Hp 412a Service manual

I.

:

HP

Archive

..

.

This vintage Hewlett Packarddocument was

preserved and distributed by

www.

hparchive.com

'

Please visit us on the web

!

..

On-line curator: Tony Gerbic

I

i

(r,

,'

a

i

f

OPERATING

AND

SERVICE

MANUAL

(HP

PART

NO.

00412-90003)

MODEL

412A/AR

DC

VACUUM

TUSE

VOLTMETER

SERIALS

PREFIXED: 301-, 3160, 424-,

649-

Copyright Hewlett-Packard

Company

1961

P.

0.

Box

301,

Loveland,

Colorado,

80537

U.

S.A.

1

i

OOT29-5

Printod:

NOV

1968

I

0

Model

4

12A

h

TABLE

OF

CONTENTS

Section Page

I

GENERAL INFORMATION

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

1-1

1.1

.

Introduction

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

1-1

1.7

.

Specifications

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

I

-I

1.Y

.

instrument and Manual Identification

.....

1-1

.

Section

I

.

?

Page

11

INSTALLATlON

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

2-1

2.1

.

Introduction

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

2-1

2.3

.

Initial inspection

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

2-1

2.5

.

Power Requirements

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

2-1

2.7

.

Grounding Requirements

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

2-1

2.10

.

lnstallatiori

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

2-1

2.13

.

Repackaging

for

Shipment

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

2-1

i

1

Section Page

I11

OPERATING INSTRUCTIONS

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

3-1

3.1

.

Introduction

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

3-1

3.3

.

Low-Level Electrical Phenomena

.........

3-1

3.7

.

Turn& Procedure

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

3-1

3-8

.

Voltage Measurement

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

3-1

3.9

.

Current Measurement

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

3-1

0

.

Resistance Measurement

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

3-2

3-12

.

Amplifier Operation

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

3-3

Y

Section Page

Table

of

Contents

List

of

Tables

Section page

5.1

.

lntroduction

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

5-1

5.3

.

Required Test Equipment

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

5-1

5.5

.

Performance Checks

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

5-1

5.7

.

Meter Zero

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

5-1

5.10

.

Voltmeter Accuracy Check

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

5-1

1

.

Milliammeter Accuracy Clieck

..........

5-1

2

.

Ohmmeter Accuracy Check

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

5-2

5.13

.

Input KcsistanceClieck

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

5-3

5.14

.

AC Kejection Check

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

53

5.15

.

Adjustment and Calibration Proccdure

......

53

5.17

.

Cabinet Removal

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

53

5.18 .

Mechanical Adjustment of Meter Zero

....

5-3

5.20

.

Hum Balance Adjustment

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

5-5

5.21

.

Cathode

Follower

Bias Adjustrncnt

......

5-5

5.22

.

Meter Electrical Zero Adjustment

........

5-5

5.23

.

5.24

.

V

MAINTENANCE

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

5-1

Amplifier Gain Adjustment and

Meter Calibration

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

5-5

Olimmeter Adjustment

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

5-5

5.25

.

Troubleshooting

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

54

5.27

.

Front Panel Indications

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

54

5.29

.

Power Supply andAmplifier Checks

......

56

5.33

.

Modulator Clieck

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

54

5.34

.

Modulator Replacement

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

5-7

5.36

.

Demodulator Check

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

5-7

5.37

.

Demodulator Replacement

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

54

5.39

.

Switch Checks

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

5-8

541

.

Adjustment

of

Factory Selcctcd

Components

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

54

546

.

Input Cable Keplacemcnt

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

5-0

Section Pap

VI

REPLACEABLEPARTS

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

6-1

IV

THEORY

OF

OPERATION

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

4-1

6.1

.

lntroduction

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

6-1

4.1 .

General

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

4-1

64

.

Ordering Information

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

6-1

4.3

.

Block Diagram Analysis

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

4-1

6.6.

Non-Listed Parts

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

6-1

Section l’ilgc

4.9

.

Modulator. Amplifier. Demodulator.

VI1

CIRCUITDIAGRAMS

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

7-1

...........

4.5.

Range and Function Selection 4-1

4.7

.

Filters

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

4-1

and Chopper

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

4-1

7.1

.

Introduction

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

7-1

4-1

1

.

Cathode Follower and Polarity Selection

...

4-1

LIST

OF

TABLES

Page Number

Pagc

Number

1.1

.

Specifications

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

1.0

3.1

.

Voltage and Current in Resistance

Measurements

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

3-2

5.1

.

Test Equipment Required

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

54

5.2

.

Millianimeter Accuracy Check

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

5-2

5.3

.

Input Resistance Chccks

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

5-3

5.5

.

Tubc Replacement

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

541

6-1

.

Rcplaccablc Parts

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

6-2

54

.

Power Supply Voltages

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

:54

~

..

iii

List

of

Illustrations

n

Number

1-1.

Model

412A

DC

Vacuum Tube

Voltmeter

.

..

.

..

.

..

.

4-1.

Block Diagram

..

.

..

...

.

5-1.

Input Resistance Check

.

..

.

...

.

5-2.

AC

RejectionCheck

.

....

.

53.

Location

of

Adjustments

.

..

.

54.

Input Circuit Board

.

......

.

5-5.

ModulatorWaveform

...

.

...

.

54.

DemodulatorAssembly

....

5-7.

input Cable Connections.

.

...

.

5-8.

Simplified Schematic,Voltmeter

Switching

....

.

..

.

..

5-9.

Simplified Schematic,Ammeter

Switching

..

*

.

..

.

,

..

.

.1

t,p’

8

LIST

...........

.....e.....

’

OF

ILLUSTRATIONS

Page Number

,

.

,

1-1

,

.

,

4-1

.

5-2

..

.

53

...

54

...

56

.

..

5-7

...

s-8

...

59

.

.5-10

.

.5-11

5-1O.Simplified Schematic,Ohmmeter

Switching

.

...

.

...

.

..

...

.

....

6-1.

Location

of

Mechanical Parts,

Cabinet Model

.

...

.

..

.

6-2.

Location

of

Mechanical Parts,

Rack Model

.

...

.

....

.

6-3.

Voltage

Probe

Assembly

.

..

.

7-1.

Location of Chassis Mounted.Parts,

Cabinet Model

....

.

...

.

..

7-2.

Location

of

Chassis Mounted

Parts,

Rack Model

.

..

.

...

7-3.

Location

of

Switch

Components

.

..

74.

SchematicDiagram

.

..

.

7-5

Power

Supply Backdating

.

....

.

..

Model

4

12A

..........

e.........

..........

Page

.

.5-I

2

..

6-5

.

6.6

..6-7

.

7-2

..

7-3

..

74

.

7-5

.

7-7

b

'5

Section

I

Model

4

12A

Table

1-1.

Specifications

VOLTMETER

Voltage Range: Positive and negative voltages from

1

millivolt

fuull

scale to

1000

volts full scale in

13

9

ranges

Accuracy

:

+

1

%

of full scale onany range

Input Resistance:

10

megohms

1%

on

1

mV,

3

mV,

b

and

10

mV ranges

30

megohms

21%

on

30

mVrange

100

megohmsf.l%

on

100

mV range

200

megohms

t

1

%

on

300

mV range and above

AC Rejection: A voltage atpower line

or

twice power

line frequency

40

dB

greater

than full scale affects

reading

less

than

1%.

Peak voltage must not exceed

1500

volts.

AMMETER

Current Range: Positive and negative currentsfrom

1

microampere full scale to 1 ampere full scale in

thirteen ranges

Accuracy

:

2

2%offull scale on any range

v

tnput Resistance

:

tnternal Shunt Full

Scale

Range Resistance* Voltage

Drop

.001

mA

.003

mA

.01

mA

.03

mA

.I

mA

.3

mA

1

mA

3

mA

10

mA

30

mA

100

mA

300

mA

1000

mA

d

I000

ohms

3

I6

ohms

100

ohms

3

I

.6

ohms

IO

ohms

3.16

ohms

1

ohm

.3

16

ohm

.1

ohm

.I

olim

.I

olim

.I

ohin

.I

ohm

1

mV

0.9486

mV

1

mV

0.9486

mV

1mV

0.9486

mV

1

mV

0.9486

mV

1

mV

3

mV

10

mV

30

mV

100

mV

*For

total insertion resistance add

0.07

ohms copper lead

rcsistance at

25

C

OHMMETER

Hesistaticc Ibiige: Rcsistancc from

I

olim

center-scale to

IO0

niegolims center-scale in nine

decade

raiiges

a

Accuracy:

f-

5%

of

reading froni

0.3

to

3

on Ohms

scale

'I

14

Voltages and Currents:

Open Circuit ShortCircuit

Current

Range

Volts

XI

10

mV

10

mA

XI0

100

mV

10

mA

XI00

IV

10

mA

XlOOo

1v 1

mA

XlOK

1v

100~

A

XlOOK

1v

lop

A

XIM

XlOM

1v

.lp

A

Xl00M

1v

.Olp

A

1v

'P

A

AMPLIFIER

Voltage Cain:

1000

maximum

AC

Rejection:

3

dB at

1

Hz,

80

dBat

50

and

60

Hz

Output: Proportional

to

meter indication;

1

volt at

full scale; maximum current,

1

mA.

(Full

scale

corresponds to

1

.O

on upper scale.)

Output Impedance:

Less

than

2

ohmsatdc

Noise:

Less

than

5

mV

RMS

on

any range

Drift: negligible

GENERAL

Isolation Resistance: At least

100

megohms shunted

by 0.1~

F

between common terminal and case

(power line) ground

Common Mode Rejection: May be operated up to

500

Vdc

or

130

Vac from ground

Power: 115/230V

f10%,

5040

Hz,

35

W

Dimensions: Cabinet Mount:

11-1/2

in. high,

7-1/2

in. wide,

10

in. deep

Rack Mount:

001

29-5

Model

412A

1-1.

INTRODUCTION.

Section

I

SECTION

I

GENERAL

INFORMATION

1-2.

The Hewlett-Packard Model

412A/AR

DC

Vacuum

Tube Voltmeter is

a

multifunction instrument which

measures the entire range

of

dc voltages, current, and

resistance normally encountered in electronic equipment.

1-3.

The Model

412AIAR

measures dc voltage from

1.0

mV full scale to

IO00

V full scale in thirteen ranges

arranged in a

1,3,

10

sequence. Voltmeter accuracy is

1%

of

full scale. The input circuit

is

isolated from the case and

from

power line ground.

14.

The Model

412AlAR

measures positive

or

negativedc

current from

1.OpA

full scale

to

1.0

A

full scale with an

accuracy

of

2%

of

full scale. Current ranges are also in a

1,

3,

10

sequence.

1-5.

Resistance measurement capability

of

the Model

412AIAR

is

from

1.0

ohm center scale

to

I00

megohms

center scale in nine decade rangcs. Resistaiiccnieasureiiieiit

accuracy

is

5%

between

.3

and

3

on

the resistance scale.

16.

The Model

412AIAR

has

a

dc aiiiylifier output

voltage proportional to the input. Ainplificr giiiil is froiii

-1000

to

t1000,

depending on range selected.

1-7.

SPEC1

FlCATlONS.

1-8.

Complete specifications

for

the dip- Modcl41

2AIAR

are listed in Table

1-1.

1-9.

INSTRUMENT AND MANUAL IDENTIFICATION.

1-10.

Hewlett-Packard uses

a

twoscctioii cigltbdigit scrial

number

(OOO-00000).

If

the first tlircc digits

of

tlic

scrial

number

of

your instrumcnt do not agrcc witti thosc

on

tlic

title page of this manual, changc sliects supplicd

with

tlic

manual

will

explain the diffcrenccs bctwccii

your

instrument and the Model

412AIAll

dcscribcd

in

lliis

manual.

'

412A-A-30188

Figure

1.1.

Model

412A

DC

Vacuum Tube Voltmctcr

00

1

295

0

h

cy

P

Y

4b

4

J

Model

4

12A

2-1.

INTRODUCTION.

SECTION

II

IN

STACLATIO

N

2-2. Tliis section contains instructions necessary for

installation

of

the Model 412AIAR

DC

Vacuum Tube

Voltmeter. Included are initial inspection procedures,

power and grounding requirements, installation

information, and instructions for repackaging for shipment.

2-3.

INITIAL INSPECTION.

2-4.

This

instrument was carefully inspected both

mechanically

and

electrically before shipment. It should be

free

of

mars or scratches, and in perfect electrical order

upon receipt.

To

confirm this, the instrument should be

inspected for physical damage

in

transit.

Also

test the

clcctrical

performance

of

tlic instrument, using the

procedure outlined in Paragraph

5-5.

If

there is damage or

deficiency, see tlic warranty on the inside front cover of

this manual.

2.5.

POWER

REQUIREMENTS.

2-6.

The Model 412AIAR can be operated from any

source

of

115

or

230

volts at

50

or

60

Hz.

The

115/230

V

slide switch

on

the rear panel selects the desired voltage.

Power dissipationis approximately

35

watts.

2-7.

G

R

0

U

N

D

I

NG

REQUl

R

EMENTS.

2-8.

To protect operating personnel, the National

Electrical Manufacturer’s Association

(NEMA)

recommends

that tltc instrument panel and cabinet

be

grounded. This

instrument is equipped with a threeconductor power cable

wluch, when plugged into an appropriate receptacle.

grounds the instrument. The offset pin

on

the connector is

tlie ground wire.

2-9.

To

preserve the protection feature when operating the

instrument from a twocontact outlet, use a threeprong

to

two-prong adapter and connect the green pigtail

on

the

adapter toground.

NOTE

Operating the Model 412A/AR without

grounding the third (power line ground)

wire

of

the power cable will result

in

a

zero offset

of

the meter and oscillation

of

the pointer.

2-1

0.

INSTA

1

LATlON.

Section

I1

2-1

I.

The Model 412A is intended

for

use

as

a

bcncli

instrument, having a top-mounted handle and rubbcr fcct.

2-12. The Model 412AR is intended for rack mounting.

Front panel height

is

5-7/32 inches.

2-13.

REPACKAGING

FOR

SHIPMENT.

2-14.

The following paragraphs contain

a

general guidc for

repackaging

of

tlie instrument. Rcfcr to Paragraph

2-15

if

the original container is

to

be

uscd;

2-16

if

it

is

not.

If

you

have any questions, contact your

local

-lip-

Salcs

and

Service Office. (SCCAppendix

B

for office locatiwis.)

NOTE

If

the instrumcnt is to be sliippcd

to

I

Icwlctt-i’ackard for scrvicc

or

repair.

attach a tag to tlic instrumcnt idcntifying

the owncr and indicating tlic scrvicc

or

repair

to

be accomplislicd. lncludc tlic

model number

of

tltc instrumcnt.

In

any

corrcspondcnce, identify tlic instrumcnt

by modcl numbcr, scrial numbcr prcfix,

and scrial numbcr.

2-15. Place the instrumcnt

in

original conhincr with

suitable packing material and

scat

wcll

with strong tapc

or

metal bands.

If

original containcr

is

not aviilablc, onc

CBR

be

purchased from your ncarcst

hp

Salcs

and

Scrvicc

Office.

2-16.lf original container

is

not to hc uscd, procccd

as

follows:

a. Wrap instrument

in

hcavy

papcr or plastic hcfurc

placing in an inncr containcr.

b.

Place packing material around a11

sidcs

of

instrumcnt and protcct panel facc

with

cardhturd

strips

.

c. Place instrument and inncr containcr

in

a hcavy

carton

or

wooden box and scal wcll with strong

tapc

or

metal hands.

d. Mark shipping containcr

“DI~LICATE

INSTIWMENT,”

“FRAGILE,” ctc.

00

1

29-5

2-1

hlodcl4

12A

SECTION

111

0

PER

AT1

N

G

3-1.

INTRODUCTION.

3-2.

The

-lip-

Model 412A/AR

DC

Vacuum Tube

Voltmeter nieasures dc voltages from

1.0

mV full scale to

lo00 V

full

scale with

an

accuracy of

1%

of

full

scale.

Current measurement ranges are from

0.001

mA

full

scale

to

1000

mA

full

scale, with accuracy

of

2%

of

full scale.

The Model

41

2A/AR makcs resistaricc measurements from

1.0

ohm center

scale

to

100

megohms center scale.

Resistance measurenicnt accuracy is

5%

of

reading between

.3

and

3

on

the ohms scale.

A

dc amplifier output is also

provided.

Voltage

gain of tlic amplificr is from

-1000

to

+1000,

depending

on

range selcctcd. Amplifier output is

1

.O

V

at full scale. and maxinium current load is

1

.O

mA.

3-3.

LOW-LEVEL ELECTRICAL PHENOMENA.

34.

Stray low-level electrical phenomena may cause error

in

low voltage measurements. When using the lower voltages

of the Model 412A, consider the possibility

of

low-level

voltages produced by thermoelectric effects, residual

charges on capacitors, battery action,

or

flexing

of

coaxial

cables,

3-5.

The voltagc probe, currentlresistance lead, and

common lead

of

the Model 412A/AR are all designed to

have a very low thermoelectric effect with copper, the most

commonly used conductor. However, some component

leads such as transistors and reed relays may have leads

made

of

such alloys as nickel-iron, which produce a

thermoelectric voltage when joined with copper. Whenever

possiblc, connect tlic

412A

leads to copper. If this

is

not

possible, the voltage probe and common lead should both

In:

conncctcd

to

the

smic

kind

of

inctal compncnt lead,

and both connection points maintained at the same

tc

111

pcra

t

urc.

34.

To minimize tlic possibility

of

battery action when

making

low

voltage mcasurcments, make sure the 412A

probe tip and common lcad alligatorclip are clean.

Also

be

surc

tlic component leads or other points of connection are

clean. The prcsence

of

sonic chemicals such

as

solder flux

niay cause noticeable nieasiirement error due to battery

action.

NOTE

Operating the Model 412A/AR without

grounding the third (power line ground)

wire

of

the power cable will result in a

zero offset

of

the meter and oscillation

of

the pointer.

IN

STRU

CTiO

NS

3-7.

TURN-ON PROCEDURE.

Section

111

BEFORE CONNECTING PRIMARY

POWER, MAKE SURE THE REAR

PANEL 115/230 V SLIDE SWITCH

IS

SET

TO

THE POWER LlNE

VOLTAGE

TO

BE

USED.

INCORRECT SETTING MAY

RESULT IN DAMAGE TO THE

INSTRUMENT.

a. Make sure the proper fuse is installed for operation

with the power line voltage to be used. A

0.6

A

slow-blow fuse should be used for

I

IS

V

operation, and a

0.4

A slow-blow fuse for

230

V

operation.

b. Connect

to

ac power and turn instrument ON.

Allow

a

S-minute warm-up period.

3-8.

VOLTAGE

MEASUREMENT.

a.

Set

FUNCTION switch to VOLTS, and select

proper polarity.

b. Set RANGE switch to desired range.

If

in doubt,

set

switch to high range and downrange as

necessary.

c.

Connect VOLTS and

COM

leads across circuit

or

component, and read voltage.

DO

NOT OVEKLOAD THE

INSTRUMENT. MOMENTARY

OVERLOADS UP TO TEN TIMES

FULL SCALE WILL NOT DAMAGE

THE INSTRUMENT; HOWEVER,

CURRENT SHUNTS, AND

INTERNAL RESISTANCE

STANDARDS ARE NOT

PROTECTED FROM EXTREME

OVERLOAD.

33.

CURRENT MEASUREMENT.

a. Set FUNCTION switch to

MA.

b.

Set RANGE switch to desired range.

If

in doubt,

select high range and downrangeas necessary.

00

1

29-5

3-1

section

111

Resistance Range

.

c. Deenergizecircuit

to

be

measured.

OpenCircuit Volts

(at

1

on top scale)

d. Connect

412A

into circuit,

using

MA/OHMS

and

COM leads.

e.

Energize circuit,

set

POLARITY

switch

for

up-scale indication, and read current.

NOTE

When making current measurements,

make

sure

there

is

noconnection between

the circuit common

6)

and power line

ground (&)terminals on rear panel.

3-10.

RESISTANCE

MEASUREMENT.

a.

Set

FUNCTIONswitch

to

OHMS.

b.

If resistance

to

be

measured

is

part of a circuit,

make sure

power

is

turned

off.

c.

Connect

412A

across circuit

or

component

to

be

measured,using

MA/OHMS

and COM leads.

XI

XI0

XI00

X1

K

XlOK

XlOOK

XIM

XlOM

XlOOM

Model

41

2A

d.

Set

RANGE switch

so

that meter indication is as

near center scale as possible, and read resistance on

OHMS

scale.

3-1

1.

When measuring the resistance

of

non-linear devices

such as transistors and diodes, it is often desirable

to

know

what voltage and current were present in obtaining the

resistance measurement. Table

3-1

lists the open-circuit

voltage and shortcircuit current availableat

the

412A

leads

during resistance measurements. Voltage and current are

read on the top scale

of

the meter

for

all

resistance ranges.

The meter reading is directly proportional

to

the voltage

across the device being measured, and inversely

proportional

to

the current.

As

an example, assume that

a

device being measured on the

XI0

range gives a reading

of

.25

on

the resistance scale. The meter

also

indicates

.2

on

the

top

scale. Since full-scale voltage for the

XI0

range is

100

mV (Table

34),

this indicates a voltage

of

20

mV

across the device. To determine the current, subtract the

meter reading

of

.2

from the full scale reading

of

1,

and

multiply by the shortcircuit current listed in Table

3-1

.

Since the current shown

for

the

XI0

range

is

10

mA,

this

indicates

a

current

of

8

mA through the device being

measured. The resistance measurement, then, indicates an

equivalent resistance

of

2.5

ohms, with an applied voltage

of

20

mV, and a current

of

8

mA.

Table

3-1.

Voltage and Current in Resistance Measurements

1

10

mV

100

mV

IV

1v

IV

1v

ShortCircuitCurrent

(at

0

on tot, scale)

10

mA

10

mA

10

mA

1

mA

l00pA

IO

pA

lPA

0.1

pA

0.01

pA

3-2

00

1

29-5

Model

4

12A

Section

111

3-12.

AMPLIFIER OPERATION.

at full scale; maximum rated load current is

1

.O

mA.

Load

currents

in

excess

of

1.0

mA (less than

1000

ohms load

3-13.

The Model

412A/AR

DC

Amplifier Output may be resistance) may cause errors in meter indication and

used todrive devices

such

as an analog recorder toprovide a amplifier

gain.

Amplifier gain is from

+lo00

on the

,001

permanent record

of

measurements. Output level is

1

.O

volt range

to

-1000

on the

loo0

range.

4

Y

00

1

29-5

I‘

3-3

Model

412A

SECTION

IV

THEORY

OF

OPERATION

4-1.

GENERAL.

4-2.

The kp- Model

412AIAR

uses a chopper-stabilized

amplifier circuit to produce a meter indication proportional

to the voltage,current, or resistance being measured.

4-3.

BLOCK

DIAGRAMANALYSIS.

44.

Figure

4-1

is

a block diagram

of

the Model

412AIAR.

The following paragraphs describe operation of the various

circuits.

4.5.

RANGE AND FUNCTION SELECTION.

4-6.

The Voltage Divider. Current Shunts, and Resistance

Standards circuits provide a

0.9

mV output for full-scale

input in all ranges and functions. Full scale

is

defined as a

reading

of

1

on

the top scale of the meter for all ranges.

Simplified schematics

of

the switchingcircuits

for

all ranges

and

functionsare shown in Figures

5-8

through

5-10,

47.

FILTERS.

4-8.

input filtering is provided to attenuate any ac

components present in the input signal. The second fdter

section filters the Demodulator output.

RANOC

SELtCllOW

r

Section

1V

4-9.

MODULATOR, AMPLIFIER, DEMODULATOR,

AN0

CHOPPER.

4-10. A

light-beam chopper driven by a synchronous motor

sets the Modulator/Demodulator frequency at

516

power

line frequency. The Modulator output is an ac signal

proportional

to

the Model

412A

input. The amplifier

gain

is

stabilized at

1

,111

by the feedback network, resultingin an

output

of

1

.O

volt for a full-scaleinput. The Demodulator

is

synchronized with the Modulator

so

that the amplified ac

signal

is

converted to

a

steady dc, which

is

applied

to

the

Cathode Follower. This voltage is the same polarity as the

input signal.

4-11.

CATHODE FOLLOWER AND POLARITY

SELECTION.

4-12.The Cathode Follower drives the Meter and the

DC

Amplifier Output. Polarity selection provides upscale

meter reading for either polarity input. The Polarity switch

is disabled in the

OHMS

function.

I

Figure

4-1.

Block Diagram

00

129-5 4-1

6

Section V Model 412A

INSTRUMENT

TYPE

DC

Voltage Standard

Variable Line Transformer

DC

Voltmeter

AC

Voltmeter

~ ~ ~~

Oscilloscope

Precision Resistors

Oscillator

Table

5-1.

Test Equipment Required

REQUIRED CHARACTERISTICS

Range:

0-300V

Accuracy:

0.1%

Current Rating:

10

mA

Output Voltage:

to

127

Vac

(or

253 Vac)

Range:

1

V

to

300

V

Resolution

:

10

mV

Input Resistance:

100

Ma

Range: to

300

V

Range: to

10

Ma

Sensitivity:

0.01

Vlcm

Resistance:

1

10

100

1K

10

K

30K

5W

100K

1W

300

K

1/2

W

1M

10

M

100

M

10

M

Accuracy

:

i

1.0%

2

1.0%

f

1.0%

f

1.0%

+,

1.0%

?

0.1%

2

0.1%

2

0.1%

2

0.1%

2

1.0%

2

1.0%

k

0.1%

-~

~

Frequency

:

60Hz

Output:

IO

V peak

hp-738BR Voltmeter

Calibrator

1

Superior Electric

Powerstat 3PF116

(for

1

15

V line) 3PF216

(for 230

V

line)

hp-427A Voltmeter

hp-

427A Voltmeter

hp-427A Voltmeter

hp

120B

Oscilloscope

Part Number:

-hP-

08

1

I-OoFiO

-hP-

hP-

07574346

0757.040

1

-hp-

07574280

-hP- 07574442

Daven

DAS-5

Dale

MF-I

Dale MFS-112

-hP

0698416

1

0733401

7

-hP

0698-5049

-hP-

08

1

1-2475

-hp-

200CD Wide Range

Oscillator

Model

4

12A

SECTION

V

MAINTENANCE

5-1.

INTRODUCTION.

5-2.

This section contains information necessary to

maintain the kp- Model 412A/AR. The following

paragraphs describe the Performance Checks, Calibration

Procedures, Troubleshooting, and ServicingProcedures.

5-3.

REQUIRED TEST EQUIPMENT.

54.

Recommended test equipment for maintaining and

checking performance

of

the Model 412A is listed in Table

5-1.

Test

instruments other than those recommended may

be

used if their specifications equal

or

exceed the required

characteristics.

55.

PERFORMANCE CHECKS.

5-6.

Use

the following procedures to verify proper

operation of the Model 412A. The 412A and test

equipment should

be

operated at 115/230 Vac unless

otherwise specified. A Performance Test Card is provided at

the end of this section for recording the performance of the

Model 412A. The card may

be

removed from the manual

and used as a permanent record

of

the incominginspection

or

of

a routine performance check. If the Model 412A does

not meet specificationsat

any

point in this procedure, refer

to Paragraph

5-1

5,

Adjustment and Calibration procedure.

5-7.

METER

ZERO.

5-8.

The meter pointer should rest over the zero

calibration mark when the instrument is at normal

operating temperature, is turned off, and is in the normal

operating position.

If

the pointer is off

zero,

perform the

mechanical adjustment procedure outlined in Paragraph

5-1

8

before proceeding with the performance checks.

5-9.

Turn the Model 412A POWER switch ON. After a

5-minute warm-up period, the meter pointer should rest on

zero

when the input leads are shorted. If not, perform the

electrical zero adjustment outlined in Paragraph 5-22.

Section

V

5-10.

VOLTMETER ACCURACY CHECK.

a.

A

dc voltage standard and a variable line

transformer are required

for

this chcck.

If

an -tip-

Model 738BR Voltmeter Calibrator is used, it

should be alloweda 30-minute warm-up period.

b. Connect 412A

to

variable line transformer, and set

line voltage switch (1

15/230)

tocorrespond toline

voltage being used. Turn 412A ON and allow

5-minute warm-up period.

c.

Set 412A FUNCTION to VOLTS, POLARITY to

+.

d. Connect VOLTS and COM leads to dc standard

output.

e.

Check 412A indication againstdcstandard output

at full scale

on

each 412A range. Maximum error

should be

no

greater than

f

1%

of full scale (one

small division

on

topscale).

NOTE

When checking the Modcl 412A

on

the .001 and

.003

volt ranges, turn

off the dc standard output and note

any 412A

zero

offset due

to

thermoelectric voltage. Add

or

subtract

as

necessary any offset from

the 412A reading.

f. Check 412A meter tracking

on

the

1

V rangat

all

cardinal points on the meter scale. Maximum crror

should be no greater than

0.01

V

with cithcr

polarity input.

.

g. Repeat step e on

1

V

range at line voltagesof

103

and I27volts

(or

207and 253 V).

NOTE

5-11.

MILLIAMMETER ACCURACY CHECK.

Operating the Model 412A/AR without

grounding the third (power line ground)

wire of the power cable will result in a

zero offset of the meter and oscillation

of

the printer.

a. A dc voltage standard and the prccision rcsistors

listed in Table

5-2

rcquircd

for

this chcck.

b. Set 412A FUNCTION toMA. I’OLARITY to

+.

001

29-5

5-1

Section

V

DC

Standard

output

IV

3v

.O

1

10

v

.03

30

V

.I

100

v

.3

300

v

1

300

V

3

300

V

IO

300

V

30

300

V

3

Range Series

Resistance

I.00M

t

0.1%

1

.OOM

t

0.1%

1.00M~O.I%

1

.OOM

2

0.1%

I

.OOM

2

0.1%

1.00M?

0.1%

300K

iO.l%

1/2

W

lOOK

20.1%

1

W

30K

2

0.1%

5

W

30K

to.]%

5

W

Model

4

12A

Table

5-2.

Milliammeter Accuracy Check

Model

4

1

2A Reading

(

2%

of full scale)

1

.o

3

.O

1

.o

3

.O

1

.o

3

.O

1

-0

3

.O

1

.o

1

.O

(on

3

scale)

c.

Connect Precision Resistor in series with MA lead

and positive side

of

dc standard output. Connect

412A

COM lead to dc standard negative output

terminal.

Paragraph

5-10.

changes. Figure

5-9

shows simplified ammeter switching

circuits.

5-12.

OHMMETER

ACCURACY

CHECK.

d. Perform checkslisted in Table

5-2.

a.

Set

FUNCTION

selector

to

OHMS.

NOTE

It is not necessary

to

check higher current

ranges.

On

current ranges

10

through

1000, the current shunt does not change.

Only the voltage divider, checked in

b. Connect, in turn, resistor

of

1,10,100,1

K,

10

K,

100

K,

1

M,

10

M,

and

100

M

ohms+I.O%

between MA/OHMS and COM leads. With

appropriate RANGE setting, meter should indicate

between

0.95

and

1.05

in each case.

-hp-

MODEL

412A

DC

STANDARD

-hp-

MODEL

738BR

I

~

Figure

5-1.

Input Resistance Check

5-2

001

29-5

J

i

h

9

c

D

J

b

1

412A

Input

'

Resistance

Model 4

12A

5-13.

INPUT RESISTANCE

CHECK.

a.

Connect the Model 412A/AR, dc standard and

10

rnegolim resistor

as

shown

in

.Figure

5-1.

b.

Set 412A

FUNCTION

to

VOLTS,

POLARITY to

+.

c. Adjust

412A

RANGE and dc standard output to

voltages listed in Table

5-3.

A

correct meter

reading in each case verifies the input resistance

where:

Ein

=

Eapplied

[

&&]

Table

5-3.

Input Resistance Checks

100

mV

412A

Meter

Reading

(?

1

%)

5.0

mV

22.5

mV

90.9

mV

0.95

V

IOMQ

30

Ma

100

Ma

200

Ma

Section

V

c. Set ac voltmeter FUNCTION

to

AC

VOLTS,

RANGE to

IO

V.

d. Adjust oscillator frequency to

60

Hz,

and adjust

output for an indication

of

7.07

V

on

ac

voltmeter. This corresponds

to

a

IO

V

pcak

;IC

noise signal at the

412A

input.

e. The 412A meter rcadingshould

be

02

I%(l

minor

division

on

upper scale)..

5-15.

ADJUSTMENT AND CALIBRATION

PROCEDURE.

5-16.

The followingproccdures should bc pcrfornicd

only

if

it has been determined by the Performance Chccksoutlincd

in

Paragraph

5-5

that the Model

412A/AR

docs

not

iiicct

specifications.

5-17.

CABINET REMOVAL.

a. Disconnect power cord from powcr source.

b.

On cabinet model, rcmovc two rctaining

scrcws

near center of rear panel. On rack modcl, rciiiovc

three retaining screws

in

rcar

of

covcr.

c.

Slideinstrument chassis forward

out

of

cabinct.

5-18.

MECHANICAL ADJUSTMENT

OF

METER

ZERO.

5-14.

AC

REJECTION

CHECK.

5-19.

If

mechanical zero

of

mctcr is corrcct, pointcr rcsts

over the zero calibration mark

on

thc nwtcr scalc wlicii

voltmeter as shown in Figure

5-2.

instrument is at normal opcrating tcmpcraturc,

in

its

normal operating position, and turncd

off.

If

nicclianical

zero is not corrcct, perform thc following adjuslment

procedure.

a.

Connect the Model

412A/AK,

oscillator, and ac

b.

Set 412A FUNCTION to

VOLTS,

POLARITY to

+,

and RANGE to

0.1

V.

-hp-

MODEL

412A

OSCILLATOR

hp

200CD

Figure

5-2.

AC

Rejection Check

001

29-5

5

-3

J

Section

V

19

Model

4

I

2A

*7

3.

C

R46

-

METER

CAL

-

4

10,

CAL

-

R126

HUM

BAL

n

GAIN

CAL

R126

HUM

BAL

Figure

5-3.

Location

of

Adjustments

00

I

29-5

Model

4

12A

a. Turn 412A ON and allow a 20-minute warm-up

period. This

allows

meter movement

to

reach

normal operating tcniperaturc.

b. Turn instrumcnt OFF and allow

30

seconds for all

capacitors

to

discharge.

c.

Rotate mechanical zero-adjustment screw

clockwise until meter pointer is toleft of zero and

moving upscale toward zero.

d. Continue to rotate adjustment screw clockwise

and stop when pointer

is

exactly over zero mark.

If pointer overshoots zero, repeat steps

c

and d.

e. With pointer exactly on zero, rotate adjustment

screw counterclockwise approximately

10

degrees.

This frees adjustment screw from meter

suspension. If pointer moves during this step,

repeat steps

c

through e.

5-20.

HUM BALANCE ADJUSTMENT.

a. Turn

412A

ON and allow 5-minute warm-up

period.

b.

SetFUNCTION

to

VOLTS.

c.

Connect oscilloscope to

DC

AMPLIFIER

OUTPUT.

d. Adjust HUM BAL (R126, Figure

5-3)

for

minimum

10

Hz

signal

on

oscilloscope. (If power

line frequency is

50

Hz, beat frequency will be

8-1/3

Hz instead of

10

Hz.)

NOTE

The Hum

Bal.

control docs not affect

the 120

Hz

ripple. Adjust only for

minimum 10

Iiz

(or

8-1/3

Hz) signal.

With the VOLTS lead shorted

to

COM

lead and POLARITY set

to

t,

the 412A meter will show a

minimum deflection when the Hum

Bal.

is

correctly adjusted.

5-21.

CATHODE FOLLOWER BIAS ADJUSTMENT.

a.

Set

412A

RANGE

switch fully clockwise (one step

beyond 1000).

b. Adjust rear panel BIAS

ADJ

(R116)

to

set

meter

pointer approximately on zero. This adjustment is

not critical, since

any

deviation from zero is

reduced more

than

100

times when the RANGE

switch is in any operating position.

00

129-5

Section

V

5-22.

METER ELECTRICAL ZERO ADJUSTMENT.

NOTE

Meter electrical zero adjust circuit

may not

be

installed in 412A cabinet

model instruments with serial

number 424-14482 and below, or

in

41

2AR rack mount instruments with

serial number 424-15082 and below.

a. Turn 412A ON and allow

a

30-minute warm-up

period.

b. Set FUNCTION

to

VOLTS, RANGE

to

.001.

c.

Short VOLTS probe

to

COM lead.

d. Adjust ZERO ADJ (R129) for zero dcflcction of

the meter pointer. Check the zcro adjustmcnt by

switching POLARITY from

t

to

-

When zero

is

adjusted properly, this action should produce a

minimum amount of deflection.

5-23.

AMPLIFIER

GAIN

ADJUSTMENT AND METER

CALI

B

R

AT1

0

N

.

a.

A

dc standard and

a

de voltmeter arc rcquircd for

these adjustments.

b.

Connect

4

12A VOLTS probe and COM lcad

to

dc

standard output.

Set

FUNCTION

to

VOLTS,

RANGE

to

1

V,

POLARITY to

t.

c.

Connect dcvoltmeter betwccn dc standard output

(t)

and412A

DC

AMPLIFIER OUTPUT liigli.

d.

Set

dcstandard output to

+I

V.

e.

Adjust 412A GAIN

CAL

(RI

19)

for zcro

indication on test voltmctcr.

A

10

mV rcading

on

test voltmcter indicates

1%

crror in

4

12A gain

calibration.

f. Adjust METER CAL (R46) to sct 412A meter

pointer on

1.0

on top scale. Disconnect test

voltmctcr.

g.

Chcck 4l2A calibration at full scalc on all ranges

as outlined

in

Paragraph

5-10.

If

any rcading

is

in

error morc than

I%,

rcadjusl

GAIN

CAL

(It1

19)

to

bring

all

readings within

f

1

X.

5-24.

OHMMETER ADJUSTMENT.

a. Set 412A FUNCTION toOIIMS, ItANGIi to

XI

K.

Make ccrtain

MA/OlIMS

and (:OM

lcads

are not

connected through wmccxtcrnal rcsistancc.

5-5

Section

V

Check Point

b. Adjust rear panel OHMS ADS (R36) for meter

indication

of

aD

(corresponding to

1.0

on upper

scale).

Voltage

525.

TROUBLESHOOTING.

5-26. When the Model 412A/AR operates improperly, first

adjust and calibrate it according

to

the procedures outlined

in Paragraph

5-15.

If

calibration

is

not possible, procecd

with the troubleshooting steps.

CONTAMINATION OR

FINGERPRINTS ON THE RANGE

SWITCH

OR

THE COMPONENTS

MOUNTED

ON

THE RANGE SWITCH

MAY REDUCE ACCURACY OF

INSTRUMENT.

5-27.

FRONT

PANEL INDICATIONS.

5-28.

If the malfunction is common

to

all

ranges and

functions, the trouble may be in the amplifier or power

supply areas. If the instrument operates improperly on only

one range

or

function, the trouble

is

probably in the

switchingsection

or

input cables.

5-29.

POWER SUPPLY

AND

AMPLIFIER CHECKS.

5-30.

Check power supply voltages at pointslisted in Table

5-4.

Voltages are measured with respect

to

circuit common

(A).

Figure

7-2

shows the location

of

components.

53

1.

Tubes are

a

coinmon source

of

trouble and are most

easily checked by substitution. Following replacement

of

a

particular tube, iiiake the adjustrneiits indicated

in

Table

5-5.

5-32.

Additional

checks

of

amplifier operation niay be

made

by

cliecking

voltages shown

on

the amplifier section

of

tlic

sclrwutic diagram.

Be

sure

to

observe conditions

in

Note

I1

in

Paragraph

7-2.

Allow

3

tolerance

of

210%.

5-6

Model

4

12A

Table

5-5.

Tube Iteplacement

Tube Iteplaced

VI01 (12AX7) Amplifier

V102 (6AU8) Amplifier/

Cathode Follower

V103 (6x4) Rectifier

V104 (OA2) Regulator

VI05 (OB2) Regulator

5-33.

MODULATOR

CHECK.

Adjustment

Huni

Bal.

Par.

5-20

Gain Cal. Par.

5-23

Bias

Adj.

Par.

5-21

Cain

Cal.

Par.

5-23

None

Ohms Adj.

Par.

5-24

-71

a.

An oscilloscope and

a

10

Maresistor are required

for this test.

b.

Disconnect 412A from power source and remove

cabinet.

c.

Remove VlOl and reconnect 412A to power

source.

d. Connect

a

clip lead

from

the center arm

of

R116

(rear panel

BIAS

ADJ) to the termination

of

the

VOLTS input cable (terminal

4

in Figure

5-7).

e. Set 412A FUNCTION to VOLTS, RANGE to

.001.

f.

Set oscilloscope input to

DC.

g.

Connect a

10

Mfi

resistor in series with

oscilloscope vertical input. Using a clip lead,

connect resistor

to

junction

of

RlOl and ClOl

(input circuit board, Figure 54). Connect

oscilloscope common to 412A COM lead. Set

Vertical Sensitivity

to

0.2

V/cm.

I

Figure

54.

Input

Circuit

Board

00

1

29-5

Model

4

12A

h. Turn 412A ON and allow 30-second warm-up

period. Observe de voltage amplitude on

oscilloscope.

i. Move oscilloscopc input (with series resistor) to

Modulator output at junction of green lead from

Modulator and C104

(0.01

Microfarads).

j.

Waveform should be similar

to

that shown in

Figure

5-5.

Peak-to-peak amplitude should be

approximately equal

to

dcvoltage observed in step

h. Signal frequency sliould be

5/6

power line

frequency.

k. If waveform is not satisfactory, check chopper

motor and assembly or Modulator and input

circuit as indicated by deficiency in waveform.

p-20

MSEC-

--)1

Figure

55.

Modulator Waveform

5-34.

MODULATOR

REPLACEMENT.

5-35.

The photoconductor cells in the Modulator

(VllOA/B) are not separately replaceable.

If

a

cell

is

defective, the Modulator block assembly should be

replaced, using the following procedure.

a. Disconnect 412A from power source and remove

cabinet.

CONTAMlNATION OR

FINGERPRINTS

ON

THE RANGE

SWITCH OR COMPONENTS

MOUNTED

ON

THE RANGE

SWlTCII MAY KEDUCE

ACCURACY

OF

THE

INSTRUMENT.

b.

In 412A cabinet model, remove side shield.

c.

Note and record color code of wires before

removing from Modulator assembly printed circuit

board.

001

29-5

Section

V

d. Remove four screws holding light-beam chopper

assembly. It is not necessary to disconnect wires.

e. Spread grip rings on Modulator light rods and slide

rods out

of

Modulator block.

f. Remove four screws holding modulator assembly

to

chassis.

NOTE

Be

sure

to

seat the four insulating

shoulder washers in mounting holcs

when replacing the assembly.

g.

Lift out Modulator assembly. If it is necessary to

replace Modulator block asscmbly only, rcmovc

four screws holding printed circuit board

to

block.

Note color and location

of

wircs between block

and printed circuit board before disconnccting.

5-36.

DEMODULATOR

CHECK.

a.

Disconnect 412A from powcr sourcc and removc

cabinet.

b. Remove V102 (on Amplifier Assembly).

c.

On

iight-beam chopper assembly, rcmove uppcr

lamp nearest front of instrument. This

lamp

illuminates

VI

1

I

A.

d. Connect a

1.0

microfarad capacitor across input

terminals of test ohmmeter.

e. Connect test ohmmeter common lead

to

Demodulator terminal with pinklorange wirc.

Sec

Figure

56.

f. Connect other

test

ohmmeter lcad to tcrminal

with whitelorange wire.

g.

Connect 412A

to

power source and turn

ON.

.

h. Resistance indicated on

test

ohmmeter

should

bc

I

to 2 megohms.

i. Turn

41

2A

OFF.

j.

Replace lamp in light-beam chopper and remove

upper lamp nearest rear of instrument. This lamp

illuminates

VI

I

1

B.

k. Connect test ohmmeter common lcad to

Demodulator terminal with brownlorange wirc.

5

-7

.

,

.

. -.

.

,

.

._...

.

..

-

..

.,

.

. --*w

”-

Section

V

b

I.

Connect other test ohmmeter lead to terminal

with whitelorange wire.

m.Turn412AON.

n. Resistance indicated on test ohmmetershould be

I

b

to2 megohms.

0.

Turn

41

2A OFFand replace lamp and

V102.

Iy

5-37. DEMODULATOR REPLACEMENT.

5-38.

The photoconductors in the Demodulator are not

separately replaceable. If a

cell

is defective, the

Demodulator assembly should

be

replaced, using the

following procedure:

a. Disconnect instrument from power source and

remove cabinet.

b.

Disconnect the three wires

to

Demodulator

assembly. Figure

5-6

shows wire

color

codes for

both cabinet (4 12A)and rack (4 12AR)models.

c. Remove four screws holding light-beam chopper.

It

is

not necessary todisconnect wires.

d.

Remove nuts from four screws holding

.I

Demodulator assembly and remove assembly from

instrument.

5-39.SWITCH CHECKS.

CLEAN RUBBER GLOVES SHOULD

BE WORN WHEN WORKING ON

THE

RANGE SWITCH. CONTAMINATION

6

5-8

412A

(CABINET

MODEL)

412A-8-50160

Model 412A

OR FINGERPRINTS MAY KEDUCE

ACCURACY OF INSTRUMENT. IN

ADDITION, LOW ROSIN CONTENT

SOLDER SHOULD BE USED WHEN

REPLACING COMPONENTS. USE A

MINIMUM OF HEAT WHEN

SOLDERING, AND REMOVE TRACES

OF

FLUX

FROM CONNECTIONS. IF

NECESSARY, RANGE SWITCH MAY

BE CLEANED USING A SOLUTIONOF

MILD DETERGENT AND WARM

WATER. RINSE THOROUGHLY IN

DISTILLED WATER AND

DRY

IMMEDIATELY.

540.If

the malfunction is peculiar to one range

or

function, trouble may be in the switching circuits. Either a

component

or

switch contact may be defective. Figures

58

through

5-10

show simplified schematics of range and

function switching, and may be used toisolate the trouble.

For example, if the instrument operates properly on all

voltage rangesexcept

.003;

R1, R9,

or

the associated switch

contacts may be defective. Figure

7-3

identifies the

componentsmountcd on the

rmgc

switch.

5-41.

ADJUSTMENT

OF

FACTORY

SELECTED

COMPONENTS.

542. R34*.

5-43.

The value of

R34*

is selected tobring the OHMS ADJ

potentiometer within the proper range, and is dependent

upon the power supply voltage and the value

of

other

resistors in the ohmmeter circuit. Replacement

of

R34*

should not be necessary unless V104 has been replaced

or

the range switch components have been changed.

If

the

VI

412AR

(RACK

MODEL)

Figure

56

Demodulator Assembly

TO

Cl13

TO

C114

AND

Rll7

TO

RI

16

00

1

29-5

HP 412A Service manual

Popular Measuring Instrument manuals by other brands