AR 150A400 User manual

Model 150A400 Manual Text
TABLE OF CONTENTS
SECTION I: GENERAL INFORMATION
1.1 General Description ..................................................................1-1
1.2 Power Supplies.........................................................................1-1
1.3 Specifications ...........................................................................1-1
SECTION II: OPERATING INSTRUCTIONS
2.1 General............................................................................2-1
2.2 Amplifier Operation ..........................................................2-2
2.2.1 Local Operation........................................................................2-2
2.2.2 Remote Operation.....................................................................2-2
SECTION III: THEORY OF OPERATION
3.1 Introduction..............................................................................3-1
3.2 Driver Amplifier Section............................................................3-1
3.3 Final Amplifier Section..............................................................3-1
3.4 Power Supply ...........................................................................3-2
3.5 Fault Board..............................................................................3-2
3.6 A3 Gain Control........................................................................3-2
SECTION IV: MAINTENANCE
4.1 General Maintenance Information..............................................4-1
4.2 Disassembly Procedures ...................................................4-1
4.3 Troubleshooting ........................................................................4-2
4.3.1 Front Panel Vacuum Fluorescent Display (VFD) Doesn’t Indicate
“PowerOn” ...........................................................................4-2
4.3.2 Unit Cannot be Operated Remotely............................................4-3
4.3.3 Thermal Fault ...........................................................................4-3
4.3.4 Interlock Fault ..........................................................................4-4
4.3.5 Voltage/Amplifier Faults............................................................4-4
4.3.6 Low or No Power Output (DC Tests)........................................4-5
SECTION V: REPLACEABLE PARTS
5.1 Introduction..............................................................................5-1
5.2 Ordering Information.................................................................5-1
5.3 Non-Listed Parts ......................................................................5-1
TABLE OF CONTENTS (CONTINUED)iii

Model 150A400 Manual Text
SECTION V: REPLACEABLE PARTS (CONTINUED)
5.4 Circuit Designators ...........................................................................................5-1
5.5 Manufacturers’ Abbreviation Listing..........................................5-2
5.6 Master List...............................................................................5-3
5.7 Schematics and Bills of Material (BOMs)...................................5-3
APPENDIX A: STANDARD ABBREVIATIONS FOR MANUFACTURERS ....................A-1
SECTION VI: RECOMMENDED SPARE PARTS
6.1 Level of Maintenance ...............................................................6-1
WARRANTIES: LIMITATION OF LIABILITIES
LIST OF FIGURES
2-1Model150A400 Front Panel..................................................... 2-2
2-2Model150A400 Rear Panel...................................................... 2-2
LIST OF TABLES
2-1IEEE-488 Device Address Selection......................................... 2-5
2-2Remote Error Codes/Messages ................................................ 2-6
2-3RS-232 Connector Pin-Outs ..................................................... 2-7

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SECTION I
GENERAL INFORMATION
1.1 GENERAL DESCRIPTION
The Amplifier Research (AR) Model150A400 is a self-contained, broadband Radio Frequency (RF)
amplifier designed for laboratory applications where instantaneous bandwidth, high gain, and moderate
power output are required. Solid state technology is used exclusively to offer significant advantages in
reliability and cost. When used with a frequency-swept signal source, the AR Model150A400 will
provide 150 watts of swept power output from .10 to 400 megahertz (MHz). Typical applications include
antenna and component testing, wattmeter calibration, electromagnetic interference (EMI) susceptibility
testing, use as a driver for frequency multipliers and higher power amplifiers, and use as an RF energy
source for Magnetic Resonance Imaging (MRI) studies. The Model150A400 can be operated locally by
using the unit’s front panel controls, or remotely by using its built-in IEEE-488 or RS-232 interfaces.
1.2 POWER SUPPLIES
The 150A400 contains four switching power supplies. The input voltage range to these supplies is 90-132
VAC and 180-264 VAC, 50/60 Hz universal or selected automatically. The operator does not have to
switch or change anything on the 150A400 when changing the AC input voltage. The power consumption
is a nominal 800 watts. A primary circuit breaker is provided. The output stage is protected by over
current sensing and over temperature sensing circuits which shut down the power supplies under fault
conditions.
1.3 SPECIFICATIONS
Refer to the Amplifier Research Data Sheet on the next page for detailed specifications.

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SECTION II
OPERATING INSTRUCTIONS
2.1 GENERAL
Operation of the Model150A400 broadband RF amplifier is simple. The input signal, whether swept or
fixed in frequency, is fed into the jack marked “INPUT”, and the amplifier’s output signal is taken from
the jack labeled “OUTPUT”.The unit is turned on by activating the power switch marked “POWER”. In
the event of a unit malfunction, protection is provided by an internal circuit breaker. A polarized, three (3)
wire AC power cord is also included with the unit to provide cabinet and chassis grounding to the power
mains.
CAUTION:
THE 150A400 AMPLIFIER IS NOT CRITICAL IN REGARDS TO SOURCE AND LOAD VSWR
AND WILL REMAIN UNCONDITIONALLY STABLE WITH ANY MAGNITUDE AND PHASE OF
SOURCE AND LOAD VSWR. IT ALSO HAS BEEN DESIGNED TO WITHSTAND, WITHOUT
DAMAGE, RF INPUT POWER UP TO TWENTY (20) TIMES ITS RATED INPUT OF 1mW.
HOWEVER, SIGNAL LEVELS HIGHER THAN 20mW OR TRANSIENTS WITH HIGH PEAK
VOLTAGES CAN DAMAGE THE AMPLIFIER. ALSO, ACCIDENTAL CONNECTION OF THE
OUTPUT TO ITS INPUT CAUSES OSCILLATIONS WHICH WILL PERMANENTLY DAMAGE
THE INPUT TRANSISTORS.
WHILE THE MODEL 150A400 WILL OPERATE INTO ANY LOAD IMPEDANCE, THE
AMPLIFIER MAY DRAW EXCESSIVE CURRENT AND SHUT DOWN IF IT IS
SIMULTANEOUSLY OVERDRIVEN WITH AN OPEN OR SHORT CIRCUITED LOAD. TO
AVOID TRIPPING THE PROTECTION CIRCUIT, THE FOLLOWING PRACTICES ARE
RECOMMENDED:
1. DO NOT INTENTIONALLY OVERDRIVE THE AMPLIFIER AT ANY TIME. WHEN
OPERATING INTO A MISMATCHED LOAD, TAKE SPECIAL PRECAUTIONS SO THAT
THE INPUT CANNOT BE INADVERTENTLY OVERDRIVEN.
2. WHEN CONNECTING AND DISCONNECTING CABLES, TURN THE POWER SWITCH
OFF. CARE MUST BE TAKEN TO PREVENT RESTRICTIONS OF THE COOLING FAN
AIR INLET OPENING ON THE UNIT. RESTRICTIONS OF THE OPENING, FOR
EXTENDED PERIODS, WILL CAUSE OVERHEATING OF THE UNIT AND POSSIBLE
PREMATURE FAILURE.

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2.2 AMPLIFIER OPERATION
Figure 2.1 shows the Model 150A400 in pictorial form.
FIGURE 2.1
AMPLIFIER OPERATION
2.2.1 Local Operation
Power-up Sequence:
1. Connect the input signal to the unit’s RF INPUT connector. The input signal level should be
0dBm maximum.
2. Connect the load to the unit’s RF OUTPUT connector.
3. Check to see that the MAIN POWER switch (circuit breaker) on the unit’s rear panel is set to
the 1(“on”) position.
4. Press the POWER switch: the front panel vacuum fluorescent display (VFD) should read
POWER ON, STATUS OK when power is applied.
(NOTE: The amplifier changes state each time the POWER switch is depressed—if the
unit is on when the POWER switch is depressed, it will turn off; if the unit is off when the
POWER switch is depressed, it will turn on.)
5. In the event of a fault, press the FAULT/RESET switch; if the fault does not clear, refer to
subsection 4.3 (“Troubleshooting”) of this manual.
6. Adjust gain control if necessary.
2.2.2.1 Introduction
This subsection describes remote operation of the Model150A400 amplifier by utilizing either the
IEEE-488 parallel interface or the RS-232 serial interface and a controlling device, such as a bus
controller or a personal computer (PC).

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2.2.2.2 Selecting Remote Operation
The Model 150A400 can be placed in the remote operation mode at any time by switching the
FUNCTION switch on the front panel to the REMOTE position. In this mode, control is
transferred to the selected remote interface and all front panel controls are inoperative with the
exception of the FUNCTION switch. The amplifier’s initial state will be Power Off. The front
panel VFD will indicate REMOTE until the unit is returned to the local operation mode.
2.2.2.3 Interface Selection
The Model150A400 can be controlled via either the IEEE-488 or RS-232 interface; which
interface is active is determined by the position of Switch 6 of the rear panel Dual In-Line
Package (DIP) switch located between the two interface connectors. If Switch 6 is in the “on”
(1) position, the RS-232 interface will be active; if Switch 6 is in the “off” (0) position, the
IEEE-488 interface will be active.
2.2.2.4 Interface Set-up
Switches 1–5 of the rear panel DIP switch are used to select either the RS-232 communication
(BAUD) rate or the IEEE-488 device address, depending upon which interface is active. (Note:
These switches are only read at device power-up. In order for changes made in these switch
settings to take place, AC power must be removed and then re-applied to the Model150A400.)
2.2.2.4.1 RS-232 BAUD rate selection
The serial communication (BAUD) rate can be set to five different levels. Selections are made
by the positions of Switches 1–5 of the rear panel DIP switch. The following is a list of the
available BAUD rates and the corresponding DIP switch positions:
BAUD Rate Switch On (1)
1200 1 only
2400 2 only
9600 3 only
19,600 4 only
76,800 5 only
(Note: Any other combination of switch settings will result in a BAUD rate equal to 1200.)
2.2.2.4.2 IEEE-488 device address selection
The IEEE-488 device address can be set to any number between 1 and 30. This selection is
made by setting Switches 1–5 of the rear panel DIP switch to the binary equivalent of the
number. Table 2-1illustrates this switch selection.

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2.2.2 Remote Operation (continued)
2.2.2.4.2 IEEE-488 device address selection (continued)
Table 2-1
IEEE-488 Device Address Selection
Device Address Switch 5Switch 4Switch 3Switch 2
Switch 1
1off (0) off (0) off (0) off (0) on (1)
2off (0) off (0) off (0) on (1) off (0)
3off (0) off (0) off (0) on (1) on (1)
4off (0) off (0) on (1) off (0) off (0)
5off (0) off (0) on (1) off (0) on (1)
:
:
30 on (1) on (1) on (1) on (1) off (0)
2.2.2.5 Command Set Format
Each command is composed of one alpha character, up to four numeric parameters, and a
command termination character. The command termination character is the “line feed”
command, which is denoted and entered as <LF>. Commands are case-sensitive and must be
entered in upper case only in order to be recognized.
2.2.2.6 IEEE-488 Communications
For IEEE-488 communications, the “End or Identify” (EOI) control line may also be used for
command termination. When sending commands to the Model150A400 via the IEEE-488 bus,
terminate each command with a <LF>, an EOI, or both. No characters are permitted after the
<LF> or EOI; the 150A400interprets characters following the <LF> or EOI as the start of the
next command. When an error condition is present at the Model150A400, the
“Service Request” (SRQ) line is asserted; the operator can then perform a serial poll operation.
The Model150A400 error code (in binary) is contained in the returned serial poll status byte
(STB). These error codes are defined in Table 2-2.

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2.2.2 Remote Operation (continued)
2.2.2.6 IEEE-488 Communications (continued)
Table 2-2
Remote Error Codes/Messages
IEEE-488 Serial Poll Model150A400 FAULT RS-232
Response (STB) Error
(binary/decimal) Message
(01000001) 65 BPM FAULT 1 E1
(01000010) 66 BPM FAULT 2 E2
(01000100) 68 THERMAL FAULT 1 E3
(01001000) 72 THERMAL FAULT 2 E4
(01010000) 80 INTERLOCK FAULT E5
(01100000) 96 PS1 FAULT E6
(01000000) 64 PS2 FAULT E7
(11000000) 192 PS4 FAULT E8
2.2.2.7 RS-232 Communications
If the RS-232 interface is active, the Model150A400 will test for a properly connected RS-232
interface when it is switched into the remote operation mode. In order for the Model150A400 to
recognize an RS-232 connection, the “Data Carrier Detect” (DCD) line must be asserted. This
line is sampled continuously to determine if the RS-232 connection is broken; therefore, it must
remain asserted in order for the RS-232 interface to function. The “Clear To Send” (CTS) line is
also used to gate information from the Model150A400. This line must be asserted in order to
receive information from the Model150A400. The CTS line can be used as a “handshake” line
to inform the Model150A400 when it is permissible to send information. If the CTS line is de-
asserted in the middle of a transmission, the character in the process of being transmitted will be
completed and further transmission will halt until the CTS line is re-asserted. The
Model150A400 itself asserts two lines: “Data TerminalReady” (DTR) and “Request To Send”
(RTS). The DTR line is continuously asserted, while the RTS line is used to gate information into
the Model150A400. Connector pin-out information is given in Table 2-3.

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2.2.2 Remote Operation (continued)
2.2.2.7 RS-232 Communications (continued)
Table 2-3
RS-232 Connector Pin-Outs
Pin No. Signal Data Direction* Description
1DCD <Device Carrier Detect
2RD <Receive Data
3TD >Transmit Data
4DTR >Data TerminalReady
5GND N/A Ground
6NC N/A No Connection
7RTS >Ready To Send
8CTS <Clear To Send
9NC N/A No Connection
*Note:
> = Output from Model150A400
< = Input to Model150A400
Special Note:A null modem cable or adapter is required in order to properly interface the
Model150A400 to a standard serial port on a computer.
Once the RS-232 interface is established, commands are processed in the same manner as that of
the IEEE-488 interface. The command structure is identical, except that there is no EOI line.
Therefore, all commands are terminated with a line feed (<LF>). Since this is a full-duplex
asynchronous interface, if the Model150A400 detects an error, the error message is immediately
transmitted to the host controller. These error messages are defined in Table 2-2.
2.2.2.7.1 RS-232 port settings
The RS-232 port settings used for communication with the Model150A400 are as follows.
Word Length: 8 bits
Stop Bits: 1
Baud Rate: 1200–76,800 (switch-selectable)
Parity: None
2.2.2.8 Remote Commands
The following commands are available to the user for remote communication and operation of the
Model150A400. In the descriptions of these commands, a lower-case “x” is used to signify a
numeric value or parameter.

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2.2.2 Remote Operation (continued)
2.2.2.8 Remote Commands (continued)
2.2.2.8.1 Power On/Off
Controls the power on/off state of the Model150A400.
Syntax: Px
Parameters: 0 = power off
1 = power on
Example: To turn the power on, send the following command:
P1<LF>
2.2.2.8.2 Gain Set
Sets the gain in steps of (Max Gain)/4096 W.
Syntax: Gxxxx
Parameters: 0000 = Minimum Gain
4095 = Maximum Gain
2.2.2.8.3 Reset
Resets the Model150A400, clearing all faults, if possible.
Syntax: R
Parameters: None
Example: To clear a fault, send the following command:
R<LF>

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SECTION III
THEORY OF OPERATION
3.1 INTRODUCTION
The Model 150A400 amplifier consists essentially of 2 push-pull output stages of broadband MOSFET transistors
driven by a driver amplifier. Overall power gain of the amplifier is a minimum of +52dB for 1 milliwatt input.
Input and output impedance matching circuits are utilized to provide optimum power transfer of the RF signal when
the amplifier is connected to source and load impedance of 50 ohms. Combined with negative feedback at each
stage and factory aligned equalizers, this provides an overall flat frequency response.
The self contained power supply consists of four switching power supplies. Two of the supplies are connected in
series to provide 33 volts for the final amplifier. The third supply provides 28 volts for the driver amplifier.The
fourth supply is used to supplies ±12VDC and +5VDC to power the operate/control and the gain control. The
four power supplies operate at line voltages of 90 to 132 VAC and 180 to 264 VAC, 50/60 Hz selected
automatically.
3.2 DRIVER AMPLIFIER SECTION
Refer to "Schematic Diagram Number 1010760, Driver Assy".
The input signal is fed through the gain control assy to the gate of Q1.Gate bias for Q1 is supplied through R5 and
adjusted by R4. The output of Q1 is coupled through C9 to the equalizing network R8, R9, R10, L5 and C11. The
output of the equalizing network is coupled through C12 to the gate of Q2. Gate bias for Q2 is supplied through
R12 and adjusted by R11.
The output of Q2 is coupled through transformersT1 and T4, which drives the push-pull stage Q4A and Q4B.
Resistor R20 is used to adjust the bias voltage for both Q4A and Q4B, in conjunction with R21 which is used to
balance the push-pull operation. The output of Q4A and Q4B are coupled through matching transformer T2 and
balun T3 to a coaxial connector, which is the driver's output.
3.3 TWO WAY SPLITTER
Refer to Schematic Diagram Number 1011336 Two Way Splitter
The output of the driver is fed to the two way splitter where the signal is evenly distributed to the two (separate)
Basic Power Modules.
3.4 FINAL AMPLIFIER SECTION
Refer to "Schematic Diagram Number 1011290, Basic Power Module (“A”)".
The following description applies to 1 section. The same description applies to the second Basic Power Module
“B”.
The input signal is applied to coax connector P2. The signal is then conducted to transformers T1 and T2 which
provide impedance matching to the push pull transistors Q1A and Q1B. The bias voltages are adjusted by R22 and
R23.

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The output of Q1A and Q1B are coupled through matching transformers T3 and T4 to the output connector P1.
Over current protection is provided by U1, U3, U4 and U5, by sensing the input current and lowering the bias
voltage if the current goes above the normal operating level.
3.5 TWO WAY COMBINER
The outputs of the two Basic Power Modules are fed to the two way combiner where the power is summed and then fed to the
main output of the amplifier.
3.6 POWER SUPPLY
Refer to "Schematic Diagram Number 1010877, Power Supply".
Input AC power is fed through RFI Filter FL1 before being switched by the circuit breaker CB1. The AC input
power is fed from CB1 to the four switching power supplies, PS1, PS2, PS3, PS4.
The four switching supplies work on line voltages of 90 to 132 VAC and 180 to 264 VAC 50/60 Hz. The input
voltage is selected automatically to conform to the supplied line voltage. No manual changes are required when
switching from one supply voltage to another.
The outputs of PS1 and PS2 are connected in series to supply 33 VDC to the Basic Power Modules (A & B)
amplifier circuits. The output of PS3 supplies ±12VDC and +5VDC to the operate/control circuits and the gain
control circuit. The fourth supply (PS4) supplies 28VDC to the driver amplifier.All the have current limited
outputs to protect them from shorts or over dissipation.
The 33VDC is fed through L1, which keeps switching transients from the supplies out of the amplifier circuits, to
the amplifier circuits.
If the currents in the output amplifiers get too high for the on board circuits to control, or if the heat sink
temperature gets too high, a fault signal is generated to shut down PS1 and PS2, and PS4.
3.7 A4 OPERATE/CONTROL BOARD (SCHEMATIC DIAGRAM No. 1008597)
The A4 Operate/Control Board is a microcontroller-based printed wiring board (PWB) assembly that allows
sensing and control of internal signals as well as remote personal computer (PC) control via on-board RS-232 and
IEEE-488 data communications ports. The A4 Operate/Control Board utilizes a state-of-the-art, Reduced
Instruction Set Computing (RISC) microcontroller that can quickly and reliably perform all front panel control and
monitoring tasks, thereby allowing real-time control to the Model 150A400 via either remote bus. Besides being
reported remotely, all amplifier faults are continuously monitored and indicated via the unit’s front panel VFD.
3.8 A3 GAIN CONTROL (SCHEMATIC DIAGRAM NO 1009914)
The gain control allows for gain adjustment either from the front panel or from the RS-232 Port or the IEEE-488
Port. U4 and U5 are 2 electronic attenuators connected in series to give a minimum adjustment range of 18 dB.
U1 is a switch that selects front panel control or remote control.

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SECTION IV
MAINTENANCE
4.1 GENERAL MAINTENANCE INFORMATION
The Model 150A400 should require very little maintenance, since it is a relatively simple instrument. It is built with
etched circuit wiring and solid state devices which should ensure long, trouble-free life. However, should trouble
occur, special care must be taken in servicing to avoid damage to the devices or the etched circuit board.
Since the components are soldered in place, substitution of components should be a last resort unless there is some
indication that they are faulty. In addition, take care when troubleshooting not to short voltages across the
amplifier. Small bias changes may ruin the amplifier due to excessive dissipation or transients.
Components within Amplifier Research instruments are conservatively operated to provide maximum instrument
reliability. In spite of this, parts within an instrument may fail. Usually, the instrument must be immediately
repaired with a minimum of "down time". A systematic approach can greatly simplify and thereby speed up the
repair.
However, due to the importance of the amplifier's alignment, it is recommended that when failure is caused by
breakdown of any of the components in the signal circuits, the amplifier be returned to the factory for part
replacement and amplifier realignment. Shipping instructions are as follows.
Ship: PREPAID
Via: UNITED PARCEL SERVICE
To: AMPLIFIER RESEARCH CORPORATION
160 SCHOOL HOUSE ROAD
SOUDERTON, PA 18964
See Warranty Statement at rear of panel.
4.2 DISASSEMBLY PROCEDURE
CAUTION:
REMOVE POWER CORD FROM RECEPTACLE BEFORE SERVICING.
4.2.1 Remove top cover by removing the screws.
4.2.2 Remove circuit board and heat sink by removing the screws around the perimeter of the heat sink.

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4.3 TROUBLESHOOTING
The techniques used in troubleshooting solid state instruments are similar to those used in vacuum tube
instruments. For instance, a good way to start troubleshooting is to check the supply voltage at the amplifier supply
voltage terminal. If it is low or nonexistent, check the power supply components.
The power supply for the driver should be a nominal 28 volts, and the power supply for the output stages should be
a nominal 33 volts. Incorrect voltage can result in over-dissipation in the transistors or severe distortion and non-
linearity of the amplifier. The power supplies may be disconnected from the RF board to enable troubleshooting
without danger of damaging the RF circuitry.
Finally, determine if the individual amplifier stages are operational by injecting a signal into the transistor gate and
looking for an indication of output.
CAUTION:
BEWARE OF VOLTAGES APPLIED TO THE GATE OF A MOSFET TRANSISTOR IN EXCESS
OF ±±20 VOLTS, THIS WILL RESULT IN TRANSISTOR GAT FAILURE.
4.3 Troubleshooting
Troubleshooting the Model150A400 in a logical manner can speed the solution to a problem. The settings
of potentiometers (“pots”), capacitors (“caps”), or other variables should not be disturbed until other
problems have been eliminated. Comparing the measured DC voltages to those shown on the schematics
can solve many problems. Before measuring circuit voltages, first verify that the voltages to the circuits
are correct.
Model150A400 Troubleshooting Categories:
Subsection 4.3.1—Front Panel Vacuum Fluorescent Display (VFD) Doesn’t Indicate “PowerOn”
when the POWER Switch is Depressed
Subsection 4.3.2—The Unit Cannot be Operated Remotely
Subsection 4.3.3—Thermal Fault
Subsection 4.3.4—Interlock Fault
Subsection 4.3.5—Voltage Faults
Subsection 4.3.6—Low or No Power Output (DC Tests)
4.3.1 Front Panel Vacuum Fluorescent Display (VFD) Doesn’t Indicate “PowerOn” when the
POWER Switch is Depressed (Schematic Diagram No. 1010877)
4.3.1.1 If the Model150A400 is operating in an otherwise normal fashion, the unit’s front panel
vacuum fluorescent display (VFD) or the wiring to it could be defective.

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4.3.1.2 Check the FUNCTION switch on the unit’s front panel; it must be set to the LOCAL
position in order to operate the front panel POWER switch. Check the circuit breaker on
the unit’s rear panel; it must be set to the “1” (“ON”) position.
4.3.1.3 4.3.1.3 If the “PowerOn” indication is not displayed and the cooling fan (Blower B1) is
not running, check to see that the unit is plugged into a live outlet and that the AC line
cord is plugged securely into the unit.
4.3.1.4 Check the output voltages from PS3; these voltages should be as follows:
PS3 J2, Pin 1 +12.0 ± 0.3VDC
PS3 J2, Pin 2 + 5.0 ± 0.2VDC
PS3 J2, Pin 6 -12.0 ± 0.3VDC
If output voltages are not present on PS3, check the AC input to PS3.
4.3.1.5 Check the voltages to the A4 Operate/Control Board on connector A4 J3; the voltages
should be as follows:
A4 J3, Pin 16 -12.0 ±0.3VDC
A4 J3, Pin 29 + 5.0 ±0.2VDC
A4 J3, Pin 31 +12.0 ±0.3VDC
4.3.1.6 Check the voltage on A4 J3, Pin 3; it should be ≥4V when the POWER switch (S1) is in
the normal position and <0.1V when S1 is depressed. S1 is normally open; it is closed only
when it is depressed. The amplifier should change state every time the POWER switch is
depressed.
4.3.1.7 If all voltages are correct and the unit still does not operate, contact Amplifier Research to
arrange for repair or replacement of the A4 Operate/Control Board.
4.3.2 The Unit Cannot be Operated Remotely
4.3.2.1 Verify that the front panel FUNCTION switch is set to the REMOTE position.
4.3.2.2 Verify that the unit operates locally by resetting the FUNCTION switch to the LOCAL
position; if the unit does not operate locally, see subsection 4.3.1 of this manual.
4.3.2.3 Check the position of the “ADDRESS” switch assembly (SW1) on the A4
Operate/Control Board; this assembly can be accessed through the unit’s rear panel. Check
to see that these switches are properly set for either RS-232 or IEEE-488 operation, as
desired.
(See subsection 2.2.2 of this manual for the proper “ADDRESS” switch settings.)
(Note: Address switches are only read at unit power-up; remove and re-apply AC power
(i.e., reset the circuit breaker) after changes are made.)

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4.3.3 Thermal Fault (Schematic Diagram No 1010877)
During a Thermal Fault, the front panel VFD should read “THERMAL FAULT.”

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4.3.3 Thermal Fault (Schematic Diagram No 1010877) (continued)
4.3.3.1 Try to reset the unit; if the unit resets and operates normally, check to see that the cooling
fan (B1) is operating normally and that the air inlet on the bottom of the unit and the air
outlets on the rear of the unit are not blocked.
4.3.3.2 If the unit does not reset and the cooling fan is operating normally, check the voltage at
the A4 Operate/Control Board, J3, Pins 42 and 43; it should be ≤0.1V.
4.3.3.3 If the voltage on A4 J3, Pin 21 is high, check the thermal daisy chain through A2AS1 and
A2BS1 to ground.
4.3.4 Interlock Fault (Schematic Diagram No. 1010877)
The Model150A400 is equipped with an interlock connector, which is located on the rear panel. The
interlock circuit can be used to sense the openings of doors to screen rooms, test chambers, and so forth,
and to turn off RF energy when these doors are opened.
Note: The Model150A400 is shipped with a mating connector, which has a jumper between
Pins 1 and 8, installed in the rear panel interlock connector. The unit will not operate unless
the interlock circuit is closed.
4.3.4.1 In the event of an Interlock Fault, the unit’s front panel VFD should indicate
“INTERLOCK FAULT.”
4.3.4.2 Check to see if it is safe to power up the unit—are there personnel present in the screen
room, or are doors to the screen room open?
4.3.4.3 After checking for safety, try to clear the Interlock Fault from the front panel by using the
RESET switch.
4.3.4.4 If the Interlock Fault will not clear, check for continuity in the External Interlock Circuit
(Pin 1 to Pin 8 in the connector, which mates with J2 in the rear panel).
4.3.4.5 Check the voltage on A4 J3, Pin 5; it should be ≤0.1V.
4.3.4.6 If all of the above voltages are correct and the unit still will not reset, check for defective
wiring and/or PWB connections, then try the RESET switch again. If the unit still will
not reset, the A4 Operate/Control Board is defective. Contact Amplifier Research to
arrange for repair or replacement of the A4 Operate/Control Board.

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4.3.5 Voltage/Amplifier Faults (Schematic Diagram Nos. 1010877)
The model 150A400 fault circuits sense voltage faults from PS1 (+15V) and PS2 (+15V) and PS4
(+28V). They also sense an over current fault in the final amplifier stage.
4.3.5.1 Power Supply Faults (Schematic Diagram 1010877). PS1 and PS2 send BUSS OK
signals to the operate/control board (A4). These signals give an early indication of over
voltage or over current conditions. If either condition occurs the power supplies send a
fault signal to the operate/control board which in turn sends a disable signal to the power
supplies turning off the outputs.
4.3.5.2 The Final Amplifier Assy Faults. (Schematic Diagram 1010877 and 1011290). The final
amplifier incorporates two stage protection for the output transistors. U1 monitors the
device current which is normally 8.0 amps. If the amplifier is over driven so that the
current rises to 9amps U1 will decrease the bias voltage thereby decreasing the current.
If the amplifier is over driven to the point that the active bias cannot control the current to
less than 10.0 amps U4 will generate a fault signal which will turn the power supplies off.
4.3.6 Low or No Power Output (DC Tests) (Schematic Diagram No. 1010877)
All indicators on the Model150A400 VFD are normal, the VFD indicates “POWER ON”and
“STATUS OK,” and the cooling fan (Blower B1) is operating.
4.3.6.1 Check the RF input to the unit—is it the correct amplitude and frequency?
4.3.6.2 Check the RF output connection from the unit—is it correctly connected to the load?
Is the coaxial cable okay?
4.3.6.3 Check the voltages at the following locations. Troubleshoot any incorrect voltages.
Feed-through Cap. Normal Voltage Remarks
A3 C9 +12V Gain Control
A3 C12 -12V Gain Control
A1 C1 +28V Driver Stage
A2 C1 +33V Final Amp
A2 C2 +33V Final Amp
A2C6 +33V Final Amp
A2C7 +33V Final Amp
Note:The locations of the feed-through capacitors can be found on the RF Assembly
Drawing and the Basic Wiring Diagram (Schematic Diagram No. 1010877).

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