Fluke PM6685R, PM6685 Service Manual

Programmable
Frequency Counter

PM6685 & PM6685R

Service Manual

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.

4822 872 20106

First Edition (May 2003)

No part of this manual may be copied without the express permission of the copyright owner.

All product names are trademarks of their respective companies.

Ó 2003 Pendulum Instruments AB

All rights reserved. Printed in Sweden.

Contents

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

This page is intentionally left blank.

Chapter 1

Safety Instructions

WARNING: These servicing instructions are for use

by qualified personnel only. To reduce the risk of
electric shock, do not perform any servicing other
than that specified in the Operating Manual unless
you are fully qualified to do so.

Authorized service and calibration of this instrument is available
through your Fluke representative. See address at the end of this
manual.

Read this chapter carefully before you check, adjust, or repair an in
strument.

The ground symbol on the rear panel indicates where the
protective ground lead is connected inside the instrument.
Never remove or loosen this screw.

When the instrument is brought from a cold to a warm environment,
condensation may cause hazardous conditions. Therefore, ensure
that the grounding requirements are strictly met.

Power extension cables must always have a protective ground con
ductor.

-

Indicates that the operator should consult the manual.

-

Caution and Warning Statements

You will find specific warning and caution statements where neces
sary throughout the manual.

CAUTION: Indicates where incorrect operating proce

dures can cause damage to, or destruction of,
equipment or other property.

WARNING: Indicates a potential danger that requires

correct procedures or practices in order to prevent
personal injury.

This Timer/Counter has been designed and tested in accordance with
safety class 1 requirements for Electronic Measuring Apparatus of
IEC (CENELEC) publication EN61010-1, and CSA 22.2
No. 1010-1, and has been supplied in a safe condition.

This manual contains information and warnings that should be fol
lowed by the user and the service technician to ensure safe operation
and repair in order to keep the instrument in a safe condition.

WARNING: Opening instrument covers or removing

parts, except those to which access can be gained
by hand, is likely to expose high voltages which
can cause death.

The instrument must be disconnected from all voltage sources before
it is opened. Remember that the capacitors inside the instrument re
tain their charge even if the instrument has been disconnected from
all voltage sources.

-

Grounding

This instrument is connected to ground via a sealed three-core power
cable, which must be plugged into socket outlets with protective
ground contacts. No other method of grounding is permitted for this
instrument.

WARNING: Any interruption of the protective ground

-

conductor inside or outside the instrument, or dis
connection of the protec- tive ground terminal, is
likely to make the instrument dangerous. Do not in
tentionally disrupt the protective grounding.

-

-

Disposal of Hazardous Materials

WARNING: Disposal of lithium batteries requires spe

cial attention. Do not expose the batteries to heat
or put them under extensive pressure. These mea
sures may cause the batteries to explode.

A lithium battery is used to power the nonvolatile RAM in this in
strument. Our world suffers from pollution, so don’t throw batteries
into your wastebasket. Return used batteries to your supplier or to the
Fluke representative in your country.

-

-

-

-

Line Voltage

The instrument can be powered by any voltage between 90 and
265 V
inal line voltages between 100 and 240 V.

n

Components that are important for the safety of this instrument may

-

only be replaced by components obtained from your local Fluke
representative. After exchange of the primary circuits, perform the
safety inspection and tests, as described in Chapter 5, “Repair”.

n

This instrument is protected by an ordinary 1.6 A slow blow fuse
mounted inside the instrument. NEVER replace this fuse without
first examining the Power Supply Unit.

without range switching. This makes it suitable for all nom

AC

Replacing Components in Primary Circuits

Fuses

-

1-2 Safety Instructions,

Chapter 2

Performance Check

General Information

Ω

WARNING: Before turning on the instrument, ensure

that it has been installed in accordance with the In
stallation Instructions outlined in Chapter 3 of the
Operators Manual.

This performance procedure is intended to:

Check the instrument’s specification.

–

Be used for incoming inspection to determine the acceptability

–

of newly purchased instruments and recently recalibrated in
struments.

Check 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 cover of the instrument to perform
this procedure.

If the test is started less than 20 minutes after turning on the instru
ment, results may be out of specification, due to insufficient
warm-up time.

-

-

Preparations

Power up your instruments at least 20 minutes be
fore beginning the tests to let them reach normal
operating temperature. Failure to do so may result
in certain test steps not meeting equipment specifi
cations.

-

-

Front Panel Controls

Power-On Test

At power-on the counter performs an automatic self-test of the fol

-

-

lowing:

Microprocessor

–

–

RAM

ROM

–

Measuring circuits

–

Display

–

If a GPIB interface is installed, the GPIB address is displayed.

If there are any test failures, an error message is shown.

Turn on the counter and check that all segments light up on the

–

display and that no error message appears.

-

Recommended Test
Equipment

Type of instru

ment

LF Synthesizer Square;

Power Splitter 50 W PM9584/02
T-piece
Termination 50 W PM9585

Reference oscilla
tor

HF signal genera
tor

Pulse Generator 125 MHz
Oscilloscope with

probes
BNC cables 5 to 7 cables *

Table 2-1 Recommended Test Equipment.

*) Two of the cables must have 10 ns difference in delay, for ex

ample: 5 ns and 15 ns.

-

-

-

Required

Specifications

Sine up to 10 MHz

10 MHz ±0.1 Hz for
standard oscillator

10 MHz ±0.01 Hz for
PM9691 & PM9692

10 MHz ±0.0001 Hz
for PM6685R

0.5 GHz (no presc.)

3.3 GHz (option 10)

350 MHz

Suggested

Equipment

Fluke counter with
calibrated option

PM9691
Fluke PM6685R or

PM6681R
Fluke 910R or Ce

sium Standard

-

Fig. 2-1 Text on the display.

Internal Self-Tests

The different built-in test routines invoked by the power-on test can
also be activated from the front panel as follows:

Enter the Auxiliary Menu by pressing AUX MENU.

–

Select the test submenu by pressing DATA ENTRY up or

–

down.

Enter the test menu by pressing the ENTER key.

–

Selections 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)

Use DATA ENTRY up/down to select TEST ALL, then press

–

ENTER.

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 measuring

-

–

mode.

-

2-2 Performance Check, General Information

Keyboard Test

The keyboard test verifies that the counter responds when you press
any key. To check the function behind the keys, see the tests further
on in this chapter.

Press the keys as described in the left column and look on the display
for the text, as described in the second column. Some keys change
more text on the display than described here. The display text men
tioned here is the text mainly associated with the selected key.

Key(s) Display Note Pass

STAND-BY Display Off Red LED

ON Backlight on

PRESET

ENTER

EXT REF EXT REF

Input A

FILTER FILTER

50 W

(2 times)

SENS 
(2 times)

SENS 
(2 times)

AUTO AUTO TRIG

PRESET

ENTER

MEAS TIME 200
DATA ENTRY  500
DATA ENTRY  200

ENTER NO SIGNAL

DISPLAY HOLD HOLD

DISPLAY HOLD

SINGLE SINGLE

FUNCTION  DUTY F A
FUNCTION  TOT A MAN

FUNCTION  DUTY F A
FUNCTION  FREQ A

AUX MENU RECALL

MEAS RESTART NO SIGNAL

PRESET

ENTER

CHECK 10.00000000

NULL NULL
NULL 10.00000000

BLANK DIGITS

(3 times)

MENU Displays all avail

DEFAULT?

NO SIGNAL

50 W

Bar graph:

zzzzzzzz

Bar graph:

zzzzzzzzzz

Other

DEFAULT?

NO SIGNAL

DEFAULT?

NO SIGNAL

10.00000___

able functions, pro

cesses and input

controls. Selected

items are blinking.

–3

s

–3

s

–3

s

6

Hz* Start

6

Hz*

6

Hz*

counting

-

-

Table 2-2 Keyboard Test.

beside

the key

On

Default

setting

Default

setting

Default

setting

/Fail

NOTE: For the instrument to respond correctly, this test must

be carried out in sequence and you must start with the
preset (power-on) setting.

* The LSD may vary.
** MENU is not disabled by setting DEFAULT; press menu again.

-

Short Form Specification
Test

Sensitivity and Frequency Range

Press the PRESET key to set the counter in the default setting.

–

Then confirm by pressing ENTER.

Turn off AUTO.

–

Select IMP A = 50 W and 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 W on the oscilloscope.

–

Adjust the amplitude according to the following table. Read

–

the level on the oscilloscope. The counter should display the
correct frequency.

Frequency Level Pass/Fail

MHz mV

1 30 10 –27

25 30 10 –27

50 30 10 –27
150 60 20 –21
200 90 30 –17
250 150 50 -13

300 150 50 -13

PP

mV

RMS

Table 2-3 Sensitivity of input A at various frequencies.

Reference Oscillators

X-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. Therefore, it is hard to give limits for the allowed
frequency deviation. You must decide the limits depending on your
application, and recalibrate the oscillator accordingly. See the Pre
ventive Maintenance in the Repair chapter, Chapter 5.

Oscillator Max. tempera

Standard ±100 Hz ±5 Hz ±50 Hz

PM9691 ±0.05 Hz ±0.1 Hz ±0.75 Hz

PM9692 ±0.025 Hz ±0.03 Hz ±0.2

Rubidium ±0.003 Hz ±0.0005 Hz ±0.002 Hz

ture dependence

Table 2-4 Deviation (for PM9691 and PM9692 after a

warm-up period of 48 hours).

To check the accuracy of the oscillator you must have a calibrated
reference signal that is at least five times as stable as the oscillator
that you are testing, see the following table.

Press the PRESET key, then press the ENTER key to set your

–

counter in the Default setting.

-

dBm Input A

Max. aging

per month

-

-

Max. aging

per year

Performance Check, Short Form Specification Test 2-3

Connect the reference to input A.

–

Check the readout against the accuracy requirements of your

–

application.

Acceptance Test

n

As an acceptance test, the following table gives a worst case figure
after a 30 minute warm up time. All deviations that can occur in a
year are added together.

Oscillator Frequency readout Suitable refer

Standard 10.00000000 MHz

±120 Hz

PM9691 10.00000000 MHz

±1 Hz PM6685R

PM9692 10.00000000 MHz

±0.25 Hz

ence

PM9691

PM6681R

Pass

­/Fail

Table 2-5 Acceptance test for oscillators.

Acceptance Test, PM6685R

n

To fully test the accuracy of the PM6685R, a reference signal of ex
tremely high stability is needed. Examples of such references are
Cesium Atomic references, or transmitted signals from a nationally
or internationally traceable source, like the GPS satellites.

EXT ARM INPUT

Press the PRESET key, then press the ENTER key to set your

–

counter in the Default setting.

Select 50 W input impedance.

–

Apply 10 MHz 500 mV

–

–

The counter measures and displays 10 MHz.

Press the AUX MENU key.

–

Press the DATA ENTRY UP/DOWN keys until the display

–

shows ‘Ar. Start’, confirm by pressing the ENTER key.

Press DATA ENTRY UP/DOWN keys until the display shows

–

‘POS’, confirm by pressing the ENTER key.

Press the ENTER key once more.

–

The counter does not measure.

–

Connect a pulse generator to Ext Arm input.

–

Settings for pulse generator: single shot pulse, amplitude TTL

–

=0-2V

Apply one single pulse to Ext Arm input.

–

-

The counter measures once and shows 10 MHz on the display.

–

, and duration = 10 ns.

PP

, (1.4 VPP) sine to input A

RMS

Recommended Test Equipment

Type Stability Model

10 MHz refer

ence

-

£ 1x10

-10

910R with satellite contact dur

ing the last 72 hours.

Test Procedure

Connect the counter to the line power.

–

Check that the UNLOCK indicator turns on, and then turns off

–

again within 6 minutes after connecting line power.

Connect the 10 MHz reference signal to input A of the counter.

–

Select FREQUENCY A measurement.

–

Select 2 s measuring time.

–

Check that the displayed frequency is 10.00000000 MHz

–

±0.05 Hz £ 10 minutes after connection to line power.

Rear Input/Output

INT REF Output

Connect an oscilloscope to the 10 MHz output on the rear of

–

the counter. Use coaxial cable and 50 W termination.

The output voltage is sinusoidal and should be above 2.8 VPP.

–

EXT REF Input

Press the PRESET key, then press the ENTER key to set your

–

counter in the Default setting.

Apply 10 MHz sine to input A equipped with a T-piece and to

–

Ext Ref input at the rear, terminated with 50 W. Amplitude on
10 MHz signal; 200 mV

–

Press the Ext Ref key.

The display should show 10.000000006Hz ± 5 LSD.

–

, (560 mVPP)

RMS

Measuring Functions

-

Preparation for Check of Measuring Function is as follows:

Connect a 10 MHz sine wave signal with 2.0 VPPamplitude

–

via a T-piece to Input A.

Connect a cable from the T-piece to Input E (Ext Arm) at the

–

rear.

Select the measuring function as in the ‘Selected Function’ col

–

umn and check that the counter performs the correct measure
ment by displaying the result as shown under the “Display”
column in the following table.

Selected Function Display Pass/ Fail

PRESET

ENTER

IMPA50W 10 MHz

Non AUTO 10 MHz

PER A 100 ns

RATIO A/E 1.0000000
PWIDTH A 50 ns

TOT A MAN

DISPLAY HOLD Start counting
DISPLAY HOLD Stop counting

DUTY FACT 0.500000

AUTO 0.500000

DEFAULT?

10 MHz

2)

1)

2)

2)

2)

1)

1)

Table 2-6 Measuring functions check.

1) Value depends on the symmetry of the signal.

2) Exact value depends on the input signal.

-

-

2-4 Performance Check, Rear Input/Output

Options

Prescaler

This extra HF input (PM9624) is easily recognized by its front panel
connector (Input C, type N).

EX T
REF

Fig 2-2 Connect the output of the signal generator to the HF

Required Test Equipment Suggested Specification

HF signal generator 3.3 GHz

Table 2-8 Test equipment for 3.0 GHz HF input.

Connect the output of the signal generator to the HF input of

–

the counter.

Connect the 10 MHz REFERENCE OUT of the generator to

–

the REFERENCE IN at the rear panel of the counter.

Setting for the counter after Preset.

Function = FREQ C.

–

EXT REF.

–

Generate a sine wave in accordance with the following table.

Verify that the counter counts correctly. (The last digit will be

–

unstable).

Table 2-7 Sensitivity of the PM9624 HF input.

input of the counter.

Frequency Amplitude Pass/Fail

MHz mV

100-300 20 –21

-2500 10 –27

-2700 20 –21

-3000 100 –7

RMS

dBm

Performance Check, Options 2-5

This page is intentionally left blank.

2-6 Performance Check, Options

Chapter 3

Disassembly

The terms in the following figure are used in all descriptions in this
manual.

To p

Left

Front Bottom

Fig. 3-1 Designations used in this manual.

The PM6685 is available with a number of options and accessories.
The labels on the rear panel of the counter identify the options and
accessories included. If there are no labels, the counter contains an
uncompensated crystal oscillator and no options. The following la
bels exist:

PM9624 3.0 GHz HF input

–

PM9691 High-Stability Oven Oscillator

–

PM9692 Ultra-High-Stability Oven Oscillator

–

PM9626B GPIB Interface

–

The location of these optional parts is illustrated in Fig.3-2.

GPIB interface

Power
Module

G1

Optional
oscillator

Rear

Right

Removing the Cover

WARNING: Do not perform any internal service or ad

justment of this instrument unless you are qualified
to do so.

WARNING: When you remove the cover you will ex

pose high voltage parts and accessible terminals
which can cause death.

WARNING: Although the power switch is in the off

position, line voltage is present on the printed cir
cuit board. Use extreme caution.

WARNING: Capacitors inside the instrument can hold

their charge even if the instrument has been sepa
rated from all voltage sources.

–

Make sure the power cord is disconnected from the counter.

Turn the counter upside down.

-

–

Loosen the two screws (A) at the bottom and the two screws

–

(B) in the rear feet.

Grip the front panel and gently push at the rear.

–

Pull the counter out of the cover.

–

A

Fig. 3-3 Remove the screws and push the counter out of

the cover.

A

B

B

-

-

-

-

HF input

Main board

Front panel

Fig. 3-2 Location of the boards in the counter.

Reinstalling the Cover

Gently push the counter back into the cover.

–

Turn it upside down.

–

Install the two screws (A) at the bottom.

–

Install the two rear feet with the screws (B) to the rear panel.

–

PM9624 (HF Input)

Disconnect the power cable.

–

Remove the cover from the counter.

–

Disconnect the cable from the mini-coax connector (A) on the

–

HF input.

Press the clips (B) apart and lift the HF input pca straight up

–

and out.

3-2 Disassembly, Removing the Cover

When installing the HF input, make sure that the connector

–

pins fit exactly in the holes in the connector housing (C).

A

B

C

B

PM9691 or PM9692 (Oven
Oscillator)

Disconnect the power cable.

–

Remove the cover of the counter.

–

Remove the two screws (A) holding the oscillator to the main

–

pca from underneath.

Press the clip (B) gently to the front of the counter and lift the

–

oscillator straight up.

Make sure that jumpers J14 and J15 are set in the correct posi

–

tion.

When fitting the oscillator, make sure that the connector pins

–

fit exactly in the holes in the connector housing.

A

-

Fig. 3-6 Removing the HF Input.

PM9626 (GPIB Interface)

Disconnect the power cable.

–

–

Remove the cover from the counter.

Loosen the two screws (A) holding the GPIB interface to the

–

rear panel.

Disconnect the interface cable from P103.

–

Move the GPIB interface pca toward the front of the counter

–

and lift the pca supports out from the “keyholes” (B) on the
main PCA.

A

B

B

Fig. 3-5 One of the two screws holding the oven oscillator

in place.

A

Fig. 3-4 Loosen the two screws in the rear panel and dis

engage the board from the keyholes.

-

Disassembly, PM9626 (GPIB Interface) 3-3

This page is intentionally left blank.

3-4 Disassembly, PM9691 or PM9692 (Oven Oscillator)

Chapter 4

Circuit Descriptions

Block Diagram Description

General

The PM6685 Frequency Counter consists of three main units:

Front unit

–

Main board unit

–

Rear panel unit

–

The following options can be added:

GPIB interface including analog output (PM9626B)

–

–

Prescalers 1.3 GHz (PM9621), 3.0 GHz (PM9624)

Oven-controlled crystal oscillators (PM9691 or PM9692)

–

Rack mount adapter (PM9622/02)

–

Battery option (PM9623)

–

The chassis of the counter consists of a front piece molded in alumi
num, an aluminum rear panel, and two profiled aluminum rods that
hold the front and rear panels together. This unit can be slid into the
aluminum cover of the instrument.

The front unit contains all functions needed for the user communica
tion. It is connected to the main board unit with a flat cable, and the

molded front unit is fixed to the two profiled aluminum rods with
screws.

The main board unit consists of a PCB mounted on two profiled alu
minum rods. Most functions, such as the following, are placed on the
main board:

Input amplifiers with trigger level circuits

–

Power supply

–

–

Measurement logic

Microcomputer circuitry

–

Some outputs, such as the trigger levels and probe compensation
view outputs are directly mounted on the main board.

The rear panel unit is of aluminum with a number of mounted con

-

-

nectors. Most of the connectors are soldered directly to the main
board. The rear panel is fixed to the two profiled aluminum rods with
screws.

-

-

4-2 Block Diagram Description

Optional oscillator

A

X2
EXTC

INTREF

10 MHz out

G

B2

E

External arming

÷2

EXTREF
A

A2

C

HF input

GET

D

A

External reference

Input Amplifier

U29

Counter

ASIC

Micro-

computer

Trigger DAC´s

Local preset

Reset circuit

HSI.0

RESET

U11

2

IC

PWM

Gate LED

Display

Analog output

Option 80

Power supply

C

90-265 V

+5V
+12V

GPIB option

+7V

-5.2V

Keyboard

Fig. 4-1 PM6685 block diagram.

Block Diagram Description 4-3

Hardware Functional Description

Front Unit

LCD Drivers

U201
Driver 1

SCL

SDA

PC F8 576

Sync.

U2 02
Driver 2
PC F8576

Fig. 4-2 Front panel LCD drivers.

An LCD and two LEDs are used as indicators. The LCD is used to
show both the measurement result and the state indicators of the in
strument setting. The LEDs show standby and gating.

The LCD has 158 segments that are multiplexed with a ratio of 2:1.
Two parallel and synchronized LCD drivers (U201 and U202) are
used. They are connected with a serial I
on the main board. The clock frequency of the drivers is approxi
mately 140 kHz, set by R201. The VLCD pin is connected to GND
on the main board.

The LCD is provided with a backlight, an LED array integrated into
one component. Its current consumption is set by the resistors
R204-R207. The backlight dissipates approximately 1.5 W .

Backpl. 0

Backpl. 1

LC D

1 58 segment s

2:1 Multiplex

2

C bus to the microcomputer

Keyboard

Main Board

U11

AD0-AD7 H0-H3

CPU

HS1.0

P1.1

P1.0

-

Fig. 3 Keyboard scanning.

-

The front panel pushbuttons are connected in a matrix. The scanning
signals H0 to H3 come from the main board. If a push button is
pressed and H0 to H3 is high, one of the output signals V0 to V7 will
be high. The STAND-BY/ON and LOCAL-PRESET buttons are not
part of the scanning but are connected directly to the main board.

The front unit is fixed to the main board unit with three screws. The
electrical connection is made with a 40-lead flat cable to the main
board.

U13A

Latch

U14A

Latch

AD0-AD7

Keyboard & Display

Board

V0-V7

LOCAL/PRESET

SCL
SDA

4-4 Hardware Functional Description

Main Board

Introduction

Components not necessary for explaining the function are omitted
from the figures in this chapter. For the complete set of components,
see the circuit diagrams in Chapter 8, Drawings and Diagrams.

Input Amplifier

The input amplifier has 300 MHz bandwidth and is of the split-band
type. It contains four main stages: the signal adaptation stage, the im
pedance converter stage, the comparator stage, and the buffer stage.

Signal Adaptation

n

This part of the amplifier contains:

50 W/1 MW impedance selector

–

x1/x11 attenuator

–

Voltage limiter

–

50 W /1MW Impedance Selector

K2

C2

R6

J1

R1

K1

R7-R17

C1

R2 R3-R5

R22-R23

R18

K3

R19­R20

R24­R26

C3

To Voltage
li mi te r

R27­R28

selected if the relay is open. Depending on selected attenuation, the
1MW input impedance is determined by different combinations of
resistors.

In x1 attenuation mode (K2 is closed and K3 is open) the impedance
is determined by resistor network R22 to R28.

In x11 attenuation mode (K2 is open and K3 is closed) the same net

­work as in the x1 case is involved plus the resistors R3 to R5 and R18
to R20.

The input capacitance in parallel with 1 MW is 24 pF at x1 attenua

-

tion and 12 pF at x11 attenuation.

-

The series resistor R1 immediately after the selector serves both as
current limiter together with the voltage limiter (see below) and as
impedance matching resistor. The resistor also improves the Volt

­age-Standing-Wave-Ratio (VSWR) of the amplifier input.

x1/x11 Attenuator

The x1 attenuator consists of a resistive low-frequency divider,
which reduces the input signal by a factor of 2, and a capacitive
high-frequency divider. The attenuator is formed by the resistors
R22-R23 andR24-R26 in parallel with R27-R28. The capacitive part
is formed by the variable capacitor C2 in parallel with R22-R23, and
the parasitic capacitance across R24-R26.

The capacitive attenuator is adjusted via variable capacitor C2 to the
same attenuation value as the resistive attenuator.

The x11 attenuator also consists of a resistive low-frequency divider
and a capacitive high-frequency divider. The resistive part is formed
by R1-R5, and R18-R20 in parallel with 1 MW (the x1 attenuator im
pedance). The capacitive divider is formed by the variable capacitor
C1 and the parasitic capacitance at the node where R5, R18 and R22
meet.

-

Fig. 4-4 Impedance selector and 1X/11X attenuator.

The 50 Wor1MW impedance modes are selected by relay K1. 50 W
is selected via the resistors R7 to R17, if the relay is closed. 1 MW is

Input A

Imp. Att. Limiter

Imp.

Conv.

Trigger
level Comp I

Trigger
level Comp II

Resistors R2 and R6 improve the frequency response.

LP

filter

Comp-

arator

Flip­Flop

Comp-

arator

÷2

Buffer

Buffer

A

A2

Fig. 4-5 Input amplifier block diagram.

Hardware Functional Description 4-5

Voltage limiter

p

+5

and D3 to clamp positive voltage and resistor R36 plus the diodes D2
and D4 to clamp negative voltage. The clamp voltage is approxi
mately ±2.1 V for low frequency signals. At high frequency the
clamp voltage rises to approximately ±2.3 V.

-

R35

D3D1

From
Attenuator

D2

R36

-

To Impedance
converter stage

D4

Fig. 4-6 Voltage limiter.

A voltage limiter that protects the impedance converter against
overvoltage is placed between the attenuator and the impedance con
verter. The voltage limiter consists of resistor R35 and the diodes D1

Impedance Converter Stage

n

The analog signal from the input stage is fed to an amplifier stage
where split-band technique is used to get good frequency response
over a wide range. This means that the high-frequency contents of
the signal are fed to a high-impedance AC-coupled FET transistor
stage Q1. The low-frequency contents are fed to a DC-coupled oper

­ational amplifier stage with negative feedback from the output of the
converter stage buffer. The low-frequency path handles frequencies
up to approximately 5 kHz.

The high-frequency signal is fed to the gate of Q1. The high imped

­ance at the gate is converted to a low impedance at the source. The
source is connected to the base of HF transistor Q2, the summing
point for the two signal paths.

To make the FET work well in its active region within the whole dy

­namic range, the FET drain is supplied with +7 V via resistor R42.

The low-frequency signal is divided by the two resistors R27 and
R28 before it is coupled to the input pin #2 of the operational ampli
fier U1. The resistors R37 and R38 at the operational amplifier out

-

­put pin #6 center the output swing, and capacitor C6 stabilizes the
operational amplifier stage.

-

The low-frequency path goes from the operational amplifier to the
base of transistor Q3, the collector of which is connected to the base

Fr om Pr o t ec t io n
ci rcu its

R27

R28

R32

C13

R33

R29­R30

R31

C5

+7 +5

R42 R43

Q1

-5.2

R37

R38

-5.2 -5.2 -5.2 -5.2 -5.2

Q3

C6

+5

Q2

R105

R46

R47

Q13

C20

R50

K4

L1

C18-

Q4U1

C19

K4

R106

U8

To

+

-

+

-

Flip-Flo

Trig
Level

Fig. 4-7 Impedance converter.

4-6 Hardware Functional Description

of transistor Q2. This point is common to the high and low frequency
paths.

A buffer amplifier with high driving capacity is used to get a linear
output in the 100 W load resistor R106 over a swing of 2 V. This am
plifier consists of a driver stage Q2, an output stage Q13, and a cur
rent generator Q4.

From the output of this second amplifier stage, the signal is fed back
to theop amppin 3via thedivider chainR29 toR32. Thetrimmer po
tentiometer R31 sets the gain of the low-frequency path equal to the
high-frequency gain of about 0.9. Capacitor C5 is connected to oper
ational amplifier pins #1 and #8 to achieve stable operation. The
trimmer potentiometer R33 between pins #1 and #5 on the opera
tional amplifier is used for adjusting the offset voltage of the opera
tional amplifier.

The channel A filter connected to the output of the second amplifier
stage isa 100kHz low-pass LC filter. It consists of the coil L1 and the
two capacitors C18 and C19 in parallel. The filter is controlled by the
relay K4. The filter output is connected to the input of the comparator
stage.

Comparator Stage

n

The comparator stage converts the analog signal from the impedance
converter stage to a square wave. This circuit consists mainly of the
high-speed integrated comparators U8A and U8B plus a separate
trigger level circuit connected to the comparators at pins 9 and 13 via
resistors R87 and R88.

The trigger level circuits, which are described later, generate a DC
level in the range of approximately æ1.6 V. This covers a dynamic
range of 6.4 V since the input signal is divided by a factor of 2 before

-

-

-

-

-

-

it reaches the comparator.

The counter is provided with adjustable hysteresis, i.e., it is control
lable via the front panel or GPIB. The circuitry for setting the hyster
esis consists of the resistor network R91 to R96, supplied with +5 V
and –5.2 V. It is connected to the latch enable inputs of the compara
tor, pin 5 and 7 for Comparator I and pin 17 and 15 for Comparator II.

The input signal is fed to both comparators, the outputs of which are
used for setting/resetting the Flip-Flop U9.

Buffer Stage

n

Before the signal is fed further into the ASIC U29, it has to be
level-shifted by a buffer stage. The negative ECL logic levels
(~ –0.9 V to ~ –1.7 V) from U9 pins 17 and 18, are converted to a

single-ended signal with CMOS logic levels ( ~ 5 V to~0V).

The buffer is a differential amplifier consisting of the two transistors
Q32 and Q33 whose bases are fed differentially from the two com
parator outputs. Resistor R304 serves as a current generator that is
switched alternately to the two collector resistors R296 and R297.

-

-

-

-

Trigger Level Circuits

The trigger level circuits generate the trigger voltage levels to the in
put comparators. The trigger level range is –3.2 V to + 3.2 V with a
maximum resolution of 0.6 mV. The input amplifier attenuation is

-

TP27 TP26

Trig ger Level I

Input signal

Tri gger Level II

+5

B
A

R92

C

D

R93

E

R91

F

R94

R96

-5.2

R87

B

A

G

U8A

+

-

U8B

+5

R296

U9

D

Flip ­Flop

E

U9

Q32

F

R297

Q33

F

To
Counter
circuits

G

R88

C

+

-

R304

Fig. 4-8 Comparator flip-flop and buffer stages.

-5.2

Hardware Functional Description 4-7

approximately 2 times. The trigger level circuits generate a DC level
that has the same attenuation. This means that the output of this cir
cuit has a range of –1.6 V to +1.6 V with a resolution of maximum

0.3 mV. Adual 8-bit DAC is used. The DACs only generate voltages
between 0 and +1.6 V, but by using a X2 amplifier and an offset shift
of 50%,the voltagerange of –1.6 Vto +1.6V is achieved. The supply
voltages to the trigger level circuits are filtered by R and C to prevent
noise originating in the digital circuitry from influencing the trigger
levels. The ground plane under the trigger level circuits is separated
from the rest of the ground plane, and the planes are connected only
at the front of the counter.

The trigger level circuits consist of the following:

­Resistor network R57 to R68 for generating the reference volt

–

-

ages 0.04 V, 0.22 V, 0.59 V, and 1.6 V.

Three multiplexers (U3) to select one of the levels. With this

–

arrangement there is a total trigger level range of
–1.6 V to +1.6 V.

A double DAC (U4).

–

Two current-to-voltage converters U6. These circuits convert

–

the current at the IOUT pins of the DACs to a voltage. This
signal has a range of 0 V to approximately 1.6 V.

Two amplifiers, U7, with an amplification of X2, to generate a

–

signal with a range of 0 V to 3.2 V. Resistors R69 and R70 set
the reference voltage to the amplifier to get the 50 % offset
shift. To get exact voltages, 0.5 % precision resistors are used:
R73-R75, R78-R79 and R80-R82, R85-R86.

The zero adjust of the trigger levels is done with trimmer po

–

-

tentiometers R69 and R70 connected to the amplifiers in U7.

Two low-pass filters R87-C29 and R88-C30.

–

AD0-AD2

1.6V

0 .59V
0 .22V
0 .04V

U3

AD0- A D8

U4

D0- D7
+DACA

VREFR FB

IOUT

VREFR FB

IOUT

U6

U6

R73-R74

R75

R69

R80-R81

R82

R70

+5

-5.2

+5

-5.2

Trig ger lev el Comp I

R78-R79

U7

R87

C29

Trig ger l evel

Comp II

R85-R86

U7

R88

C30

Compar ator I

Comparator II

Fig. 4-9 Trigger level circuits.

4-8 Hardware Functional Description

Power Supply

General survey

n

The power supply generates four regulated DC supply voltages to the
counter, as well as some other supply voltages for special purposes.
The power supply block also contains the ON/STANDBY logic.

The main building block of the power supply is a primary switch
mode power module (U39). The line power AC voltage (90 V to
265 V) is rectified to a DC voltage before it is fed to the power mod
ule.

After a line power filter in the power inlet, a fuse of 1.6 AT and an
NTC resistor protect the power supply. The fuse F1 should only blow
if a catastrophic error occurs on the primary side of the power supply.
A short-circuit on the secondary side should not affect the primary
side. To minimize the inrush current to the capacitors at the connec
tion of the power cord, an NTC resistor (R148) is used. The resis

tance is 15 Wwhen the resistor is cold but decreases to a few ohms as
it is warmed up by the steady-state current.

The AC voltage is rectified in the bridge rectifier D9 and filtered in
C64. C65 suppresses noise from D9. L6 and C82-C83 serve as a fil
ter at the input of U39.

All inputs and outputs of the power module have HF chokes. The
module is mounted with distance washers on the main board.

-

-

-

From the module there are three DC voltages outputs. One of those is
regulated (+ 5 V) and the others are unregulated. These voltages will
vary with input line voltage, the current at+5V,andattheunregu
lated voltages. The output marked +15 will be approximately +18 V,
and the output marked –7 will be approximately –8 V. The outputs
are filtered; HF is filtered by C70-C73, and LF is filtered by L7-L9
and C74-C76.

-

-

On

Stand by

ains Inlet
M

D9

Filter&Fuse

U42

U

U40B

U39

R156

-7

+5

+15

Power Module

Q14

U43

U

R149-R155

U

U41

J15

K5

R130-R145

K5

U

U21A&Q17

+12 V*

-5.2 V

+5 V

Q5-Q6

+12 V

+7 V

Fan

PM6685R

only

Fig. 4-10 Power Supply.

J31

+-

*) for ON/STBY control & OCXO

Hardware Functional Description 4-9

Function

n

The three DC voltages from the power module are used for
generating the following four supply voltages in the counter:

+5 V

Regulated +5 V from the power module is used directly.

–5.2 V

–7 V is used, with regulator U43.

+12 V

+15 V is used, with regulator U41.

+7 V

Stabilized +12 V is used, with regulator U21A and Q17.

temperature sensor, controls the speed by applying a variable refer
ence voltage to the fan voltage regulator U42.

Counter ASIC

The main part of the counting logic is integrated in a CMOS ASIC
specially designedfor theFluke MultiFunctionCounter series.There
are also analog blocks included in the 100 pin QPF package.

MUX

The MUX block is a switchboard for incoming and internal signals
involved in the measuring process. Some signals are divided by 2 to
make it possible to measure higher frequencies. The trigger slope is
controlled by the MUX block as well. Atrigger edge detector senses
the presence or absence of comparator pulses and controls the trigger
level DAC’s in the TLDAC block. These functional units form an es
sential part of the Auto Trigger System.

-

-

The following supply voltage is used for a special purpose:

+12 V*

This voltage comes directly from the +12 V regulator U41and will be
present as soon as the power cord is connected, regardless of the po
sition ofthe ON/STANDBY switch. It is used for the ON/STANDBY
control logic and for supplying an optional OCXO in STANDBY to
avoid the long warm-up time otherwise needed to obtain maximum
accuracy.

At stand-by, the four main supply voltages are switched off, but as
described above, some parts of the instrument should not be
diconnected. Therefore the power module will never be switched off.
The PM6685 has consequently only a secondary power switch.

A relay (K5) disconnects the load on the +5 V and –5.2 V at stand-by.
Because the power module must always have a load on the regulated
voltage, seven bleeder resistors R149-R155 are always connected to
+5 V via J15. At stand-by the counter only needs +15 V, so a dummy
load consisting of R130-R145 is connected to the power module by
means of the relay K5 in order to stabilize the operation of the
switchmode converter.

+5 V controls the switching on/off of +12 V and +7 V. When +5 V is
on, Q6 and Q5 will conduct, i.e. +12 V will be on. If there is no +5 V,
Q6 and Q5 will be off, thus blocking the +12 V.

The ON/STANDBY logic controls relay K5, which operates as de
scribed above. It is also possible to open the relay by changing the
position of J16.

The ON/STANDBY logic consists of the RS (set-reset) flip-flop
U40B that is controlled by the ON/STANDBY button on the front
panel. Pressing STANDBY will apply a high voltage (+12 V) to the
set input. The inverting output of the flip-flop will be low, discon
necting K5 via Q14. Pressing ON will give a high voltage (+12 V) on
the reset input. The inverting output of the flip-flop will be high,
engaging K5. Inserting the power cord into the power inlet will cause
a pulse on the reset input, via C35. The microcomputer can disable
the ON/STAND-BY button via Q12 and Q7. This is done in remote
mode and during RAM-testing. A high level on the base of Q12 en
ables STAND-BY, a low level disables it.

The STAND-BY indicator on the front panel is controlled by the
+5 V via Q16. +5 V off lights the STAND-BY LED that is fed by the
uninterruptible +12 V*.

+5 V also indirectly controls the fan in the PM6685R. It is a 12 V DC
fan that operates only if +12 V is on. An NTC resistor, serving as a

OSC

The oscillator block generates, selects, and distributes the reference
clock for the circuit. The active semiconductors of the standard oscil

-

lator are included in this block. The crystal is connected to pins X1
and X2. A TCXO or OCXO is connected to X2 only. An external ref
erence clock is connected to EXTREF. The PWM signal generated at
OTRIM controls the frequency of the reference oscillator after exter
nal integration.

-

-

-

PG

A built-in pulse generator having the 10 MHz clock as a reference
can generate pulses with controllable duration and repetition rate at
the OUTPUT connector. The level is fixed TTL.

RTC

A real time clock not used at present.

TLDAC

This block contains two 10-bit DAC’s generating the trigger levels
for the input comparators, VOUTA for channel A and VOUTB for
channel B. An external reference voltage is connected to V+REFA
and V+REFB.

HO

The Hold Off block can manipulate the internal measuring signal X

-

-

-

in several ways. One operating mode simulates a low pass filter (nor
mal hold off), another mode is used in burst measurements.

The following blocks (SYNC, STST, CNTS and MCTRL) form the
actual measuring logic in the ASIC. Three types of measurements
can be made in this MEAS block:

Continuous measurements (frequency, ratio and period average).
Not used at present.

Controlled measurements (time interval, period single, pulse width,
frequency, totalize gated, totalize start-stop, and ratio).

Totalize manual.

SYNC

The SYNC block synchronizes the actual measurement with certain
internal or external events like measuring time and arming signals.

-

STST

The start and/or the stop of the measurements are controlled by this
block. External events can be used to define the exact moments.

4-10 Hardware Functional Description

EXTC

BURST

TRA
TRB

VCCO
GNDD1
GNDD2
GNDD3
GNDD4

GET

SB
SA

OKD

CLOCK

RE S ET

Inter-

polator

FNb

FNa

I

I

CY 1
CY 2

VC CG
GNDG
VR EFA D

IR ES
IN TP1
IN TP2

IN TS1

OK a

OKb

IN TS2

A2

A

SR

B

B2

P

MUX HO SYNC CNTS

X
Y

HODLYX
HODLYY

CL O C K

S TAAR M
STO ARM

STAD LY

STO DL Y

TI ME
MREF
FREQC
MCLK
PGARM

PCL

PGT RIG

X
Y

HODLYX
HODLYY

HO S X
HO S Y

XH
YH

XH
YH

CLOCK
ST O P

ST AR T

HO S X
HO S Y

STA AR M
STO A RM

STA DLY
STO DL Y
GET
TOTSTA
STA

TOTSTA

GATEO

STOP

STAR T

STST

STA

R1
R2

L1
L2

R1
R2
L1
L2

I

INTB
INTA

NB

FND

F

OKA

FNC

OKB

FNA

I

OK C

I

I

X1
X2

V+R EFO

OTRIM

V- REF O

EXTREF

MTC XO
IN TR EF

OUTMUX

MPCL K

PH1

PH2
VCCB
GNDB
VCCC

GNDC

GNDA
VCCA
VCCX +5

OSC

RTC

+5

PGOUT

TI ME

MREF

FREQC

MCL K

PGR EF

PG

PGR EF

PGT RIG

PGA RM

PGOUT

PG

Fig. 4-11 Counter ASIC, block diagram.

CNTS

Two 32-bit binary counters count external events or keep track of the
time.

Interpolator

This block is not used at present.

MCTRL

The different events in the measurement cycle of the ASIC are timed
by this block.

MPI

This is the microprocessor interface block. The bus width is 16 bits,
AD0 toAD15. Interruptsto themicroprocessor are generated at INT.

GET

The GET signal from an optional GPIB interface can control the start
of a measurement.

External Interpolator

n

The X-POLATOR unit is connected directly to the internal
interpolator in the ASIC. It is used for increasing the time resolution
beyond the limits set by the reference clock period of 100 ns. An er
ror pulse is generated in the SYNC block. Its width is determined by
the difference between an external event on an input channel and the
next clock pulse. This pulse controls a current generator charging a
capacitor. When the pulse has expired the voltage across the capaci
tor is A/D converted and the value is added to the result. There are
two interpolators, one for the start event and one for the stop event.

RTC

RTC

RTCX1

-

-

MCTRL

FI N1

DMAR

TLDAC

DMABR

CS RS SS

PCL

OK

MCL K

MPI

C1

C3

CS

A16

A18

ALE

VBAT

RTCX2

LARMN

RDN

AD0-AD15

A17

WR L N

WRHN

INT

A19

S1N

HO L D N

S2N

HLDAN

QDM AN

C2

S4N

S5N

S3N

FIN
MTIM E

V+R EFA
VOU TA
V- REF A
V+R EFB
VOU TB
V- REF B
VC CE
GNDE

VC CF
GNDF

C4

They are calibrated over the possible error pulse range to allow for
any aberrations from the theoretical linear behavior.

Oscillator Circuits

CPU Oscillator

n

The microcontroller U11 is clocked at 12 MHz. The crystal B1 is
connected to the XTAL inputs of the microcontroller.

n

Reference Oscillators

A 10 MHz crystal oscillator is used as the reference for the measur
ing logic. If a stable external 10 MHz reference is available, it can be
connected to REF IN on the rear panel and selected by means of the
EXT REF button on the front panel.

In addition to the standard crystal oscillator there are two optional
oven-controlled crystal oscillators (OCXO) to choose from.

Standard

The uncompensated standard oscillator consists of the crystal B2,
C109, C113-C115, R209 and R211. C115 is used for manual adjust
ment of the frequency when the calibration tolerance has been ex
ceeded. Theactive circuitryis builtinto theASIC U29and is accessi
ble via the pins marked X1 and X2.

OCXO

If one of the OCXOs is mounted, the standard oscillator has to be in
activated by moving the jumpers J23 and J25 to their alternative po
sition. These oscillators are connected to J24 and are self-contained

-

-

-

-

-

-

Hardware Functional Description 4-11

units with facilities for coarse and fine adjustment. They are fixed to
the main PCB with two screws. The output signal is AC-coupled to
the X2 pin on U29 via C107.

External

This input consists of an AC-coupled line receiver with Schmitt trig
ger function (U28) and is protected against excessive voltage
excursions by a resistor-diode network. The output signal from U28
has CMOS logic levels and is connected to the EXTREF pin on the
counter ASIC U29.

Logic

Microcomputer Circuits

n

Microcontroller

The microcomputer circuitry consists mainly of the microcontroller
U11, an Intel 16-bit CMOS 80C196, RAM (U22A), and EPROM
(U23A). The microcontroller is clocked at 12MHz. The data and ad
dress lines AD0 to AD15 are shared by means of multiplexing.
Therefore the addresses are stored in the latches U16A and U17A.
The ALE signal (Address Latch Enable) enables the latches.

UVEPROM

The main program is stored in U23A that is mounted in an IC socket,
making it easy to update and customize the instrument firmware by
changing the EPROM.

EEPROM

Front panel settings, GPIB address and certain other data that are not
changed frequently, e.g. information in the Protected User Data
Area, are stored in U12A which does not need battery backup.

Reset Circuit

A special reset circuit, the power supply supervisor U10, is included
in the design. If the +5 V supply line becomes lower than 4.5 V, the
reset output pin 5 goes low and the microcontroller will start over.
The length of the reset pulse is set by C88; 2.2 µF gives a pulse of ap
proximately 30 ms. U10 also controls the reset pulse during
power-up so that the microcontroller will be initiated correctly.

Keyboard Scanning

n

Main Board Keyboard & Display

U11

-

AD0-AD7 H0-H3

CPU

P1.0

HS1.0

P1.1

-

U13A

Latch

U14A
Latch

AD0-AD7

Board

V0-V7

LOCAL/PRESET

SCL
SDA

Fig. 4-13 Keyboard scanning.

The keyboard scanning is done in two modes. The first mode is ac
tive aslong asno buttonhas beendetected asdepressed. Then all out

-

­puts of U13A are set high, and the latch U14A is read. If no button
has been depressed, all outputs are low. This check is done at every
timer interrupt in the microcontroller, every 25 ms. If a button is
depressed, one of the output bits is high. When this event is detected,
mode two is entered. The outputs of U13A must be set high one after
the other to find the specific button. When found, only this button
will be checked, so other simultaneously depressed buttons will not
be recognized. The depressed button must stay down for several
timer interrupts before action is taken. After the button has been rec

­ognized, the timer interrupt SW will be waiting for the button to be
released. The button must be released for several timer interrupts be

-

fore the keyboard scanning returns to mode 1. Then the search for

-

other activated buttons can be resumed.

The following three buttons are not scanned in this way:

The ON button is connected to the ON/STANDBY logic in the

–

power supply.

CPU Latch

Key-

board

Latch

rd

GPIB

Fig. 4-12 Microcomputer circuits, block diagram.

4-12 Hardware Functional Description

RAM

Address Bus

UV

EPROM

OM

Address & Data Bus

2

ICBus

EE

PROM

Counter

ASIC

LCD

Drivers

LCD

The STAND-BY button is connected to the ON/STANDBY

–

logic in the power supply.

The LOCAL/PRESET button is connected directly to input pin

–

24 on the microcontroller U11. Pressing this button sends an
interrupt to a special handler in the SW.

Rear Panel Unit

The rear panel contains the following connectors

INPUTS:

External reference input D - REF IN (BNC)

–

External arming input E - EXT ARM (BNC)

–

Power supply inlet including EMI filter

–

OUTPUTS:

Internal reference output G - 10 MHz OUT (BNC)

–

If a GPIB interface is installed in the device, it is mounted on the rear
panel and connected to the main board with a flat cable.

Besides the normal standard GPIB connector, this optional unit also
has a BNC connector capable of outputting an analog representation
of any three consecutive digits on the display.

There is also a 6 SPST DIP switch on this unit for setting the default
GPIB address.

ON

ANALOG OUT

P M962 1
P M962 3
P M962 4
P M962 5

OF F

168 421
A DDRE S S

I E E E 4 88 / I E C 62 5 IN T ER F A C E
SH 1, AH1, T 5, L4, SR1,

RL1, DC1, DT 1, E 2

PM9626
PM9678
PM9690
PM9691

10M Hz O UT RE F I N E XT AR M

GDE

PM9628 /85
P M9697
_______
_______

EXT SUPPLY

12-24V DC

-I NT -S T BY
BAT T ERY

-EX T /L I NE

POWE R

90 V - 26 5V

PRIMARY FUSE

1.6AT

INSIDE

Fig. 4-14 Rear panel.

Hardware Functional Description 4-13