The voltage is routed through buffer U24A to U24B.
1-36. U24B functions as a current feedback loop filter. U24B differentially amplifies the dc conĆ
trol voltage and a current sample from the switching regulator output filter capacitor. As
a result, U24B produces a dc control voltage for application to U24D.
1-37. U24D functions as a voltage feedback loop filter. U24D differentially amplifies the control
voltage from U24B and a voltage sample from the B+ leg of the supply. As a result,
U24D produces a dc control voltage for application to: 1) switching regulator controller
U13 and 2) a fault detection circuit. U13 will respond to the correction voltage by chang-
ing the duty cycle of the PWM drive signal to optical coupler U17. The switching regula-
tor circuit will respond by changing the output voltage to a level required by the power
control PWM signal.
1-7
1-38. FAULT DETECTION.
1-39. A fault detection circuit monitors the regulator for four conditions: 1) over-voltage,
2) open-loop, 3) over-current, and 4) over temperature. Over-voltage conditions are
monitored by U23A. U23A compares a sample of the B+ leg to a reference voltage. When
the B+ sample exceeds the reference voltage, the output of U23A will go OW. The OW
is routed to fault detector latch U21A/U21B. Open-loop conditions are monitored by
U23B. U23B compares a correction voltage sample to a reference voltage. When the
correction voltage sample exceeds the reference, the output of U23B will go OW. The
OW is inverted at U21D and applied to NAND gate U21C. With a HIGH power supply
enable signal from U12C, U21C will output a OW to fault detector latch U21A/U21B.
1-40. Over-current conditions are monitored by transistors Q19 and Q20. When an over-curĆ
rent condition occurs, Q19 and Q20 will output a OW. The OW is routed to fault detecĆ
tor latch U21A/U21B. Over-temperature conditions are monitored by temperature sensor
U25. When the power supply temperature exceeds 72 degrees C, U25 will output a OW
through transistor Q25 to U21D. The OW is inverted at U21D and applied to NAND
gate U21C.
1-41. With a OW from U21C or U23A, latch U21A/U21B will: 1) output a HIGH to transistor
Q16 and 2) output a OW to transistor Q15 and to U12B. Transistor Q16 will be biased
on and will output a OW to enable optical coupler U11. U11 will respond by generating
a power supply fault signal. AND gate U12B will output a OW to: 1) disable regulator
controller U13, 2) disable the SCR controlled rectifier circuit, and 3) initiate a logic seĆ
quence to enable the crowbar circuit (refer to the following text). Transistor Q15 will be
biased off and will disable optical coupler U10. The output of U10 will open.
1-42. The output of U10 is connected in parallel with U10 on each power supply circuit board.
When the output of U10 on each power supply circuit board is open, a HIGH power sup-
ply emergency signal to be applied to the controller. The power supply emergency signal
indicates all power supply modules contain fault conditions.
1-43. CROWBAR CIRCUIT.
1-44. The power supply circuit board is equipped with a crowbar circuit to discharge the B supĆ
ply during power supply off, ac off, and power supply mute conditions. The crowbar cir-
cuit consists of: 1) crowbar MOSFET Q23 and 2) resistor R72. Control of the circuit is
provided by logic gates which monitor power supply off, ac off, and power supply mute
conditions.
1-45. During a power supply off, ac off, or power supply mute condition, AND gate U12A will
output a OW to U12B. With a HIGH from U21A/U21B, U12B will output a OW to
transistor Q12. The OW biases Q12 and optical coupler U15 off. As a result, a HIGH is
applied to the gate of crowbar MOSFET Q23. The HIGH biases Q23 on to short the B
supply and discharge capacitors C24, C25, C26, C27 and C55. Resistor R72 limits the curĆ
rent during shorting operations.
1-46. When U15 is biased off, optical coupler U14 will also be disabled. With U14 disabled, a
OW is applied to U12C. U12C will output a OW to disable the PWM drive to the
switching regulator circuit.
1-8
1-47. POWER SUPPLY CIRCUIT GROUNDS.
1-48. The power supply circuit board is equipped with three isolated circuit grounds: 1) 0VS,
2) 0VP, and 3) 0VI. The circuit grounds are at different potentials and are not referenced
to earth ground. The 0VS ground is the circuit ground for the: 1) SCR controlled bridge
rectifier circuit, 2) soft-start control circuit, 3) ac line voltage detector circuit, and 4) low-
voltage detection circuit. The 0VP circuit ground is used to create the negative leg of the
B supply. The 0VI ground is the circuit ground for the: 1) crowbar circuit, 2) switching
regulator circuit, 3) inverting drive buffers, and 4) switching regulator transistors. The
circuit grounds are used in association with the circuitry to generate the operating volt-
ages for the RF power modules.
2-1
WARNING: DISCONNECT POWER PRIOR TO SERVICING
SECTION II
POWER SUPPLY CIRCUIT BOARD MAINTENANCE
2-1. INTRODUCTION.
2-2. This section provides maintenance information for the AM-10A/AM-6A transmitter
power supply circuit board assembly.
2-3. SAFETY CONSIDERATIONS.
WARNING
WARNING
WARNING
WARNING
THE TRANSMITTER CONTAINS MULTIPLE CIRCUIT
GROUNDS WITH HIGH AC AND DC POTENTIALS
WITH RESPECT TO THE CABINET WHICH IS AT
EARTH POTENTIAL. DO NOT ENERGIZE THE
TRANSMITTER WITH TEST EQUIPMENT CONĆ
NECTED TO THE TRANSMITTER OUTPUT
NETWORK, RF POWER MODULE, RF COMBINER, OR
POWER SUPPLY COMPONENTS.
2-4. The AM-10A/AM-6A transmitters contain high voltages and currents. If safety
precautions are not practiced, contact with the high voltages and currents could cause
serious injury or death. The transmitter is equipped with many built-in safety features,
however good judgement, care, and common sense must be practiced to prevent accidents.
2-5. In addition to high voltages and currents, the transmitters contain multiple circuit
grounds with high ac and dc potentials with respect to the cabinet which is at earth
potential. The potentials could cause serious injury or death if maintenance personnel
simultaneously touch a circuit ground and the cabinet. As a result, operation of the
transmitter with test equipment connected to transmitter output network, RF power
module, RF combiner, or power supply components is extremely dangerous and must not
be attempted. Therefore, never energize the transmitter with test equipment connected
to the transmitter output network, RF power module, RF combiner, or power supply
components. Test equipment may be connected to the ECU circuit boards from the front
of the transmitter using the supplied extender circuit board with power energized. The
maintenance procedures presented in this section should be performed only by trained
and experienced maintenance personnel.
2-6. FIRST LEVEL MAINTENANCE.
2-7. First level maintenance consists of precautionary procedures applied to the equipment to
prevent future failures. The procedures are performed on a regular basis and the results
recorded in a performance log.
2-8. CLEANING AND INSPECTION.
2-2
WARNING: DISCONNECT POWER PRIOR TO SERVICING
WARNING
WARNING
DISCONNECT ALL TRANSMITTER PRIMARY POWER
BEFORE PROCEEDING.
2-9. Ensure all transmitter primary power is disconnected and clean a circuit board of
accumulated dust as required using a nylon bristle brush and vacuum cleaner. Inspect
the circuit board for improperly seated semiconductors and components damage by
overheating. In addition, inspect the circuit board for loose hardware. Repeat the
procedure for each power supply circuit board in the transmitter.
2-10. SECOND LEVEL MAINTENANCE.
2-11. Second level maintenance is the performance of procedures required to restore a power
supply circuit board to operation after a fault has occurred. The power supply circuit
board contains no adjustments. Therefore, the following text presents only
troubleshooting procedures.
2-12. TROUBLESHOOTING.
WARNING
WARNING
WARNING
WARNING
THE TRANSMITTER CONTAINS MULTIPLE CIRCUIT
GROUNDS WITH HIGH AC AND DC POTENTIALS
WITH RESPECT TO THE CABINET WHICH IS AT
EARTH POTENTIAL. DO NOT ENERGIZE THE
TRANSMITTER WITH TEST EQUIPMENT CONĆ
NECTED TO THE TRANSMITTER OUTPUT
NETWORK, RF POWER MODULE, RF COMBINER, OR
POWER SUPPLY COMPONENTS.
2-13. SAFETY CONSIDERATIONS. The AM-10A/AM-6A transmitters are equipped with
extensive indicator and meter circuitry to allow the operator to isolate problems to a
specific area within the transmitter. Due to the hazardous voltages and currents
contained in the equipment, operation of the transmitter with test equipment connected
to transmitter output network, RF power module, RF combiner, or power supply
components is extremely dangerous and must not be attempted. Test equipment may be
connected to the ECU circuit boards from the front of the transmitter using the supplied
extender circuit board with power energized. The maintenance procedures presented in
this section should be performed only by trained and experienced maintenance personnel.
2-14. REMOVING/INSTALLING A POWER SUPPLY CIRCUIT BOARD. A power supply circuit
board is removed by disconnecting three connectors, loosening the mounting hardware,
and sliding the circuit board from the mounting pins. To remove or install a power supply
circuit board, proceed as follows:
WARNING
WARNING
DISCONNECT ALL TRANSMITTER PRIMARY POWER
BEFORE PROCEEDING.
2-15. Disconnect all transmitter primary power.
2-16. To remove a power supply circuit board, proceed as follows:
1. Refer to Figure 5-2/5-3 in SECTION V, MAINTENANCE and locate the desired
power supply circuit board to be removed.
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