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Warranty Statement ... I-V 1 Preface Introduction ... 1-2 Design Innovations ... 1-2 New fast SCPI Bus ... 1-4 Rubidium Counter ... 1-4 2 Safety Instructions Introduction ... 2-2 Safety precautions ... 2-2 3 Preparation for Use Unpacking ... 3-2 Installation ... 3-2 4 Using the Controls About This Chapter ... 4-2 The User Interface ... 4-2 Default Settings ... 4-3 Basic controls ... 4-4 Input A controls ... 4-5 Measurement control keys ... 4-6 Display controls ... 4-7 ... 4-7 Display ... 4-8 Display ... 4-9 Rear Panel ... 4-10 Rear Panel ... 4-11 PM6685R Front Pane! ... 4-12 5 input Signal Conditioning Introduction to this chapter ... 5-2 Input A ... 5-2 Input C ... 5-6 Reducing Noise and Interference ... 5-6 6 Measuring Functions introduction to this chapter ... 6-2 Selecting function ... 6-2 Frequency ... 6-3 Introduction ... 6-3 Burst Frequency and PRF ... 6-6 AM Signals ... 6-10 Period ... 6-12 Introduction ... 6-12 Pulse Width and Duty Factor ... 6-13 Introduction ... 6-13 Pulse Width A ... 6-14 Duty Factor ... 6-14 Totalize ... 6-15 TOTalize A ... 6-15 7 Measurement Control About this chapter ... 7-2 Measuring Time ... 7-2 Display Hold ... 7-3 Arming ... 7-3 Digit Blanking ... 7-5 Controlling Measurement Timing . 7-6 Arming Set Up Time ... 7-12 Arming Examples ... 7*13 Example #1: ... 7-13 Example #2 ... 7-16 Example #3 ... 7-17 8 Processing Introduction ... 8-2 Averaging ... 8-2 Nulling ... 8-2 9 Auxiliary Functions About this chapter ... 9-2 Auxiliary Menu ... 9-2 10 Performance Check General Information ... 10-2 Recommended Test Equipment ... 10-2 Front Panel Controls ... 10-3 Short Form Specification Test ... 10-5 Rear Input/Output ... 10-6 Measuring Functions ... 10-7 PM9621, PM9624 and PM9625/25B____10-8 11 Preventive Maintenance Calibration and adjustment ... 11-2 Other Maintenance ... 11-4 12 Specifications Measuring Functions ... 12-2 Input and Output Specifications ... 12-3 Auxiliary Functions ... 12-4 GPiB (PM 9626B) ... 12-5 Measurement Uncertainties.12-6 Time Base Options ... 12-7 General Specifications ... 12-8 Ordering information ... 12-8 13 Appendix Appendix 1, Error Messages ... ,13-2 14 Index INDEX ... 14-11 15 Service Centers Saies and Service office ... 15-11

This is a complementary service manual covering instruments with manufacturing numbers exceeding 840684. The principal differences are to be found in Chapter 7 and in Chapter 8 due to a major redesign of the main PCB. Do not dispose of the previous edition, identified by the part number, 4822 872 25012, and the publishing date, June 1996. You may have to refer to it for information on older instruments as well as options not mentioned here. 1 Safety Instructions 2 Performance Check General Information ... 2-2 Recommended Test Equipment ... 2-2 Front Panel Controls ... 2-2 Short Form Specification Test ... 2-3 Rear Input/Output ... 2-4 Measuring Functions ... 2-4 Options ... 2-5 3 Disassembly Removing the Cover ... 3-2 Reinstalling the Cover ... 3-2 PM9624 (HF Input) ... 3-2 PM9626B (GPIB Interface) ... 3-3 PM9691 or PM9692 (Oven Oscillator) ... 3-3 4 Circuit Descriptions Block Diagram Description ... 4-2 General ... 4-2 Hardware Functional Description ... 4-4 Front Unit ... 4-4 Main Board ... 4-5 Rear Panel Unit ... 4-13 Optional Units ... 4-14 Software Functional Description ... 4-15 Test Routines ... 4-16 5 Repair Preventive Maintenance ... 5-2 Calibration ... 5-2 When to Replace the Fan (PM6685R only ) ... 5-3 Troubleshooting ... 5-4 General ... 5-4 Safety Inspection and Test After Repair ... 5-9 General Directives ... 5-9 6 Calibration Adjustments Introduction ... 6-2 Preparation ... 6-2 Power supply ... 6-2 Input Amplifier ... 6-3 Reference Oscillators ... 6-4 Other Options ... 6-6 7 Replacement Parts Introduction ... 7-2 Mechanical Parts ... 7-3 Main Board ... 7-6 Front Board ... 7-12 GPIB Interface (PM9626B) ... 7-13 8 Drawings & Diagrams How to read the diagrams ... 8-2 9 Appendix How to Replace Surface Mounted Devices ... 9-2 Electrostatic discharge ... 9-3 Glossary ... 9-4 Power supply Switchmode Module ... 9-5 Circuit Descriptions ... 9-5 Repair ... 9-6 Calibration Adjustments ... 9-7 Replacement Parts ... 9-8 PM6685R ... 9-12 Introduction ... 9-12 Performance Check ... 9-12 Functional Description ... 9-12 Calibration Adjustments ... 9-13 Replacement Parts ... 9-14

Programming Manual You should use this ProgrammingManual together with thePM6680B/1/5 Operators Manual. That manual contains specificationsfor the Counter and explanations of the possibilities and limitations of the different measuring functions. Sections The chapters in this manual are di- vided into three sections aimed at dif- ferent levels of reader knowledge. The ‘General’ Section, which can be disregarded by the users who know the IEEE-488 and SCPI standards: – Chapter 2 Bus Commands for the Benchtop User gives bus com- mands for the front panel keys. – Chapter 3 Introduction to SCPI explains syntax data formats, sta- tus reporting, etc. The Practical Section of this manualcontains: – Chapter 4, Programming Exam- ples, with examples of typical pro- grams for a wide variety of appli- cations. These programs are writ- ten in GW-basic and C. This Manual The ‘Programmers Reference’ Sec- tion of this manual contains: – Chapter 5, Instrument Model ex- plains how the instrument looks from the bus. This instrument is not quite the same as the one used from the front panel. – Chapter 6 Using the Subsystems explains more about each subsys- tem. – Chapter 7, How to Measure Fast is a set of measuring situations which the user is often confronted with when programming a Counter. This chapter also contains infor- mation about how to use the more complex subsystem. – Chapter 8, Error Messages con- tains a list of all error messages that can be generated during bus control. – Chapter 9, Command Reference, This chapter gives complete infor- mation on all commands. The sub- systems and commands are sorted alphabetically.