Amplifier Research 75A250A Manual

Self-contained, broadband radio frequency (rf) amplifier

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SECTION I:
1.1
1.2
1.3
SECTION II:
2.1
2.2
2.2.1
2.2.2
SECTION III:
OPERATION
3.1
3.2
3.3
3.4
3.5
SECTION IV:
4.1
4.2
4.3
4.3.1
4.3.2
4.3.3
4.3.4
4.3.5
4.3.6
SECTION V:
5.1
5.2
5.3

TABLE OF CONTENTS

General Description ..................................................................1-1
Power Supplies.........................................................................1-1
Specifications ...........................................................................1-1
General............................................................................2-1
Amplifier Operation ..........................................................2-2
Local Operation........................................................................2-3
Remote Operation.....................................................................2-3
................................................................................................THEORY OF
Introduction ..............................................................................3-1
Amplifier Section ......................................................................3-1
Power Supply ...........................................................................3-2
Operate/Control Board..............................................................3-2
A3 Gain Control........................................................................3-2
General Maintenance Information ..............................................4-1
Disassembly Procedures ...................................................4-1
Troubleshooting ........................................................................4-2
Unit Cannot be Operated Remotely............................................4-3
Thermal Fault ...........................................................................4-3
Interlock Fault ..........................................................................4-3
Voltage/Amplifier Faults............................................................4-4
Low or No Power Output (DC Tests)........................................4-5
REPLACEABLE PARTS
Introduction ..............................................................................5-1
Ordering Information.................................................................5-1
Non-Listed Parts ......................................................................5-1
TABLE OF CONTENTS (
) iii
CONTINUED

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Summary of Contents for Amplifier Research 75A250A

  • Page 1: Table Of Contents

    TABLE OF CONTENTS SECTION I: GENERAL INFORMATION General Description ..............1-1 Power Supplies.................1-1 Specifications ................1-1 SECTION II: OPERATING INSTRUCTIONS General................2-1 Amplifier Operation ............2-2 2.2.1 Local Operation................2-3 2.2.2 Remote Operation..............2-3 SECTION III: ....................THEORY OF OPERATION Introduction ................3-1 Amplifier Section ..............3-1 Power Supply ................3-2 Operate/Control Board..............3-2 A3 Gain Control................3-2 SECTION IV:...
  • Page 2 Level of Maintenance ...............6-1 ARRANTIES IMITATION OF IABILITIES LIST OF FIGURES Model 75A250A Front Panel............ 2-2 Model 75A250A Rear Panel............. 2-2 LIST OF TABLES IEEE-488 Device Address Selection ......... 2-5 Remote Error Codes/Messages ..........2-6 RS-232 Connector Pin-Outs ............. 2-7...
  • Page 3: General Information

    90–132 Volts Alternating Current (VAC) and 180–264 VAC, 50/60Hz, universal or automatically selected. The user does not have to switch or change anything on the Model 75A250A when changing the unit’s AC input voltage. The unit’s AC power consumption is 400 watts nominal. A built-in circuit breaker provides primary AC circuit protection.
  • Page 4: Operating Instructions

    THIS NATURE WILL NOT BE COVERED UNDER THE UNIT S WARRANTY The Model 75A250A Amplifier is protected from input overdrive by a diode limiter on the RF input. The Model 75A250A power transistors are protected from over-temperature by a sensor that senses the heat sink temperature near the RF output transistors.
  • Page 5: Amplifier Operation

    Model 75A250A Manual Text MPLIFIER PERATION Figure 2-1 shows the front panel of the Model 75A250A broadband RF amplifier. Figure 2-1 Model 75A250A Front Panel Figure 2-2 shows the rear panel of the Model 75A250A broadband RF amplifier. Figure 2-2...
  • Page 6: Local Operation

    2.2.2 Remote Operation 2.2.2.1 Introduction This subsection describes remote operation of the Model 75A250A amplifier by utilizing either the IEEE-488 parallel interface or the RS-232 serial interface and a controlling devic e, such as a bus controller or a personal computer (PC).
  • Page 7: Ieee-488 Device Address Selection

    (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 Model 75A250A.) 2.2.2.4.1 RS-232 BAUD rate selection The serial communication (BAUD) rate can be set to five different levels.
  • Page 8 “Service Request” (SRQ) line is asserted; the operator can then perform a serial poll operation. The Model 75A250A error code (in binary) is contained in the returned serial poll status byte (STB). These error codes are defined in Table 2-2.
  • Page 9: Remote Error Codes/Messages

    Model 75A250A. The CTS line can be used as a “handshake” line to inform the Model 75A250A 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.
  • Page 10: Rs-232 Connector Pin-Outs

    2.2.2.8 Remote Commands The following commands are available to the user for remote communication and operation of the Model 75A250A. In the descriptions of these commands, a lower-case “x” is used to signify a numeric value or parameter. REV A...
  • Page 11 Manual Text 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 Model 75A250A. Syntax: Px Parameters: 0 = power off 1 = power on Example: To turn the power on, send the following command: P1<LF>...
  • Page 12: Introduction

    Manual Text INTRODUCTION The Model 75A250A amplifier consists of two (2) modules. The first module (A1) consists of three (3) cascaded mosfet amplifier stages that provide approximately 33dB of gain. This module drives the second module (A2) which consists of a dual mosfet amplifier operated as a push-pull stage that provides approximately 16dB of gain.
  • Page 13: A3 Gain Control

    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 75A250A via either remote bus. Besides being reported remotely, all amplifier faults are continuously monitored and indicated via the unit’s front panel VFD.
  • Page 14: Maintenance

    MAINTENANCE GENERAL MAINTENANCE INFORMATION The Model 75A250A 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.
  • Page 15: Troubleshooting

    OF ± ± 20 VOLTS, THIS WILL RESULT IN TRANSISTOR GAT FAILURE. Troubleshooting Troubleshooting the Model 75A250A 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.
  • Page 16: Unit Cannot Be Operated Remotely

    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...
  • Page 17: Thermal Fault

    Model 75A250A Manual Text 4.3.3 Thermal Fault (Schematic Diagram No 1011806) During a Thermal Fault, the front panel VFD should read “THERMAL FAULT.” REV A...
  • Page 18: Interlock Fault

    4.3.4 Interlock Fault (Schematic Diagram No. 1011806) The Model 75A250A 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.
  • Page 19: Voltage/Amplifier Faults

    Model 75A250A Manual Text 4.3.5 Voltage/Amplifier Faults (Schematic Diagram Nos. 1011806) The model 75A250A fault circuits sense voltage faults from PS1 (28V). They also sense an over current fault in the final amplifier stage. 4.3.5.1 Power Supply Faults (Schematic Diagram 1011806). PS1 sends a BUSS OK signal to the operate/control board (A4).
  • Page 20 Model 75A250A Manual Text REV -...

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