Fluke PM6690 User manual

Timer/Counter/
Analyzer
PM6690
Service Manual

II
4822 872 20306
May 2006 - Fourth Edition
© Fluke Corporation. All rights reserved.
Printed in Sweden.

GENERAL INFORMATION
Method of Notation
This manual contains directions and information that apply to the PM6690 Timer/Counter/Analyzer. In order to simplify the references,
the following designation system is used throughout the manual:
–PM6690 is abbreviated to '90'.
Warranty
The Warranty Statement is included in the Getting Started Manual.
Declaration of Conformity
The complete text with formal statements concerning product identification, manufacturer and standards used for type testing is avail-
able on request.
Hardware Versions
This Service Manual provides Source of Supply information for the Fluke Model PM6690 Timer/Counter/Analyzer, which may con-
tain an OLD version of the Main CCA, called Version A, or a NEW version of the Main CCA, called Version B. Both the old and the
new version of the Main CCA have the same part number. All orders for the old version of the Main CCA will be filled with the new ver-
sion of the Main CCA. When the old version of the Main CCA is returned to the factory for repair, the new version of the Main CCA
will be returned in place of the old version of the Main CCA, if the microprocessor has to be replaced.
Devices with serial numbers up to and including 916779 are equipped with a Triscend microprocessor, whereas devices with higher se-
rial numbers have a Sharp microprocessor. Both are based on an ARM7 core, and from the operator’s point of view the behavior is not
affected. However, essential parts of the main PCB differ, and the corresponding sections of the service manual are consequently af-
fected. Even though large parts of the hardware are common to both versions, we have preferred to divide the pertinent chapters into
separate sections, where certain parts are repeated, all in order to improve legibility and simplify troubleshooting.
Version A refers to devices equipped with the Triscend microprocessor.
Version B refers to devices equipped with the Sharp microprocessor.
The chapters that need special attention are:
Chapter 4, Circuit Descriptions
Chapter 6, Repair
Chapter 8, Replacement Parts
Chapter 9, Schematic Diagrams
nFirmware Compatibility
Despite the relatively large hardware differences, we have managed to integrate the firmware, so that future upgrades can be applied to
both versions by means of the same hex file. Thus there is no need to check the serial number or else find out which processor is inside
the cover. Just proceed according to the instructions given in Chapter 5, Corrective & Preventive Maintenance.
III

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IV

Contents
GENERAL INFORMATION.....................III
1 Safety Instructions
Caution and Warning Statements ...............1-2
Grounding ................................. 1-2
Operation ................................. 1-2
Line Voltage ............................... 1-4
2 Performance Check
General Information .........................2-2
Test Equipment............................. 2-2
Preparations ............................... 2-2
Front Panel Controls.........................2-2
Short Form Specification Test..................2-4
Rear Inputs/Outputs .........................2-6
Measuring Functions.........................2-6
Check of HOLD OFF Function .................2-7
RF Options ................................ 2-7
3 Disassembly
Removing the Cover .........................3-2
Fan...................................... 3-3
Prescaler Options ........................... 3-3
OCXO Options ............................. 3-4
4 Circuit Descriptions
Version A .................................. 4-3
Block Diagram Description ....................4-4
General ................................... 4-4
Block Diagram ............................. 4-4
Hardware Functional Description ...............4-6
Front Unit ................................. 4-6
Main Board ................................ 4-6
Test Routines ............................. 4-10
Version B ................................. 4-11
Block Diagram Description ...................4-12
General .................................. 4-12
Block Diagram.............................4-12
Hardware Functional Description ..............4-14
Front Unit ................................ 4-14
Main Board ............................... 4-14
Test Routines ............................. 4-18
5 Corrective & Preventive Maintenance
Introduction ................................ 5-2
Calibration................................. 5-2
Instructions for Firmware Upgrade ..............5-2
Utility Program .............................5-3
Fan Replacement ...........................5-3
Other Important Information ...................5-3
6 Repair
Version A .................................. 6-3
Troubleshooting.............................6-4
General ................................... 6-4
Power Supply .............................. 6-4
Input Amplifiers .............................6-8
Timebase Reference Circuits .................6-12
Prescalers................................ 6-15
Microprocessor & Memories ..................6-15
Microprocessor Bus & Interfaces ..............6-21
Measuring Logic ...........................6-27
Version B ................................. 6-31
Troubleshooting............................ 6-32
General .................................. 6-32
Power Supply ............................. 6-32
Input Amplifiers ............................6-36
Timebase Reference Circuits .................6-40
Prescaler................................. 6-43
Microprocessor & Memories ..................6-43
Microprocessor Bus & Interfaces ..............6-49
Measuring Logic ...........................6-55
Safety Inspection and Test After Repair.........6-59
General Directives .........................6-59
7 Calibration Adjustments
Calibration ................................. 7-2
General Principles...........................7-2
The Calibration Submenu .....................7-3
Frequency Reference ........................7-3
Voltage Reference ..........................7-5
Calibration Subsystem
Command Reference .........................7-6
Adjustments ............................... 7-11
Preparations .............................. 7-11
Input Amplifiers ............................7-12
Power Supply ............................. 7-13
V

External Reference Input ....................7-13
Internal Reference Oscillators.................7-14
RF Input 3 GHz............................7-14
8 Replacement Parts
Introduction ................................ 8-2
Mechanical Parts ...........................8-3
Main Board, Version A .......................8-5
Front Unit ................................ 8-14
Main Board, Version B ......................8-16
Parts Unique to Version A....................8-26
Parts Unique to Version B....................8-26
Parts Common to Version A and Version B ......8-26
9 Schematic Diagrams
How to Read the Diagrams....................9-2
Version A .................................. 9-3
Version B ................................. 9-25
10 Appendix
How to Replace Surface Mounted Devices.......10-2
Electrostatic Discharge ......................10-3
Glossary ................................. 10-3
11 Index
VI

Chapter 1
Safety Instructions

WARNING: These servicing instructions are
for use by qualified personnel only. To re-
duce the risk of electric shock, do not
perform any servicing other than that
specified in the Operators Manual unless
you are fully qualified to do so.
Caution and Warning
Statements
Introduction
Read this chapter carefully before you check, adjust or repair
the instrument.
It is essential for your own safety to know the restrictions that
are applicable to all equipment that can be connected to line
power. Therefore, read the section on Safety Precautions be-
low.
In addition to the general statements given in this chapter you
will find specific caution and warning statements where nec-
essary throughout the manual.
Safety Precautions
This instrument has been designed and tested for Measurement Cate-
gory I, Pollution Degree 2, in accordance with EN/IEC
61010-1:2001 and CAN/CSA-C22.2 No. 61010-1-04 (including ap-
proval). It has been supplied in a safe condition.
This manual contains information and instructions that should
be followed by the user and the service technician to ensure
safe operation and repair in order to keep the instrument in a
safe condition. It is essential that you follow generally ac-
cepted safety procedures in addition to the safety precautions
specified in this manual.
The instrument is designed to be used by trained personnel
only. Removing the cover for repair, maintenance, and adjust-
ment of the instrument must be done by qualified personnel
who are aware of the hazards involved.
The warranty commitments are rendered void if unautho-
rized access to the interior of the instrument has taken
place during the given warranty period.
CAUTION: Indicates where incorrect proce-
dures can cause damage to, or destruction
of equipment or other property.
WARNING: Indicates a potential danger that
requires correct procedures or practices
to prevent personal injury.
Symbols
Shows where the protective ground terminal is con-
nected inside the instrument. Never remove or
loosen this screw.
Indicates that the operator should consult the manual.
You can, for instance, find such a symbol on the front
panel below the A and B inputs. It points out that the
damage level for the input voltage decreases from 350 Vpto
12 Vrms when you switch the input impedance from 1 MWto
50 W.
If in Doubt about Safety
Whenever you suspect that it is unsafe to use the instrument,
you must make it inoperative by doing the following:
–Disconnecting the line cord
–Clearly marking the instrument to prevent its further op-
eration by unauthorized personnel
For example, the instrument is likely to be unsafe if it is visi-
bly damaged.
Grounding
Grounding faults in the line voltage supply will make any in-
strument connected to it dangerous. Before connecting any
unit to the power line, you must ensure that the protective
ground functions correctly. Only then can a unit be connected
to the power line and only by using a three-wire line cord. No
other method of grounding is permitted. Extension cords must
always have a protective ground conductor.
CAUTION: If a unit is moved from a cold to
a warm environment, condensation may
cause a shock hazard. Ensure, therefore,
that the grounding requirements are
strictly met.
WARNING: Never interrupt the grounding
cord. Any interruption of the protective
ground connection inside or outside the
instrument or disconnection of the protec-
tive ground terminal is likely to make the
instrument dangerous.
Operation
Orientation and Cooling
The instrument can be operated in any position desired. Make
sure that the air flow through the ventilation slots at the top,
1-2 Safety Instructions

and side panels is not obstructed. Leave 5 centimeters (2
inches) of space around the counter.
Fold-Down Support
For bench-top use, a fold-down support is available for use
underneath the counter. This support can also be used as a
handle to carry the instrument.
Rackmount Adapter
If you have ordered a 19-inch rack-mount kit for your instru-
ment, it has to be assembled after delivery of the instrument.
The rackmount kit consists of the following:
– 2 brackets, (short, left; long, right)
– 4 screws, M5 x 8
– 4 screws, M6 x 8
WARNING: Do not perform any internal ser-
vice or adjustment of this instrument
unless you are qualified to do so.
Before you remove the cover, disconnect
mains cord and wait for one minute.
Capacitors inside the instrument can hold
their charge even if the instrument has
been separated from all voltage sources.
nAssembling the Rackmount Kit
–Make sure the power cord is disconnected from the in-
strument.
–Turn the instrument upside down.
See Fig. 1-3.
–Undo the two screws (A) and remove them from the
cover.
–Remove the rear feet by undoing the two screws (B).
–Remove the four decorative plugs (C) that cover the
screw holes on the right and left side of the front panel.
–Grip the front panel and gently push at the rear.
–Pull the instrument out of the cover.
– Remove the four feet from the cover.
Use a screwdriver as shown in the following illustration or a
pair of pliers to remove the springs holding each foot, then
push out the feet.
–Push the instrument back into the cover. See Fig. 1-3.
–Mount the two rear feet with the screws (B) to the rear
panel.
–Put the two screws (A) back.
–Fasten the brackets at the left and right side with the
screws included as illustrated in Fig. 1-1.
–Fasten the instrument in the rack via screws in the four
rack-mounting holes
Safety Instructions 1-3
Fig. 1-1 Dimensions for rackmounting hardware.
Fig. 1-2 Fitting the rack mount brackets on the counter.
Fig. 1-3 Remove the screws and push the counter out of the
cover.
Fig. 1-4 Removing feet from the cover.

The long bracket has an opening so that cables for Input A, B,
and C can be routed inside the rack.
nReversing the Rackmount Kit
The instrument may also be mounted to the right in the rack.
To do so, first remove the plate on the long bracket and fasten
it on the short one, then perform the preceding steps.
Line Voltage
nSetting
The Counter may be connected to any AC supply with a volt-
ageratingof90to265V
rms, 45 to 440 Hz. The counter auto-
matically adjusts itself to the input line voltage.
nFuse
The secondary supply voltages are electronically protected
against overload or short circuit. The primary line voltage side
is protected by a fuse located on the power supply unit. The
fuse rating covers the full voltage range. Consequently there
is no need for the user to replace the fuse under any operating
conditions, nor is it accessible from the outside.
CAUTION: If this fuse is blown, it is likely
that the power supply is badly damaged.
Replace the complete power supply unit.
Do not replace the fuse.
1-4 Safety Instructions

Chapter 2
Performance Check

General Information
WARNING: Before turning on the instru-
ment, ensure that it has been installed in
accordance with the Installation Instruc-
tions outlined in Chapter 1 of the
Operators Manual.
This performance procedure is intended for:
–checking the instrument’s specification.
–incoming inspection to determine the acceptability of
newly purchased instruments and recently recalibrated
instruments.
–checking the necessity of recalibration after the specified
recalibration intervals.
NOTE: The procedure does not check every facet of the in-
strument’s calibration; rather, it is concerned primarily
with those parts of the instrument which are essential
for determining the function of the instrument.
It is not necessary to remove the instrument cover to perform
this procedure.
Test Equipment
Preparations
Power up your instrument at least 30 minutes
before checking to let it reach normal operating
temperature. Failure to do so may result in cer-
tain test steps not meeting equipment specifications.
Front Panel Controls
Internal Self-Tests
The test programs forming the self-diagnosis can be activated
from the front panel as follows:
–Press USER OPT
–Press Test.
–Press Test Mode.
–Select one of the six tests available by pressing the
softkey below the label with the name of the test func-
tion. Five of the tests (RAM, ROM, Logic, Display, and
Interface) are individual. They are briefly described be-
low. The sixth, named All, performs all five individual
tests in sequence.
•All - all tests performed in sequence
•RAM - test of RAM memory
•ROM - test of ROM memory
•Logic - test of counter ASIC and other logic circuits.
•Display - test of graphic display
module
•Interface - test of GPIB and USB
– Press Start Test.
– If a fault is detected, an error message appears on the
display and the program halts. Note any error messages.
– If no faults are detected, the instrument returns to the
normal measurement mode.
Keyboard Test
See Table 2-3. This test verifies that the timer/counter re-
sponds when you press any key. It is not a functional test.
Such tests are performed later in this chapter. The important
thing here is that something changes on the display when you
press a key. Consequently you can press the keys in almost
any order without paying attention to the exact response, but
for those who want to be more systematic there is a table over-
leaf, where all keys are exercised at least once.
Press the keys as described in the first column and look at the
display for the text in the second column. Some keys change
more text on the display than described here. The display text
mentioned here is the one mostly associated with the selected
key.
NOTE: For the instrument to respond correctly, this test
must be carried out in sequence and you must start
with the DEFAULT setting. Do as follows:
–Press USER OPT.
–Press Save/Recall.
–Press Recall Setup.
–Press Default.
See Table 2-2 for the complete list of default settings.
2-2 Performance Check, General Information
Type of Equipment Required Specifications
Reference Oscillator
10 MHz, 1*10–8 (e.g. 908) for calibrat-
ing PM6690/_1_
10 MHz, 1*10–9 (e.g. 909) for calibrat-
ing PM6690/_5_ & PM6690/_6_
Voltage Calibrator
DC -50 V to +50 V (e.g. 5500A) for
calibrating the built-in voltage refer-
ence, alternatively corresponding DC
power supply + DVM with uncertainty
<0.1 %
LF Synthesizer Square/ Sine up to 10 MHz, 10 VRMS
Pulse Generator 2 ns rise time, 5 V peak, >10 MHz,
continuous & one-shot trigger
Oscilloscope 350 MHz, <3% voltage uncertainty
RF Signal Generator 10 MHz to 3 or 8 GHz dep. on
prescaler option, 10 MHz ext.ref.
Power Splitter 50 W6dBBNC
T Adapter (F-M-F) BNC
Termination 50 Wfeedthrough BNC
Lowpass Filter 50 kHz (for 1 MWload)
BNC Cables 5 to 7 pcs of suitable lengths
Table 2-1 Recommended equipment for calibration and per-
formance check.

Performance Check, Front Panel Controls 2-3
PARAMETER VALUE/SETTING
Input A & B
Trigger Level AUTO
Trigger Slope POS
Impedance 1 MW
Attenuator 1x
Coupling AC
Filter OFF
Arming
Start OFF
Start Slope POS
Start Arm Delay 200 ms
Stop OFF
Stop Slope POS
Hold-Off
Hold-Off State OFF
Hold-Off Time 200 ms
Time-Out
Time-Out State OFF
Time-Out Time 100 ms
Statistics
Statistics OFF
No. of Samples 100
No.ofBins 20
Pacing State OFF
Pacing Time 20 ms
Mathematics
Mathematics OFF
Math Constants K=1, L=0, M=1
Limits
Limit State OFF
Limit Mode ABOVE
Lower Limit 0
Upper Limit 0
Burst
Sync Delay 200 ms
Start Delay 200 ms
Meas. Time 200 ms
Freq. Limit 300 MHz
Miscellaneous
Function FREQ A
Meas. Time 200 ms
Smart Time Interval OFF
Auto Trig Low Freq 100 Hz
Timebase Reference INT
Table 2-2 Default settings for functions and parameters.
KEY(S) DISPLAY NOTES P/F
STANDBY Off Red standby LED On
(KeycommontoON)
ON Backlight On Red standby LED Off
(Key common to
STANDBY)
INPUT A Input A: Menu for setting Slope,
Coupling, Impedance
etc.
Man Trig xx mV
Trig Trig: xx mV Menu for entering nu-
meric values
0.123V Trig: 0.123 V
t(5 times) Trig: _ V
4.567 Trig: 4.567 V
t(5 times) Trig: _ V
8.9 Trig: 8.9 V
± Trig: -8.9 V
mV Trig: -8.9 mV
V Trig: -8.9 V
AUTOSET Menu disappears
INPUT B Input B: Menu for setting Slope,
Coupling, Impedance
etc.
SETTINGS Settings: Menu for setting Meas
Time, Hold-Off, Ref.
Source etc.
ENTER Meas Time: 200 ms
pMeas Time: 500 ms
qMeas Time: 200 ms
EXIT/OK Settings: Menu for setting Meas
Time, Hold-Off, Ref.
Source etc.
EXIT/OK Menu disappears
MATH/LIM Math/Limit: Menu for selecting
post-processing for-
mula and alarm limit
USER OPT User options: Menu for Calibration,
Memory Management,
Interface etc.
CANCEL Menu disappears
HOLD/RUN Hold At upper right corner
HOLD/RUN Hold disappears
MEAS FUNC Measure function: Menu for selecting
measurement function
uPeriod Cursor position marked
by text inversion
ENTER Single A
EXIT/OK Menu disappears Period Single A: at up-
per left corner
STAT/PLOT Period Single A
MEAN:
Aux parameters: Max,
Min, P-P, Adev, Std
VALUE Stat parameters dis-
appear
Table 2-3 Keyboard test.

Short Form Specification
Test
Sensitivity and Frequency Range
–Recall the DEFAULT settings.
–Press INPUT A.
–Select 50 Winput impedance, 1x attenuation, MANual
trigger and Trigger level 0V.
–Connect a signal from a HF generator to a BNC power
splitter.
–Connect the power splitter to Input A of your counter
and an oscilloscope.
–Set the input impedance to 50 Won the oscilloscope.
–Adjust the amplitude according to the following table.
Read the level on the oscilloscope. The timer/counter
should display the correct frequency.
–Connect the signal to Input B.
–Press INPUT B.
–Select 50 Winput impedance, 1x attenuation, MANual
trigger and Trigger level 0V.
– Press MEAS FUNC ®Freq ®Freq A ®B
– Repeat the measurements above for Input B.
Voltage
–Recall the DEFAULT settings.
–Press MEAS FUNC ®Volt ®Vpp ®A
–Press INPUT A and select DC coupling. Do not apply an
input signal to Input A yet.
–Press EXIT/OK.
–The display should now indicate
(disregard the main parameter VPP):
VMIN = 0 ± 0.015 V and
VMAX = 0 ± 0.015 V
–Adjust the current limit of the voltage source to
<200 mA.
–Connect +2.500 VDC to Channel A, using the external
low-pass filter on the input.
–The display should now indicate:
VMIN = 2.500 ± 0.040 V and
VMAX = 2.500 ± 0.040 V
–Repeat the measurement with inverted polarity.
–Press INPUT A and select 10x.
–Press EXIT/OK.
CAUTION: Before the next step, make sure
the input impedance is still 1 MW. Apply-
ing more than 12 V without proper current
limiting may cause extensive damage to
the main PCB, if the impedance is set to
50 W.
–Change the DC level to +50.00 V.
–The display should now indicate:
VMIN = 50.00 ± 0.65 V and
VMAX = 50.00 ± 0.65 V
–Repeat the measurement with inverted polarity.
–Disconnect the DC voltage from Channel A.
–Remove the external low-pass filter.
–Press INPUT A and select 1x.
–Press EXIT/OK.
–Connect a sinusoidal signal to Input A with an amplitude
of 4.000 Vpp and a frequency of 100 kHz.
– The display should now indicate: 4.000 ± 0.150 VPP.
– Press INPUT A and select 10x.
– Press EXIT/OK.
– Change the amplitude to 18.00 VPP.
– The display should now indicate:
18.00 ± 0.84 VPP.
– Disconnect the signal from Channel A.
– Press MEAS FUNC ®Volt ®Vpp ®B
– Press INPUT B and select DC coupling. Do not apply an
input signal to Input B yet.
–Press EXIT/OK.
–The display should now indicate
(disregard the main parameter VPP):
VMIN = 0 ± 0.015 V and
VMAX = 0 ± 0.015 V
–Proceed by repeating the measurements for Input B as
described above for Input A.
Trigger Indicators vs. Trigger Levels
NOTE: This test must be performed in the sequence given.
–Recall the DEFAULT settings.
2-4 Performance Check, Short Form Specification Test
Trigger Level
(manually set)
Trigger Indicator Pass
Input A Input B
+1 V off
-1 V on
0.0 V blinking
Table 2-4 Trigger indicator check.
Frequency
(MHz)
Level Pass/Fail
mVrms dBm Input A Input B
10 15 –23
50 15 –23
100 15 –23
200 15 –23
300 25 –19
Table 2-5 Sensitivity for inputs A & B at various frequencies

–Press INPUT A and select MANual trigger level and 50 W
input impedance.
–Connect the LF synthesizer to Input A. Use the follow-
ing settings (into 50 W):
Sine, 10 kHz, 0.9 VPP, and +0.50 VDC.
–Verify that the three modes for the trigger indicator are
working properly by changing the trigger level:
–Press the Trig key and enter +1 V via the keyboard,
then verify by pressing EXIT/OK. Check the trigger
indicator according to Table 2-4.
–Press the Trig key and enter –1 V via the keyboard
by pressing the ±key, then verify by pressing
EXIT/OK. Check the trigger indicator according to
Table 2-4.
–Press the Trig key and enter 0 via the keyboard, then
verify by pressing EXIT/OK. Check the trigger indica-
tor according to Table 2-4.
–Apply the signal to Input B instead.
–Press MEAS FUNC ®Freq ®Freq (A) ®B
–Press INPUT B and select MANual trigger level and
50 Winput impedance..
–Repeat the trigger level settings above to verify the three
trigger indicator modes for Input B.
Input Controls
– Recall the DEFAULT settings.
– Connect the LF synthesizer to Input A. Use the same
settings as in the previous test.
– Press INPUT A and select DC and 50 W.
– Press EXIT/OK.
– Check the Vmax and Vmin voltage levels on the display
according to the first row in Table 2-6.
– Perform the rest of the settings in sequence, and read the
corresponding Vmax and Vmin values. Remember that all
these values are approximate and serve only as indica-
tors of state changes.
–Connect the generator to Input B.
–Press MEAS FUNC ®Freq ®Freq (A) ®B
–Press INPUT B and select DC and 50 W.
–Press EXIT/OK.
–Check the Vmax and Vmin voltage levels on the display
according to the first row in Table 2-6.
–Perform the rest of the settings in sequence, and read the
corresponding Vmax and Vmin values.
Reference Oscillators
X-tal oscillators are affected by a number of external condi-
tions like ambient temperature and supply voltage. Aging is
also an important factor. Therefore it is hard to give limits for
the allowed frequency deviation. The user himself must de-
cide the limits depending on his application, and recalibrate
the oscillator accordingly.
To check the accuracy of the oscillator you must have a cali-
brated reference signal that is at least five times more stable
than the oscillator that you are testing. See Table 2-7 and the
list of test equipment on page 2-2. If you use a non-10 MHz
reference, you can use the mathematics in the timer/counter to
multiply the reading.
–Recall the DEFAULT settings. See page 2-2
–Connect the reference to input A
–Check the readout against the accuracy requirements of
your application.
nAcceptance Test
Table 2-7 can serve as an acceptance test and gives a worst
case figure after 30 minutes warm-up time. All deviations that
can occur in a year are added together.
Resolution Test
–Connect the pulse generator to a power splitter.
–Connect one side of the power splitter to Input A on the
counter using a coaxial cable.
–Connect the other side of the power splitter to Input B
on the counter.
Settings for the pulse generator:
–Amplitude = 2 VPP, (high level +2V and low level 0 V)
–Period = approx. 1 ms
–Duration = approx. 50 ns
–Rise time = 2 ns
Restore the timer/counter's default settings and make the fol-
lowing changes:
–Function = Time A-B
–Press STAT/PLOT key to the right of the display.
–Settings for INPUT A and INPUT B:
50 Winput impedance
MANual trigger level
Performance Check, Short Form Specification Test 2-5
Settings Vmax Vmin Pass/Fail
Input A Input B
INPUT A, DC, 50 W+950 mV +50 mV
AC +450 mV -450 mV
10X +0.45 V -0.45 V
1MW>+0.45 V <-0.45 V
Table 2-6 Input controls check.
Oscillator Frequency Readout Suitable
Reference
P/F
Standard
(PM6690/_1_) 10.00000000 MHz ±150 Hz 908
OCXO
(PM6690/_5_) 10.00000000 MHz ±1Hz 909
OCXO
(PM6690/_6_) 10.00000000 MHz ±0.25 Hz 909
Table 2-7 Acceptance test for oscillators.

Trig level = 0.5V
DC coupling
The standard deviation (Std) should be <100 ps.
Rear Inputs/Outputs
10 MHz OUT
–Connect an oscilloscope to the 10 MHz output on the
rear of the counter. Use a coaxial cable and 50 Wtermi-
nation.
–The output voltage should be sinusoidal and above 1
VRMS (2.8 Vp-p).
EXT REF FREQ INPUT
–Recall the DEFAULT settings.
–Connect a stable 10 MHz signal (e.g REF OUT from an-
other counter) to input A.
–Connect a 10 MHz, 100 mVRMS, (0.28 VP-P) signal from
the LF synthesizer to EXT REF IN.
–Select Ext Ref. by keying in the following sequence:
SETTINGS ®Timebase Ref ®Ext
–The display should show 10 MHz.
–Change the external reference frequency to 5 and
1 MHz.
–The counting should continue, and the display should
still show 10 MHz.
EXT ARM INPUT
– Proceed from the test above.
– Select MANual trigger.
– Settings for the pulse generator:
single shot pulse, manual trigger,
amplitude TTL = 0 - 2 VPP, and
duration = 10 ns.
–Connect the pulse generator to Ext Arm Input.
–Activate start arming by keying in the following se-
quence:
SETTINGS ®Start Chan ®E
–The counter does not measure.
–Apply one single pulse to Ext Arm Input.
–The counter measures once and shows 10 MHz on the
display.
Measuring Functions
–Connect a 10 MHz sine wave signal with approx.
1V
RMS amplitude into 50 Wvia a power splitter to Input
A and Input B, e.g. from 10 MHz Out on the rear panel.
–Recall the DEFAULT settings.
Select the following settings for the timer/counter via INPUT
Aand INPUT B:
–50 Wimpedance for A and B.
–MANual trigger.
2-6 Performance Check, Rear Inputs/Outputs
Selected Function Action Display P/F
FREQ A 10 MHz 2)
FREQ B 10 MHz 2)
FREQ C --------------3)
FREQ RATIO A/B 1.0000000
FREQ RATIO C/B 0.0000000 3)
PER SINGLE A 100 ns 2)
PER SINGLE B 100 ns 2)
PER AVERAGE A 100 ns 2)
PER AVERAGE B 100 ns 2)
PULSE POS A 50.000 ns 1)
PULSE NEG A 50.000 ns 1)
TIME INT A to B 0±1ns
Select NEG
SLOPE B 50.000 ns 1)
RISE TIME A Select AUTO
trigger 30.000 ns 2)
FALL TIME A 30.000 ns 2)
PHASE A rel B 180° or -180° 1)
PHASE B rel A 180° or -180° 1)
PHASE A rel A 0°
DUTY POS A 0.500000 1)
DUTY NEG A 0.500000 1)
VOLT MAX A +0.75 V 2)
VOLT MIN A -0.75 V 2)
Table 2-8 Measuring functions check
1) Value depends on the symmetry of the signal.
2) Exact value depends on input signal.
3) If an RF option is installed.

–Check that the timer/counter performs the correct mea-
surement by displaying the result as shown under the
“Display” column in Table 2-8.
–Select function via MEAS FUNC
Check of HOLD OFF
Function
–Recall the DEFAULT settings.
–Select Period Single A.
Select the following common timer/counter settings for both
Input A and Input B via the hard menu keys INPUT A and IN-
PUT B:
–50 Wimpedance.
–DC coupling.
–MANual trigger, x1 attenuation.
–Press SETTINGS and activate Hold Off. Select Hold Off
On and set the Trigger Hold Off time to the minimum
value 20 ns.
–Connect the rear panel output marked 10 MHz OUT to
Input A.
– Increase the Trigger Hold Off time in steps by means of
the UP cursor key and note the results:
If Trigger Hold Off time <100 ns the result is about 100 ns,
i.e. the same value as without Hold Off.
If Trigger Hold Off time >100 ns the result is about 100 ns +
Trig Hold Off time.
– Connect the signal to Input B, select
Period Single B and repeat the tests above.
RF Options
Input C Check
To verify the specification of the different RF prescalers
(Input C), use the following basic test setup:
–Connect the output of a signal generator covering the
specified frequency range to the RF input of the counter.
–Connect the 10 MHz REF OUT from the generator to
the EXT REF IN on the rear panel of the counter.
–Choose Meas Ref from the SETTINGS menu and select
External.
–Choose Freq C from the MEAS FUNC menu.
–Generate a sine wave in accordance with the tables.
–Verify that the counter is counting correctly. (The last
digits will be unstable)
Performance Check, Check of HOLD OFF Function 2-7
Frequency Amplitude P/F
MHz mVRMS dBm
100-300 20 -21
300-2500 10 -27
2500-2700 20 -21
2700-3000 40 -15
Table 2-9 RF input sensitivity,
3 GHz Option.
Frequency Amplitude P/F
MHz mVRMS dBm
300-500 20 -21
500-3000 10 -27
3000-4500 20 -21
4500-6000 40 -15
6000-8000 80 -9
Table 2-10 RF input sensitivity,
8 GHz Option.

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2-8 Performance Check, RF Options

Chapter 3
Disassembly

The terms in the following figure are used in all descriptions
in this manual.
The PM6690 can be equipped with a number of options and
accessories. Built-in timebase and prescaler options can be
identified by pressing USER OPT ®About on the front
panel.
The following built-in options exist or are planned:
–Option PM6690/6__ 3 GHz RF Prescaler Input
–Option PM6690/7__ 8 GHz RF Prescaler Input
–Option PM6690/_5_ Very High Stability OCXO
– Option PM6690/_6_ Ultra-High Stability OCXO
The location of these optional parts is illustrated in Fig. 3-2
and Fig 3-3. Removing the Cover
WARNING: Do not perform any internal ser-
vice or adjustment of this instrument
unless you are qualifyed to do so.
WARNING: When you remove the cover you
will expose live parts and accessible ter-
minals which can cause death.
WARNING: Although the power switch is in
the OFF position, line voltage is present
inside the instrument. Use extreme cau-
tion.
WARNING: Capacitors inside the instrument
can hold their charge even if the instru-
ment has been separated from all voltage
sources.
–Make sure the power cord is disconnected from the
counter.
–Turn the counter upside down.
–Remove the two screws at the bottom and the two
screws in the rear feet.
–Remove the four decorative plugs (C) that cover the
four screw holes on the right and left side of the front
panel.
–Grip the front panel and gently push at the rear.
3-2 Disassembly, Removing the Cover
Front Bottom
Right
Rear
Top
Left
Figure 3-1 Terms used in this manual.
Rear Panel Inputs
Basic Board
Power Supply
RF Inputs
3GHz&8GHz
Input Amplifier
Optional
Oscillator
Fan
Figure 3-2 Interior layout including 3 GHz or 8 GHz
prescaler option.
RF Input 20 GHz
Figure 3-3 Interior layout with 20 GHz prescaler option.