HP 456A Service and user manual

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5

AC

CURRENT

SERIALS PREFIXED:

PROBE

103-

,

OPERATING AND SERVICING MANUAL

PRINTED

3/61

00395-1

OPERATING AND SERVICING MANUAL

MODEL

SERIALS

PREFIXED:

456A

103

-

AC CURRENT PROBE

00395.1

HEWLETT-PACKARD

Mall

ROAD.

P&Lo

ALIO.

COMPANY

CALIFORNIA,

1961

".I.*.

Printed:

MAR

1961

Model 456A Table

of

List

Illustrations and Tables

of

Contents

Section

I

GENERAL INFORMATION

1-1

.

General Description

1.2 . Power Requirements

I1 OPERATING INSTRUCTIONS

2.1

.

General

2.2 . Operating Instructions

2.3 . Operating the Probe

.

Increasing the Sensitivity

2.4

.

Measurement Precautions

2.5 2-6 . Special Measuring Techniques

Ill

THEORY

3.1 . Introduction

3.2 . Probe Head

3.3 . Amplifier

OF

Title

................

OPERATION

.............

..............

TABLE

Page

.........

.......

........

.........

......

.....

.........

1-1 1-1 1-2

2-1 2-1 2-1 2-1 2-1 2-1

...

2-4

3-1

3-1 3-1

OF

CONTENTS

Section IV MAINTENANCE

V

Title

...............

4.1

.

General

.

Cabinet Removal

4.2

4.3

.

Operation on 230

4.4

.

Checking the Batteries

4.5

.

Replacing the Batteries

4.6

.

Converting to AC-Operated Model

.

Test

4.7

4.8

.

Front Panel Performance Check

.

Trouble Localization

4.9

4.10

.

Semi-Conductor Replacement

4.11

.

Calibration

.

4.12

4.13 . Replacing the Probe Cable

REPLACEABLE PARTS

5.1

5.2

5.3

Frequency Response

.

Introduction

.

Table

.

Ordering Information

................

...........

Volt

AC

........

.......

Equipment Required

.........

..............

........

..........

..............

of

Replaceable Parts

........

Page

4-1 4-1 4-1

......

.......

....

.....

. .

4-1 4-1 4-1 4-3 4-3 4-3 4-3 4-4 4-4

4-4

5-1 5-1 5-1

5-1

LIST

OF

ILLUSTRATIONS

Number Title Page Number Title Page

General Arrangement

1.1

.

Model 456A AC Current Probe

1.2

.

Typical Change

1.3

.

with Load Capacitance

Probe used with @ Model 302A

2.1

.

Operation 2-2

2.2

.

Cleaning Probe

2.3

.

Illustrating Development

2.4

.

Ground Loops

2.5

.

Illustrating Directional Effect

Current Measurement

Number Title Page Number Title Page

1.1

.

Specifications

.................

...............

of

Model 456A

. .

......

in

Frequency Response

.........

.....

Jaws

...........

of

.............

of

.........

1-1

1-2

2-1

2-3

2-4 4.4

LIST

OF

1-0

TABLES

Bucking Out Capacitive Component

2.6

.

of

Plate Current

Equivalent Circuit

3.1

.

Feedback Circuit

3.2

.

Servicing Etched Circuit Boards

4.1

.

Calibration and Frequency Response

4.2

.

Exploded

4.3

.

Schematic Diagram Model 456A

.

4.1 . Replacement

View

............

.............

of

Probe Assembly

...............

2-5

3-1

.....

....

.....

...

4-0 4-2 4-5 4-6

4-4

1.2

.

00395-1

Instruments

for

use with 456A

....

1-1

.

Replaceable Parts

5.1

............

5-2

iii

Section Table

I

1-1

SENSITIVITY

Table

1

ma/ma f 1%

1-1.

Specifications

at 1 kc

Model 456A

FREQUENCY RESPONSE:

PULSE RESPONSE:

MAXIMUM

EFFECT OF DC CURRENT:

INPUT IMPEDANCE:

PROBE SHUNT CAPACITY

DISTORTION

EQUIVALENT INPUT NOISE:

OUTPUT IMPEDANCE:

INPUT:

AT

1

KC:

*2%.

100 Cps to 3 mc; +5%, 60 cps to 4 mc;

-3

dh at 25

Rise

second.

1

amp rms; 1.5 amp peak. 100 ma above 5 mc.

No appreciable effect up to 0.5 amp.

(Impedance added in 50 milliohms tance of

Approximately 4 pf added from

For 1/2 amp input at

For

Less than

220 ohms into load of not

cps

and greater than 20 mc.

time

is

less than 20 nanoseconds, sag

in

series

1-1/2

inches of hookup

10

ma input at least

50

pa rms (100 pa when ac powered).

at

1

kc. Approximately

less

on

sensitivity and distortion from dc current

series

with measured

with 0.05 ph. (This

wire.)

wire

to ground.

least

SO db down.

70

db down.

+1

volt dc component. Should work

than 100,000 ohms shunted by approximately 25 pf.

is

less

than 16% per milli-

wire

by probe.) Less than

is

approximately the induc-

POWER:

WEIGHT:

DIMENSIONS:

ACCESSORY AVAILABLE:

Two Mallory Battery CO. TR

#

1420-0005 and 1420-0006), battery life

AC power supply optional at extra cost, 115/230 volts +lo%, 50 to

1000 cps, approximately

Net 3 Ibs.

5 in. wide, 6 in. deep,

is

2

ft

cable

456A-95B AC Supply for field installation.

long and terminated with a dual banana plug.

1

watt.

1-1/2

233R

and one TR 234 batteries stock

is

approximately 400 hours.

in.

high. Probe cable

is

5

ft

long, output

1-0

00395-1

Model 456A

Section 1

Paragraph 1-1

SECTION

GENERAL INFORMATION

1-1.

GENERAL DESCRIPTION.

The Model 456A current.

used

loscope

It

together

(see

,Conductor

I

Figure 1-1. General Arrangement of Model 456A

Current the Model 456A around the current carrying conductor.

is

an instrument for measuring ac

consists of a probe and amplifier, and

with

an associated voltmeter or oscil-

figure

measured

1-1).

by

merely clamping

the

probe

is

of

I

The

probe operates with an accompanying small ampli-

fier

to convert the portional voltage. The current-to-voltage conversion factor through directly from or oscilloscope. Table 1-2

which

is

1

the

can

be

Table 1-2. Instruments for

Voltmeters

400D 400H 400L 403A

Wave Analyzer

302A

ac

current beingmeasured to a pro-

millivolt output for 1 milliampere flowing probe. Current readings can thus

the

voltage calibrations

used

with

456A AC Current Probe

is

a list

the probe.

on

of

Oscilloscopes

he

taken

the voltmeter

instruments

use

with

120A

122A 130B 150A

1608

170A

00395-1

Figure

1-2.

Model 456A AC Current Probe

1-1

Section

1

Paragraph 1-2 For

flat

of

frequency response the shunt input impedance

the associated voltmeter

or

oscilloscope should be

greater than l00K ohms in parallel with 25 pf or

to

made to appear that value

the 456A.

of this requirement.

MENT

WITH

RECTIFIER TYPE METERS. The

loading in this type

may affect the reading.

DO

NOT USE THIS INSTRU-

of

instrument

is

Model 456A

excessive and

Lower shunt resistance will change the accuracy

at

all

equally pedance (about 200 ohms)

Different shunt capacitances have no effect

frequencies, due to the low output im-

of

the Model 456A.

on

the low

frequency response, but can affect the high frequency

as

gain

shown in figure

-6

1 MC

Figure

1-3.

10 MC

30 MC

Typical Change in Frequency

Response with Load Capacitance

The Model 456A output contains a dc component of approximately cessively Almost

(less

all

vdc which must not be loaded

than 10Kohms shunt load is excessive).

ac

voltmeters and oscilloscopes have

ex-

+1

dc blocking capacitor in the input circuit to take care

1-2.

The Model 456A

powered

POWER REQUIREMENTS.

is

available either as a battery

or

ac powered instrument. The

AC

Power Supply(@ stock #456A-95B) fits into the space normally occupied by the battery supply and takes the

of

place

it electrically. The

ac

power supply must

he ordered separately. When the 456A

teries

used

it

in

the field with battery operated voltmeters, such as the Model 403A AC Voltmeter, powered oscilloscopes. Battery operation useful in the laboratory where complete isolation

is

independent

powered with

of

power lines.

its

own internal bat-

It

or

may be battery

is

also

is

desired. While battery operated the 456A may be used with the chassis off ground without difficulty. This type

operation may also be desired

to

isolate

of

power line hum in a system where several instruments are used.

When the 456A chassis prong

is

in

is

used with the ac power supply the

automatically grounded through the third

the power plug. The three conductor power

cable supplied with the instrument is terminated in

a

polarized,

three-prong male

connector recommended

by the National Electrical Manufacturers’ Association

The

(NEMA). chassis for protection

third conductor grounds the instrument

of

the operating personnel.

WARNING

a

When using a three-prong to two-prong adapter

wire)

ground the third lead (green

externally.

1-2

00395-1

Model 456A

Paragraphs

Section 11

2-2

to 2-5

SECTION

OPERATING INSTRUCTIONS

2-1.

The Model 456A must or an oscilloscope.

Connect cable to

range. milliamperes in. millivolts the expected milliamperes being measured. The current range of the Model 456A

1

Vacuum Tube Voltmeter as ing input jack.

The spacing of the pins on the OUTPUT cable fits all

scopes (when used with AC-76A adapter). See table

clipping.

The Model 456A may

current, even below the noise

some provision

particularly

GENERAL.

be

used with an ac voltmeter

2-2.

Figure

OPERATING INSTRUCTIONS.

the

shielded plug of the Model 456A OUTPUT

a

voltmeter or oscilloscope of appropriate

The conversion ratio

2-2

shows a typical setup.

is

millivolts out equals

Thus the voltmeter should read in

is

less

than

milliampere to 1 ampere. The

is

ideal for this measurement

it

covers the entire range and has a

Model

3/4

400D/H/L

inch spac-

WARNING

DO NOT PLUG THE OUTPUT CABLE OF THE 456A lNTO A SOURCE VOLTAGE. Doing

so

will

OF

burn

out the tran-

AC OR DC

sistors and perhaps other components.

standard

connectors, such

as

on

Hewlett-

3/4

inch

Packard voltmeters, wave-analyzers, and oscillo1-2

for a list of

for use with

Hewlett-Packard instruments

the

Model 456A.

suitable

The Model 400D has an additional output terminal for viewing the voltage being measured with an loscope. This may measuring

the current at which a transistor

Model 302A Wave Analyzer

if

signal source

Transistor

(see

under

be

very useful, for example,

be

used

to measure

level

is

made to

filter

out the noise. The

is

ideal for this purpose,

the BFO of the 302A

figure 2-1).

test

-hp-

WAVE ANALYZER

of the probe,

is

302A

oscil-

starts

very

low

used as the

if

II

In this manner, currents even below 10 microamperes can be measured.

2-3.

The probe jaws may be operated withonehand. While holding the probe handle in the palm, squeeze the flanges together with open the jaws. Move the probe to the vicinity of the insulated flanges until the

Clip the probe over the probe in the direction

for a positive-going output signal. This procedure

important when using an oscilloscope but it may also

be

metrical waveforms with half-wave rectifier meters. All Hewlett-Packard meters listed

are

same reading whichever way the probe the the readings may tation of the meter and not a fault of the Model 456A.

Refer

meter or change

2-4.

Sensitivity of the Model 456A may be increased by looping the through the meter or oscilloscope of times that the current passes through the jaws. To obtain the by the number

series

measured number of into account

OPERATING THE PROBE.

the

fingers. This action

wire

being measured and slowly release the

jaws

fit over the

wire.

will

CAUTION

Do NOT let the jaws snap closed

as

they may

he damaged.

wire

with the arrow on the

of

conventional current flow

is

important when using this probe tomeasure unsym-

type

in

table

full-wave

wire.

to the Operating and Servicing Manual for the

INCREASING THE SENSITIVITY.

wire

jaws

true

loading

is

turns.

(see

rectifier

types

so

you

is

will

get the

clipped over

However, with half-wave type meters

be

different. This action

to

one of the recommended meters.

carrying the

current

more than once. The reading

will

he multiplied by the number

is a limi-

to be measured

on

the

reading divide the current indication

of

turns enclosed by the jaws. The

effect

of the probe on the circuit being

then multiplied by the square of the

This effect may have to be taken

paragraph 2-5D).

-hp-

456A

CURRENT PROBE

Figure

2-1.

Probe can

he

used with 302A

to measure distortion in current waveforms

or to measure small audio current,

described in text

00395-1

BFO

20

as

OUTPUT

-50KC

2-5.

Best performance will

MEASUREMENT PRECAUTIONS.

be

achieved by observing the

following precautions:

A.

PROBE HANDLlNG

1)

not snap the jaws closed by letting go of the

Do probe flanges abruptly. This action may damage the shield or the jaws.

2)

Do not drop the probe. The jaws are made from an

2-1

Section 11 Figure

2-2

Model

456A

INSULATED CONDUCTOR

BEING MEASURE0

1. Connect output of

456A

to a voltmeter or oscil-

loscope.

2.

Clip probe around by

squeezing flanges

3.

Connect ground-clip to instrument under test,

if

necessary

(see

wire

under test (open jaws

on

probe together).

paragraph

2-5E).

4.

Read current being measuredon meter or loscope (read millivolts as milliamperes).

5.

Note direction

of

arrow on probe. Conventional current flow in direction of arrow gives positive going output voltage.

oscil-

2-2

Figure

2-2.

Operation

00395-1

Model 456A

Section 11

Paragraph 2-5 (Cont’d)

Figure 2-3. Cleaning Probe

alkyd material which

is

but

3)

dirty

the jaws

not made to withstand the shock of dropping.

Keep

the probe jaws

or

if

the low frequency responsedropsoff, clean

as

shown in figure

chloride and the

is

very

durable in normal use,

clean.

brush

provided or, in extrerne cases,

If

the jaws appear

2-3

using carbon tetra-

a pencil eraser. The probe jaws should mate perfectly with

between

the

ferrite pole pieces. Foreign matter (dirt

no

air gap

specks, wax from capacitors, sand particles, pieces of insulating tape etc.) may hold the pole pieces from closing perfectly. Normally the only effect will he

to lower the gain at low frequencies (below 10 kc).

as

Even as small an air gap

the

gain significantly at low frequencies.

4)

Always clip

the

probe around insulated

0.0005 inch will lower

wire.

If

you must measure the current in a bare wire, first

wire

insulate the

5)

Do not expose the probe to high temperatures.

Exposure to temperatures above 55oC

with tape or insulating tubing.

is

not recom-

mended.

B.

DlRECT CURRENT IN THE SIGNAL BElNG

MEASURED. measured should preferably Direct current below that value will have

Direct

current

be

kept

in

the signal being

below 1/2 ampere.

no

effect

on

the measurement. C. ALTERNATING CURRENT FIELDS. The probe

is

shielded against external ac magnetic and electric fields. Extremely strong fields may cause an erroneous reading.

If

a strong ac magnetic field

Jaws

is

suspected, rotate the empty probe head with the

If

jaws closed.

the reading changes, an ac field

affecting the probe.

D.

GROUND

ground loops between the third prong on the indicating instrument. An ing for ground loops

LOOPS.

in

With

the

ac supply avoid

test setups, such as those produced

on

the

ac

cable and the ground

easy

method of test-

is

to clip the probe over the 456A output cable. Any reading indicates the presence of ground loops.

OTHER

EQUIPMENT

POWER

I

LINES

I

SET-UP

BEING

TESTED

I_--

POWER

Figure 2-4. Illustrating Development

Ground Loops

Referring to figure 2-4, note that the leakage current I-leakage causes a voltage drop across the groundlead resistance This appears as dition to the signal voltage, between the ac current probe of minimizing this problem ments to the same

Z1

and the indicating device Z2.

ac

receptacle. Another method

to

use

a battery-powered Model 456A.

is

a

voltage,

An

to connect both instru-

is

--

*

LINE

of

in

ad-

easy way

is

00395-1

2-3

Section

II

Paragraph 2-6

Model 456A

E.

EFFECT OF

MEASURED. The probe adds an inductance less than 0.05 microhenries With almost will

not

However,

all

affect the measurement.

if

the measurement

capacitance and very high impedance

PROBE

ON

CIRCUlT

BEING

of

to

the circuit under

test.

conditions this small an inductance

is

made in a very low

circuit,

with high ac voltages, and at high frequencies, the shunt capacitance of the probe to ground must be taken into

is

consideration. A capacitance

wire

ured when the probe

to the grounded shieldinside the

is

clamped around the wire. This

capacitance typically has

added from the meas-

456A

a

value anywhere from 1 pf

probe

to 5 pf, depending upon wire size, insulation and location within the probe aperture. This capacitance has two effects:

1)

The measured

capacitance

to

2) The capacitive current which

wire

ground

is

slightly “loaded” with

of

around 3 pf.

flows

to

a

ground through this wire-to-probe capacitance can be measured by the probe, although

a

negligible amount to the reading of the actual cur-

it

almost always adds

rent in the wire.

To

test

if this effect should he considered, solder one

end

of

a short, stiff, piece circuit at the point where the measurement made. Leave the other end This

wire

will

have voltage on it but it. Clip the probe over this Reverse the direction that the probe wire

(point arrow

meter again.

on

probe in other direction) and read

If

there either of these positions the probe capacitance has effect.

If

there

is

a reading proceed to the next

is

of

insulated

of

this wire unconnected.

no

wire

and read the meter.

no

reading

wire

current through

is

clipped on the

on

the meter in

to the

is

to be

no

paragraph.

THE PROBE AND HAS AN EQUIVALENT CIRCUIT

THIS CURRENT THIS CURRENT

MEASURED

/-

I

WIRE

BEING MEASURED

To

OF:

5pF

NOT

MEASURED

\

RO

PROBE MEASURES CURRENT IN CIRCUIT ON THE SAME SIDE

OF

ARROW,

Figure

2-5.

of

1)

Ground oscilloscope

as

ground with

short leads

2) Connect special resistive ground

to the closest ground to theconductor being measured.

4) Ground 456A to oscilloscope standard (non-resistive) short clip lead (not furnished).

OF

PROBE AS SIDE

Illustrating Directional Effect

Current Measurement

or

voltmeter

as

possible.

to

lead

or

voltmeter with

equipment

(supplied)

a

I’

I

,

The shunt capacitance introduced by the probe

5

pf (typically 3 pf). Assuming the worst case

5

pf, a maximum error current

I

=

0.03 ma X volts X megacycles

can flow through the 5 pf

1

voltage of

volt impressed across this shunt capaci-

tance will cause a reading

456A.

However, at higher frequencies the effect will

of:

to

ground. That is,

of

only 0.03 ma by the

is

1

to of

a

1

mc

increase proportionally. Even with this effect you may choose which side of the

circuit to measure the current. See figure 2-5.

Note

in

figure 2-5 the probe measures the current

in

flowing

of

side

the circuit on the same side

the arrow

on

the probe.

Occasionally at high frequencies (above greatly magnified voltage effect exists

is

frequency. This effect

caused by a resonance be-

at

as

a

the wide

15

mc)

particular

tween excessive external ground lead lengths and

stray capacities. The following steps are suggested

of

to eliminate this type

problem:

2-4

2-6.

Since the probe

it

instantaneous value

SPECIAL MEASURING TECHNIQUES.

is

effectively a current transformer,

has the property that

it

will algebraically sum the

of

the currents in two

or

more

conductors it may be clipped around. This property

a

makes the probe in applications in which balance ac currents. amplifier shown in figure 2-6

valuable and easily-applied tool

it

is

desired to equalize

For

example, in the class C

it

is

possible to use

or

this summing property to examine the plate current

of

pulses exclusive through the capacity

will

allow you

to

the current component flowing

of

measure the true angle

the tube. This arrangement

of

conduction

of the class C amplifier. The method used to obtain the bucking current

was

cated in figure 2-6. The probe

of

a

from an external variable capacitor was connected to

the plate lead

the tube, but at the same time a lead

clipped around

the plate lead and passed through the probe By suitably adjusting the variable capacitor,

to

citive current equal

but in opposite phase to

as

is

indi-

shown.

a

capa-

the

capacitive current flowing at the plate can be applied

to

the probe.

00395-1

Model

456A

Paragraph

Section 11

2-6

(Cont’d)

Note that

ure

of

the

because should

be

this

arrangement provides a dynamic meas- The probe

output capacity of

the

final setting of

equal to the

tube

the

tube.

the

variable capacitor these are equalizing

output capacity.

Figure

This occurs equalizing applications. Especially common among

2-6.

Bucking Out Capacitive

Component

of

Plate Current

is

valuable

in

the

a number

input

push-pull and balanced circuits tube applications.

of

other

current-

and output currents

in

both transistor and

in

00395-1

2-5/2-6

Model 456A

Section III

Paragraphs 3-1 to 3-3

SECTION

THEORY

3-1.

The Model 456A consists of a probe and an amplifier. Current to a current in the probe which

wire.

3-2.

The probe head acts as a 400:l step-down current transformer. That

wire

The output of the probe drives the amplifier.

3-3.

The amplifier consists of a common-base circuit driving a common-emitter output stage. transistor the second transistor Referring to the schematic you will signal from the prohe

INTRODUCTlON.

be

measured flowing through a wireinduces

This

current

PROBE HEAD.

around which the probe

of

1/400th

tor C2 to the emitter of

1

AMPLIFIER.

is

is,

milliampere into the probe secondary.

used for impedance transformation and

is

clamped around the

then amplified

1

milliampere flowing in the

is

used as a current amplifier.

is

fed through coupling capaci-

in

the amplifier.

is

clamped will induce

see

that the ac

QI.

The

OF

first

III

OPERATION

The

equivalent circuit

figure 3-1. where

sistor.

shown.

to

is

Referring to figure 3-2 note that the input current applied to should work into zero resistance for best frequency response. sistance still further.

Note that the current applied to

slightly less than the current flowing

R8

of Q2 amplifies and inverts the signal and feeds to

The transistors have internal resistances

Emitter

this

discussion, while the collector resistance

so

large that

times

less

and

Q2

so

re

through

as

rc

most

it

While this resistanceis small the

re.

So

it

large to

than unity, the current flowing out will be

have resistance much higher than the Zin

of

thecurrentis fed into

R12, 9 and 10.

FEEDBACK

can

be thought of as shown in

is

the current gain of the tran-

resistance

may be neglected.

is

desirable to lower the input

flow

re

is

small,

re

out

of the transistor. Since

but

causes a current

in.

Q2.

A

relevant

Resistors

Transistor

it

as

rc

is

probe

re-

back

The first transistor Q1

fier

to match the low impedance of the probe to the

higher impedance of transistor

is

connected in a common-base configuration input impedance and high output impedance. Even though the current leaving Q1 the current going into

the

impedance level has been increased. Thus the signal that goes into current but at a higher impedance level.

The signal then goes through CR1,

back

furnishes

Q2.

Transistor

the

emitter

amount

of

a

better frequency response, lower input

diode that to the base of stage which amplifies and reverses the phase signal. This stage amplifies the current and feeds

back out-of-phase the emitter fed

A

large

back a signal 180' out-of-phase with the signal and

in

parallel with it. This parallel current feedback results in impedance, dc bias stability, lower distortion, etc.

is

used as an

Q2.

there

is

Q1,

Q1

comes out as a slightly smaller

an

bias for

Of

Q1

feedback

02.

Q2

is

through

The

Of

input

Transistor Q1

slightly

a

power gain since

8-volt breakdown

signal

a

common-emitter

Q1

less

is

The output

R12,

is

used

ampli-

for

low

than

applied

of

the

is

and

10.

to

feed

'e

Figure Equivalent Circuit in the

it

0

Figure

This current

tude almost enough to cancel out the original signal.

Thus

any

current voltage caused by the current from

input current the amount of voltage developed at the input

Since

nism explained previously, the impedance This resistance consisting of R12, 10and 9 is approxi-

mately 400 ohms and the output voltage

is

used to step-up voltage-to-current ratio 400 times.

The current in the amplifier has been reduced in the probe output voltage reduced current will exactly equal the number of milliamperesflowing

voltage developed

is

a

device

this

voltage

to

1/400th of the current being measured. The

wire

being measured.

3-2.

Feedback Circuit

is

fed back out-of-phase

cancelled by the

is

proportional

developed

is

used

is

developed. Thevalueof 400 ohms

is

made numerically 400 times this

so

that the millivolts at the output

I

and

across

is

re

by

out-of-phase

For constant

Q2.

to

its input

reduced

as

by

a load across which

SD-S-84

of ampli-

the

initial

impedance.

the

mecha-

is

lowered.

00395-1 3-1

Section Figure

IV

4-1

Model 456A

SERVICING ETCHED CIRCUIT BOARDS

Excessive soldering iron be cemented

A

break

Use only high quality rosin After soldering, clean off any excess flux and

heat

or pressure can lift the copper strip from the board. Avoid damage by using a low power

(50

watts maximum) and following these instructions. Copper that lifts

in

place with a quick drying acetate base cement having good electrical insulating properties.

in

the copper should be repaired by soldering a short length of tinned copper

core

solder when repairing etched circuit boards.

coat

the repaired area with a high quality electrical varnish

or lacquer. When replacing components with multiple mounting pins such

it

will

potentiometers,

it

is

until WARNING:

free.

If

be necessary to

the specific instructions outlined in the steps below regarding etched circuit boards without

lift

each pin slightly, working around the components several times

as

tube sockets, electrolytic capacitors, and

eyelets are not followed, extensive damage to the etched circuit hoard

1.

Apply

heat

sparingly

If

replaced.

an eyelet

ponent side not pass through an eyelet, apply heat to con-

-

ductor side

lead

in

thecircuit board, apply heat on com-

of

to

lead

of

component to be

of

component passes through

board.

If

lead ofcomponent

board.

2.

Reheat solder in vacant eyelet and quickly in-

sert

a

small does not have an eyelet, insert drill from conductor side of board.

wire

NEVER

will

result.

awl

to clean inside of hole.

off

the board should

across the break.

USE

PASTE

FLUX.

If

awl

or

hole

a

#57

3.

Bend clean tinned leads

fully insert through eyelets

In

the event that either the circuit board has been damaged

method shown below. This

Clip lead

This procedure

as

shown

is

used in the field only

below.

on

new part and care-

or

holes in board.

is

especially applicable for circuit boards without eyelets.

.-

HERE

as

an alternate means

4.

Hold part against board (avoid overheating) and solder leads. Apply heat to component leads correct side

or

the conventional method

2.

Bend protruding leads upward. Bend lead

of

board as explained in step

is

impractical, use

new component around protruding lead. Apply solder using a pair of long

nose

pliers

heat sink.

APPLY

SOLDER

of

repair. It

is

not used within the factory.

as

on

1.

of

a

Figure

4-1.

Servicing Etched Circuit Boards

00395-

1

Model 456A

Section

Paragraphs 4-1 to

IV

4-5

SECTION

MAINTENANCE

4-1. GENERAL.

The Model 456A should require very littlemaintenance.

It

is

built with etched circuit wiring and transistors

which should ensure long, trouble-free life. However,

care

should trouble occur special servicing to avoid damage to the transistors etched circuit board.

REPLACING TRANSISTORS. The transistors soldered

resorted are faulty. Unless extremecareis taken when soldering, the transistor may be damaged. See figure 4-1.

Components within instruments are conservatively

operated In Usually, the instrument must be immediately repaired with a minimum of

approach can greatly simplify and thereby speed up

the repair.

Specifications for the Model 456A AC Current Probe

are given give additional tests and the data they contain

to

Your Hewlett-Packard representative maintains complete facilities and specially trained personnel assist you with any engineering, application, tests, or repair problems you may have Packard instruments.

4-2.

The instrument may

removing the two

and pulling the cabinet loose from the front panel and

side

4-3.

The

ation unless otherwise specified. It can be quickly

and easily converted

in:

substitution of transistors should not

to

unless

Be

careful not transistors. Small bias changes may a transistor

Be

sure

soldering.

iron applied at the input may exceed ratings

on

the transistors at the output.

to

provide maximum instrument reliability.

spite of this, parts within an instrument may fail.

there

is

some indication that they

CAUTION

to

short voltages across the

due

to excessive dissipation,

to turn the unit

A

small leakage current from the

“down

in

table 1-1. Theproceduresin this manual

be considered as specifications.

CABINET REMOVAL.

CAUTlON

Remove power cord from receptacle

is

equipped with

frames.

OPERATION

Model 456A

ac

supply.

be

taken from the cabinet by

screws

is

at the rear of the instrument

ON

230

normally wired for 115 volt oper-

to

operate from a nominal line

must be taken in

off

before doing any

time”.

A

with

VOLT AC.

or

the

are

be

ruin

systematic

are

not

Hewlett-

if

unit

to

IV

voltage

50

remove the short

off

4-4.

Whenever trouble the BATTERY TEST terminals. below 7 volts replace all TERY TEST terminals are across only part of the batteries. he replaced of the batteries are depleted the remaining batteries are probably

the BATTERY TEST jacks could other battery could be depleted. countered, remove the cabinet and test the voltage

of

Discard battery

4-5.

Whenever the voltage at the BATTERY TEST terminals falls below 7 volts or pected, replace the batteries. Turn the instrument

OFF.

4-2. Remove and discard all batteries. Replace the batteries with one Mallory Type

of

either 115 or 230 volts and a frequency of

to 1000 cps. To convert for 230-volt operation

across

before doing any soldering.

CHECKING THE BATTERIES.

is

For

this reason all of the batteries should

if

the voltage

low

also. Inaddition, the batteries across

BT3 also. This voltage shouldbeat least 4.7 volts.

if

lower.

Mercury batteries generate hydrogen gas

the

end of their life orwhentheyare shorted. Hydrogen gas exploded by the heat of the battery. Observe the following precautions when using mercury batteries.

1)

Never

after its voltage falls voltage, or when it fails to operate the equipment in which it

Never

2) mercury cell battery.

3)

Never the equipment battery fails to operate

4)

Never

teries. Discard dead batteries

possible. Discard basket. to the explosive hazard, mercury vapor EXTREMELY TOXIC.

5)

Store spare mercury-cell batteries in cool, adequately ventilated area.

REPLACING THE BATTERIES.

Remove the cabinet as instructed

is

discharge a mercury-cell battery

place a direct short across a

leave the POWER switch ON when

retain exhausted

If

battery

R90.

Turn the instrument

encountered check the voltage at

If

this voltage

of

the batteries.

is

helow 7 volts.

be

WARNING

highly explosive and may be

below

70%

of

is

used.

is

not

in

use, or

the

equipment.

mercury-cell

in

garbage, NOT

is

incinerated.

DO

NOT INCINERATE.

The

BAT-

If

some

fresh while the

If

trouble

its

after

as

in

at

nominal

the

bat-

soon

as

waste

addition

is

en-

a

if

the batteries

TR

in

paragraph

234

battery or

are

sus-

is

00395-1

4-

1

Section

IV

Figure 4-2

Model 456A

Since

the

calibration and frequency response of

the

Model 456A accuracy of able for

this

termine easily only

with

wrong

1.

Connect probe to test the

wire

2. Set Model 650A to

is

usually much

the

best instruments generally avail-

test,

the purpose of

if

there

is

the Model 456A.

setup

through the probe jaws

1

KC and

range.

3.

Set

Model 400D/H/L to

4. Adjust AMPLITUDE control H/L reads exactly 0.1 volt.

better

this

test

than

is

to

the

de-

something radically

as shown, looping

ten

times.

on

the 3 VOLT

0.1

VOLT range.

on

650A until 400D/

456A

5.

Connect input Leave the

the

OUTPUT cable of the 456A to

of

the

400D/H/L

wires

in

place

still connected to the 470C.

of

the 470C.

the

6. Read 400D/H/L. Reading should he within sum of specifications of the 470C and 456A.

7. Repeat above steps with 650A quencies up to

100

kc.

or frequency response

set

at other

If

the

456A calibration

is

poorer than test ac-

fre-

curacy or specifications the probe may he bad.

However,

much poorer than the specifications way to test a probe process

since

the test accuracy

is

to repeat the above

with

another probe known to be good and

is

the

usually

best

compare results.

Figure 4-2.

Calibration and Frequency Response (approximate method)

4-2 00395-1

Model 456A

Section IV

Paragraphs 4-6 to 4-9

equivalent, and two Mallory Type

in

series.

WITH

THE BATTERY HOLDER. Note that the small termi-

on

nal dry cells.

BE SURE THE BATTERIES ARE MAKING CONTACT necessary, bend the battery holders make good contact. are used in around the batteries at the ends which meet in order to get good contact between them.

4-6.

The battery-operated model can be quickly and easily converted to an ac-powered model. Remove the instrument from the cabinet graph holder at the battery holder end. Remove the two

screws

the battery holder chassis and batteries, Substitute the ac power supply stock #456A-95B)

in

the

chassis.

Fasten the supply with the same the battery holder chassis. Solder the loose to the terminals (marked with the corresponding colors) on the hoard. Replace the cabinet.

BE SURE TO INSTALL THE BATTERIES

THE SAME POLARITlES

the battery

WITH

series

CONVERTING TO AC-OPERATED MODEL.

4-2.

Unsolder the

holding the battery holder chassis. Remove

space formerly occupied

is

negative not positive as with

THE BATTERY HOLDERS.

In

the holder where two batteries

cut off

part

wires

TR

233R

batteries

AS

MARKED ON

so

that they do

of

the cardboard tubing

as

instructed in para-

going to

by

the battery holder

screws

the

used

battery

if

to

GOOD

any.

mount

wires

If

Loops. any appreciable hum

2)

noise as read less than 75 u volts (100 u volts with ac-powered model).

(if

Check with 456A POWER switch off to

loops exist.

B.

Note that this test

readily available equipment. test accuracy will he much poorer than the probe deviation from specification. that the probe

4-9.

Adopting a systematic approach to troubleshooting

enable you to find the trouble in the shortest possible

time and eliminate the possibility of damaging the

transistors or other parts of the instrument. Whenever

trouble

the order given until the trouble

trouble has been located

1) given specifications proceed to next step.

Follow the procedure in that paragraph until

is

eliminated.

Turn on the 456A with

on

the meter

If

ac powered), or try replacing CR1, Q1, or

CALIBRATION Perform the procedure illustrated in figure

Perform the front-panel performance check

in

not check C94, power supply capacitor

If

they do,

is

within specifications.

TROUBLE LOCALIZATION.

is

suspected, perform the following steps in

paragraph 4-8.

no

input to the probe. The

or

oscilloscope should

see

if

ground

see

paragraph 2-5D.

AND

FREQUENCY RESPONSE.

used only for rough testing with

In

almost all cases the

In

this

case

assume

is

located. After the

proceed

If

to the next paragraph.

instrument does not meet

he

Q2.

4-2.

will

as

4-7.

The following Model 456A:

1)

such as Model 403A or 400H/L.

2)

3)

such as Model 470C.

4) 410B or 412A.

5) Variable Transformer continuously adjustable from meter accurate within

6) Clip-On Milliammeter, such

4-8.

Perform this check upon receiving this instrument or whenever trouble

A.

1)

and read the output

If

TEST EQUIPMENT REQUIRED.

test

equipment

Vacuum

Signal Generator with output to 4 mc, such as

Model 650A.

Shunt Resistor of 10 ohms accurate toatleast

Dc

NOISE.

To

Tube

voltmeter accurate to within

Vacuum

100

FRONT PANEL PERFORMANCE CHECK.

check ac-powered 456A turn instrument

Tube

Voltmeter, such as Models

to 130 volts, equipped with a monitor volt-

is

suspected.

noise

there

is

appreciable hum

is

required to

1

volt.

as

Model 428A.

on

anoscilloscopeor meter.

see

paragraph 2-5D. Ground

test

the

*l%,

off

2)

Clean probe jaws

and figure 2-3.

3)

If

instrument does not operate

tinuity of both cables with an ohmmeter. Check probe by substitution

4)

Check the voltage of the batteries as described

in

paragraph 4-4, Checking the Batteries. BATTERY TEST jacks on the front panel operated instrument, the voltage should be approximately the voltage is

5) Measure the current in the red (B+) lead running

around the front

milliammeter, such

Milliammeter.

If

6) going to switch. There should he in this lead. If there wrong in the amplifier (provided the supply voltages

are

7)

an ac voltmeter, such 400D/H/L), from any pink (B-) lead to any red (B+)

lead. because eliminating all ground loops

Refer

8

volts with an input of 115 volts ac.

is

faulty or the instrument

too high, check voltages across CR1,

Measure

correct).

Measure the ripple

to paragraph 2-5D for instructions concerning

This

current

is

as

described

if

another probe assembly

much below 8 volts, either the supply

is

of

the etched-circuit board with a

as

The

a

very difficult measurement to make

the Model 428A Clip-On

current

in

violet-white lead (ground)

is

more current, something

on

the ac supply hy connecting

as

the Model 403A

in

paragraph 2-5A3

at

all check con-

is

available.

At

the

of

an ac-

drawing too much current.

should be 5.5ma ma.

Q1,

and

92.

less

than

0.02

ma

is

(or

Model

is

necessary.

If

00395-1

4-3

Section Paragraph 4-10 to 4-13

IV

Model 456A

the elimination of ground loops. the ground loops, the ripple CR92 and Q90. Diode CR92 should have 14 volts

volts across it.

8)

If

the

instrument section trouble by measuring the voltages as shown schematic diagram.

CAUTlON

TAKE CARE NOT TO SHORT THE WIRING

WHEN TROUBLESHOOTING. EVEN A MOMENTARY SHORT MAY BURN OUT SISTOR

The transistors can be checked in a similar manner. Since the transistors used the pnp type the voltage at the emitter should be slightly positive (within 0.4 volt) of the voltage

base.

tive

with respect to the base and of the value shown

on

the

Unfortunately, due to the large amount of feedback

any trouble may cause all of the voltages to be off. First, try to find the trouble by resistance measure-

ments.

transistors and diode, and tester.

4-10. SEMI-CONDUCTOR REPLACEMENT.

Do

NOT replace the transistors

there are faulty, as you may damage them. Turn the in-

strument OFF before doing any soldering as ac leakage from the soldering iron may overload and damage the transistors. In addition

on

iron nosed pliers between the iron and semi-conductor. The pair heat helping to prevent damage to

Table

replacing the components.

OR

DIODE.

The voltage on the collector should be nega-

schematic diagram.

If

this fails you may have to remove the

is

a definite indication that these components

any semi-conductor lead, clip a pair

of

pliers

4-1

lists the tests which should be made after

will

act as a heat sink and absorb

If,

after eliminating

is

still too great check

is

faulty, locate the

A

TRAN-

in

this instrument are of

test

them

on

a simple dc

or

diodes unless

before

the

semi-conductor.

on

the

on

the

using an

of

long-

4-12. FREQUENCY RESPONSE.

Perform

4-13. REPLACING THE PROBE CABLE.

A. cable assembly a special cable terminated at one end

with a Microdot miniature connector and at the other

end with

nectors may be replaced but

a

new probe cable assembly, stock #456A-21A-8, be installed instead because of difficulties encountered in replacement.

cable under the handle this connector four new parts and for assembly

for the 425A-21B Microvolt Ammeter

instructions. C. CRIMP-ON GROUND CONNECTOR. This con-

quent melting of the cableinsulation. Crimp the ground lead

soldered, clamp insulation to act as a heat sink.

the procedure given in figure 4-2.

GENERAL. The cable assembly used 456A-21A Probe Assembly includes in the probe

a

crimp-on groundlead. Both of these con-

it

is

recommended that

MIDRODOT MlNlATURE CONNECTOR. The micrcdot connector terminates the end

(see

figure 4-3).

a

special hand tool

are

required. See the operating note

is

nector

on

again,

Component

CR1 CR90 CR91 CR92

Q1

crimped to avoid soldering and conse-

if

possible.

a

pair of pliers between the iron and

Table 4-1. Replacement

None Check power supply (par. 4-9) Check power supply (par. 4-9) Check power supply (par. 4-9) None

If

the ground lead must be

Test

To

Probe

in

of

the

replace

the

for

4-11. CALIBRATION.

Perform the procedure in figure 4-2 at 1 kc. Adjust

R9, Gain Set Potentiometer,

is

exactly

amperes input).

R7,

9, 10

4-4

0.1

volt (millivolts output equals milli-

If

you can’t reach calibration, check

and

12,

and the probe.

so

that the voltage out

Q2

Q90 Probe

Check calibration (par. 4-11) Check power supply (par. 4-9) Check Calibration (par.

check frequency response (par. 4-12:

4-11);

00395-1

Model

456A

INDIVIDUAL PARTS

NOT FIELD REPLACEABLE

SHOULD POINT AS SHOWN

PROBE CABLE

PROBE GROUND LEAD ASSEMBLY

Section

Figure

IV

4-3

Figure

4-3.

Exploded

View

of

Probe

Assembly

FRONT PANEL

OF INSTRUMENT

00395-1

4-5

Section

IV

Figure 4-4

PROBE

C5

.01 UF

Model 456A

300

AC

POWER

R93

R8

270

SUPPLY

4-6

Figure 4-4. Model 456A

AC

Current Probe

00395-1

Model 456A

Paragraphs

Section

5-1

to 5-3

V

SECTION

REPLACEABLE PARTS

5-1.

This

placement parts for the 456A AC Current Probe.

5-2.

Table 5-1 order of reference designators. At the end of the table are listed miscellaneous items such which have

Detailed information

is

ing to the part to appear designators applying to the same part initial designator. The detailed information includes the following:

4)

INTRODUCTION.

section contains information for ordering

TABLE OF REPLACEABLE PARTS.

lists

replaceable parts in alpha-numerical

as

no

assigned reference designators.

on

a part used more than once

listed opposite the first

1)

Full description of the part.

2)

Manufacturer of the part

see

appendix codes, List of Manufacturers.

3)

Total quantity used Recommended spare quantity for complete main-

tenance during one year

reference

in

the table. Other reference

in

the instrument (TQ

of

isolated

designator apply-

in

a

five

service

reference

digit code

(RS

column).

re-

knobs

the

--

column).

V

5-3.

To order a replacement part, address order or inquiry either to your authorized

or,

Specify the following information on a part:

1) Model and serial number

sure

2)

3) Circuit reference designator,

4) Description.

To

description of the part including its function and location

ORDERING INFORMATION.

@

sales

CUSTOMER SERVlCE Hewlett-Packard Company

395 Page Mill Road Palo Alto, California

in

Western

Hewlett-Packard

Rue du Vieux Billard

Geneva, Switzerland

to include the three-digit serial prefix.

@

stock number.

order a part not

in

Europe, to

the circuit.

S.

A.

No.

1

of

the instrument. Be

listed in table 5-1,

give a complete

office

or

to

Table 5-1. Replaceable Parts (Sheet

Ckt Ref.

BT1,2 BT 3

c1

c2

c3

c4, 5

C6

00395-1 5-

Battery, mercury cell: 4V, TR 233R Battery, mercury cell: 5. 33V, TR 234

Not assigned Capacitor: fixed, electrolytic,

200 pf -10%

Capacitor: fixed, electrolytic,

500 pf -10%

Capacitor: fixed, ceramic,

.Ol

pf

Capacitor: fixed, electrolytic,

10

pf

120%,

-10%

Description

+loo%,

3 vdcw

1000 vdcw

+loo%,

25 vdcw

See introduction

Mfr

*

37942 37942

56289

to

this section

1420-0005 1420-0006

0180-0060

0180-0063

0150-0012

0180-0059

Stock

1

No.

of

4)

2

1

Section

V

Model 456A

Ckt Ref.

c7

C8 thru C89

c90,

91

c92

c93 c94

CR1

CR2

thru

CR89

Table 5-1.

Description

Capacitor: fixed, ceramic,

pf

5 Optimum value selected Average value shown

Not

assigned

Capacitor: fixed, electrolytic,

40

uf

Capacitor: fixed, electrolytic,

100

pf

Same

as

Capacitor: fixed, electrolytic,

100 pf, 12 vdcw

Diode, silicon: breakdown Not assigned

500 vdcw

-15%

+loo%,

-10% +loo%, 15 vdcw

C6

50 vdcw

at

factory

Replaceable Parts (Sheet 2 of 4)

Mfr

*

96095

56289

28480

Stock

0150-0008

0180-0050

0180-0061

0180-0039

G-29A-17

No

RS

1

CR90, 91 CR92

J1

J2

P1

P2

thru

P89 P90

Q1,2 23 thru

Q89 Q90

31

thru

34

R5

Diode, germanium: 1N38A Diode, silicon

Connector, female: red Connector, female: black

Connector, male: output Not assigned

Cable, power

Transistor: 2N1516 Not assigned

Transistor: 2N650

Resistor: fixed,

24 ohms

Resistor: fixed, composition,

22

Part

Component not separately replaceable

+5%,

ohms

of Probe Ground

/

OC170

composition,

.lw

Lead

Assembly

08792

28480

00373 00373

24655

70903

73445

04713

01121

1910-0002

G-31A-15L

1251-0131 1251-0132

1250-0092

8120-0037

1850-0003

1850-0048

0674-0002

2

1

2

1

*See introduction to this section

5

-2

00395-1

.-

Model 456A

Ckt Ref.

R6

R7

R8

R9

R10

R11

R12

R13

Table 5-1.

Description

Resistor:

2.7

Resistor: fixed, composition,

3300 ohms

Resistor: fixed, composition,

2700

Resistor: variable, composition, linea

taper, 100

Resistor: fixed, composition,

100 ohms Same Resistor: fixed, deposited carbon,

392 ohms

Resistor: fixed, composition,

180 ohms Optimum value selected Average value shown

ohms

as

fixed,

R6

composition,

*lo%,

1/2

+lo%,

*lo%,

ohms

+lo%,

+1%,

*lo%,

+30%,

1/2

W

w

W

w

1/3

at

factory

W

Replaceable

Mfr

01121

11450

01121

19101

01121

Parts

*

(Sheet 3 of 4)

Stock No.

0699-0001

0681-3321

0681-2121

2

100-0108

0681-1011

0721-0301

0681-1811

'Qd

2

1

RS'

1

Section

V

R14

R15

thru

R89 R90

R91

R92

R93

R94

R95

s1

T1 thru T89

Resistor: fixed, composition,

1/2

W

2

W

1/2

W

2400 ohms +5%, 1/2

Not assigned

Resistor: fixed, composition,

15,000 ohms

Resistor: fixed, composition,

680

ohms

Resistor: fixed, composition,

10,000 ohms Resistor: fixed, composition,

ohms

6800 Resistor: fixed, deposited carbon,

4000 ohms

Resistor: fixed, deposited carbon,

2250 ohms

Switch, slide: DPDT Not assigned

*lo%,

+lo%,

*lo%,

*l%,

01121

19101

42190

0686-2425

0693-1531

0681-6811

0687-1031

0681-6821

0121-0132

0721-0120

3101-0011

1

T90

00395-1

Transformer, power

28480

*See introduction to this section

9100-0120

1

5-3

Section

V

Model 456A

Ckt

Ref.

Table 5-1.

Description

MISCELLANEOUS

Battery holder: 4 cell

6

of:

cell

ft.

long

Battery holder: Brush, nylon (electric razor Cable Assembly: output

consists Cable, delay line, 2

Plug,

male Connector, male Can, shield Boot, cable Spacer, standoff

brush)

Replaceable

Mfr

28480 28480

28480

99109 24655 24655 28480 28480 00866

Parts

*

(Sheet 4 of 4)

Stock

No.

G-64B

G-64C

8520-0017

456A-16A

8120-0048

1250-0091

1250-0092 4 56A- 5 5A 412A-83A 0380-0048

RS'

1

0

1

0

1

0

1

0

1

0

1

0

1

0

1

0

1

0

Lead, probe ground

includes

R5

28480

4 56A -2

lA

1

5-4

*See introduction to this section

00395-1