Programmable Frequency Counter - Fluke

1 ProgrammableFrequencyCounterPM6685 & PM6685 RService Manual4822 872 20106 First Edition (May 2003)No part of this manual may be copied without the express permission of the copyright product names are trademarks of their respective companies. 2003 Pendulum Instruments ABAll rights reserved. Printed in is a complementary service manual covering instruments with manufacturing numbers exceeding 840684. The principaldifferences are to be found in Chapter 7 and in Chapter 8 due to a major redesign of the main not dispose of the previous edition, identified by the part number, 4822 872 25012, and the publishing date, June may have to refer to it for information on older instruments as well as options not mentioned Instructions2 Performance CheckGeneral Test Panel Form Specification the the (HF Input)..3-2PM9626B (GPIB Interface)..3-3PM9691 or PM9692 (Oven Oscillator)..3-34 Circuit DescriptionsBlock Diagram Functional Panel Functional to Replace the Fan(PM6685R only ).

2 Inspection and Test After Interface (PM9626B)..7-138 Drawings & DiagramsHow to read the to Replace Surface Mounted Supply Switchmode page is intentionally left 1 Safety InstructionsWARNING: These servicing instructions are for useby qualified personnel only. To reduce the risk ofelectric shock, do not perform any servicing otherthan that specified in the Operating Manual unlessyou are fully qualified to do service and calibration of this instrument is availablethrough your Fluke representative. See address at the end of this chapter carefully before you check, adjust, or repair an and Warning StatementsYou will find specific warning and caution statements where neces-sary throughout the : Indicates where incorrect operating proce-dures can cause damage to, or destruction of,equipment or other : Indicates a potential danger that requirescorrect procedures or practices in order to preventpersonal Timer/ Counter has been designed and tested in accordance withsafety class 1 requirements for Electronic Measuring Apparatus ofIEC (CENELEC) publication EN61010-1, and CSA 1010-1, and has been supplied in a safe manual contains information and warnings that should be fol-lowed by the user and the service technician to ensure safe operationand repair in order to keep the instrument in a safe.

3 Opening instrument covers or removingparts, except those to which access can be gainedby hand, is likely to expose high voltages whichcan cause instrument must be disconnected from all voltage sources beforeit is opened. Remember that the capacitors inside the instrument re-tain their charge even if the instrument has been disconnected fromall voltage instrument is connected to ground via a sealed three-core powercable, which must be plugged into socket outlets with protectiveground contacts. No other method of grounding is permitted for ground symbol on the rear panel indicates where theprotective ground lead is connected inside the remove or loosen this the instrument is brought from a cold to a warm environment,condensation may cause hazardous conditions. Therefore, ensurethat the grounding requirements are strictly extension cables must always have a protective ground that the operator should consult the : Any interruption of the protective groundconductor inside or outside the instrument, or dis-connection of the protec- tive ground terminal, islikely to make the instrument dangerous.

4 Do not in-tentionally disrupt the protective of Hazardous MaterialsWARNING: Disposal of lithium batteries requires spe-cial attention. Do not expose the batteries to heator put them under extensive pressure. These mea-sures may cause the batteries to lithium battery is used to power the nonvolatile RAM in this in-strument. Our world suffers from pollution, so don t throw batteriesinto your wastebasket. Return used batteries to your supplier or to theFluke representative in your VoltageThe instrument can be powered by any voltage between 90 and265 VACwithout range switching. This makes it suitable for all nom-inal line voltages between 100 and 240 Components in Primary CircuitsComponents that are important for the safety of this instrument mayonly be replaced by components obtained from your local Flukerepresentative. After exchange of the primary circuits, perform thesafety inspection and tests, as described in Chapter 5, Repair.

5 NFusesThis instrument is protected by an ordinary A slow blow fusemounted inside the instrument. NEVER replace this fuse withoutfirst examining the Power Supply Safety Instructions,Chapter 2 Performance CheckGeneral InformationWARNING: Before turning on the instrument, ensurethat it has been installed in accordance with the In-stallation Instructions outlined in Chapter 3 of theOperators performance procedure is intended to: Check the instrument s specification. Be used for incoming inspection to determine the acceptabilityof newly purchased instruments and recently recalibrated in-struments. Check the necessity of recalibration after the specifiedrecalibration : The procedure does not check every facet of the in-strument s calibration; rather, it is concerned primarilywith those parts of the instrument which are essentialfor determining the function of the is not necessary to remove the cover of the instrument to performthis the test is started less than 20 minutes after turning on the instru-ment, results may be out of specification, due to insufficientwarm-up TestEquipment*) Two of the cables must have 10 ns difference in delay, for ex-ample: 5 ns and 15 up your instruments at least 20 minutes be-fore beginning the tests to let them reach normaloperating temperature.

6 Failure to do so may resultin certain test steps not meeting equipment Panel ControlsPower-On TestAt power-on the Counter performs an automatic self-test of the fol-lowing: Microprocessor RAM ROM Measuring circuits DisplayIf a GPIB interface is installed, the GPIB address is there are any test failures, an error message is shown. Turn on the Counter and check that all segments light up on thedisplay and that no error message Self-TestsThe different built-in test routines invoked by the power-on test canalso be activated from the front panel as follows: Enter the Auxiliary Menu by pressingAUX MENU. Select the test submenu by pressingDATA ENTRYup ordown. Enter the test menu by pressing for internal self-tests are:1 TEST ALL (Test 2 to 5 in sequence)2 TEST RO (ROM)3 TEST RA (RAM)4 TEST LOGIC (Measuring Logic)5 TEST DISP (Display Test) UseDATA ENTRYup/down to select TEST ALL, then pressENTER.

7 If any fault is detected, an error message appears on the dis-play and the program halts. If no faults are detected, the program returns to Performance Check, General InformationType of instru-mentRequiredSpecificationsSuggest edEquipmentLF SynthesizerSquare;Sine up to 10 MHzPower Splitter50 WPM9584/02T-pieceTermination50 WPM9585 Reference oscilla-tor10 MHz Hz forstandard oscillatorFluke Counter withcalibrated optionPM969110 MHz Hz forPM9691 & PM9692 Fluke PM6685R orPM6681R10 MHz Hzfor PM6685 RFluke 910R or Ce-sium StandardHF signal GHz (no presc.) GHz (option 10)Pulse Generator125 MHzOscilloscope withprobes350 MHzBNC cables5 to 7 cables *Table 2-1 Recommended Test Equipment. Fig. 2-1 Text on the TestThe keyboard test verifies that the Counter responds when you pressany key. To check the function behind the keys, see the tests furtheron in this the keys as described in the left column and look on the displayfor the text, as described in the second column.

8 Some keys changemore text on the display than described here. The display text men-tioned here is the text mainly associated with the selected : For the instrument to respond correctly, this test mustbe carried out in sequence and you must start with thepreset (power-on) setting.* The LSD may vary.** MENU is not disabled by setting DEFAULT; press menu Form SpecificationTestSensitivity and Frequency Range Press thePRESETkey to set the Counter in the default confirm by pressingENTER. Turn off AUTO. Select IMP A = 50 Wand maximum sensitivity. Connect a signal from a HF generator to a BNC power splitter. Connect the power splitter to your Counter and an oscilloscope. Set input impedance to 50 Won the oscilloscope. Adjust the amplitude according to the following table. Readthe level on the oscilloscope. The Counter should display thecorrect OscillatorsX-tal oscillators are affected by a number of external conditions,such as ambient temperature and supply voltage, but they are also af-fected by aging.

9 Therefore, it is hard to give limits for the allowedfrequency deviation. You must decide the limits depending on yourapplication, and recalibrate the oscillator accordingly. See the Pre-ventive Maintenance in the Repair chapter, Chapter check the accuracy of the oscillator you must have a calibratedreference signal that is at least five times as stable as the oscillatorthat you are testing, see the following table. Press thePRESETkey, then press theENTERkey to set yourcounter in the Default Check, Short Form Specification Test 2-3 Key(s)DisplayNotePass/FailSTAND-BYDispla y OffRed LEDbesidethe keyOnONBacklight onPRESETENTERDEFAULT?NO SIGNALD efaultsettingEXT REFEXT REFI nput AFILTERFILTER50W50W(2 times)SENS (2 times)Bar graph:zzzzzzzzSENS (2 times)Bar graph:zzzzzzzzzzAUTOAUTO TRIGO therPRESETENTERDEFAULT?NO SIGNALD efaultsettingMEAS TIME200 3sDATA ENTRY 500 3sDATA ENTRY 200 3sENTERNO SIGNALDISPLAY HOLDHOLDDISPLAY HOLDSINGLESINGLEFUNCTION DUTY F AFUNCTION TOT A MANFUNCTION DUTY F AFUNCTION FREQ AAUX MENURECALLMEAS RESTARTNO SIGNALPRESETENTERDEFAULT?

10 NO * *BLANK DIGITS(3 times) *MENUD isplays all avail-able functions, pro-cesses and inputcontrols. Selecteditems are 2-2 Keyboard A13010 27253010 27503010 271506020 212009030 1725015050-1330015050-13 Table 2-3 Sensitivity of input A at various tempera-ture dependenceMax. agingper monthMax. agingper yearStandard 100 Hz 5 Hz 50 HzPM9691 Hz Hz HzPM9692 Hz Hz Hz Hz HzTable 2-4 Deviation (for PM9691 and PM9692 after awarm-up period of 48 hours). Connect the reference to input A. Check the readout against the accuracy requirements of TestAs an acceptance test, the following table gives a worst case figureafter a 30 minute warm up time. All deviations that can occur in ayear are added Test, PM6685 RTo fully test the accuracy of the PM6685R, a reference signal of ex-tremely high stability is needed. Examples of such references areCesium Atomic references, or transmitted signals from a nationallyor internationally traceable source, like the GPS Test EquipmentTypeStabilityModel10 MHz refer-ence 1x10-10910R with satellite contact dur-ing the last 72 Procedure Connect the Counter to the line power.