RCA WV-38A Operating And Maintenance Instructions Manual

SUGGESTED

PRICE

5Q CENTS

operating and
maintenance instructions

RCA

Volt-Ohm-Milliammeter

Safety Precautions

For

proper operation, the ground (black) lead of the

should

be connected to the ground of the equipment under
any other connections are made. An important point to remember is
that

there

Therefore,

equipment under

is always danger inherent in testing electrical equipment.
the operator should thoroughly

test

before

working

on it, bearing in

familiarize

himself

mind

voltages may appear at unexpected points in defective equipment.

tional

precautions

which

experience in the industry has shown to be

important are listed below:

WV-38A

test,

before

with

that

the

high

Addi-

1. It is good practice to remove power before connecting

test

leads
to high-voltage points. If this is impractical, be especially careful to
avoid

ing

leads. Check

accidental contact

can

provide a ground.

on a properly insulated

2.

Filter

Therefore,

3.

Remember

tional
with

hazard of high voltages appearing at exposed points along the

them.

4.

To lessen the danger of accidental shock, disconnect

immediately

5. Remember

sible

hazards.

capacitors may store a charge large enough to be lethal.

discharge

that

test

leads for frayed or broken insulation before

after

test

that

Even

with

Working

equipment racks and other objects

with

floor

filter

capacitors before attaching

leads

with

is completed.

the

risk

a minor shock can place the operator in jeopardy of

more serious risks, such as a bad

one hand in your pocket and stand-

lessens the danger of shock.

test

leads.

broken insulation provide the addi-

working

test

of severe shock is

fall

or contact

only

with

one of the pos-

a source of higher

which

leads

voltage.

6. The experienced operator continuously guards against injury

and does not work on hazardous circuits unless another person is

avail-

able to assist in case of accident.

Trade

Mark(s)

Marca(s) Registrada(s)

® Registered

3/71

RCA

Volt-Ohm-Milliammeter

Description

The

RCA
all-purpose measuring instrument. The
AC

sine-wave voltages

volt

to 5000 volts; DC current

from

0.2 ohm to 20 megohms; and decibels

resistance is 20,000 ohms-per-volt on DC, and 5000 ohms-per-volt on AC.

Features of this versatile
resistors in all measuring circuits, and a large, easy-to-read meter
sensitive
two-color

positions.

of

the

50/zA

markings for

A

convenient function switch is provided

The +DC and

test
resistance ratio of electrolytic capacitors and many types of semi-conductor
devices.

Two

special
against burnout due to accidental overload.* A fuse protects the precision
multiplier

source.

in the ohms network.

The

WV-38A

Five
(4 penlight cells and 1
pounds, and measures 6% inches by 5^4 inches by
clips

are provided on the handle for carrying the

is

attractively styled,

WV-38A

Volt-Ohm-Milliammeter

WV-38A

from

0.1
from

volt

to 5000 volts; DC voltages

1 microampere to 10 amperes; resistance

from

test

instrument include the use of precision

is a completely portable,

will

measure rms values of

from

0.005

—20 db to +50 db. Input

with

movement. The panel has been specially designed

simplified

—DC

leads—a feature

silicon

diodes are used to protect the meter movement

that

operation.*

with

AC,

+DC, and —DC

positions of this switch reverse the polarity

is also

helpful

in checking the front-to-back

with

is completely portable, requiring no external power

internal batteries (not provided) are used for the ohms function

"D"-size

with

a rugged, lightweight, bakelite case.

flashlight

cell).

The unit weighs

SVs

inches. Convenient

test

leads. The

only

WV-38A

3V2

^Included

serial

on

numbers

1—Red Test

1—Slip-on

Boot

WG-297
WG-210

WG-211

WG-270A

Alligator

1—Warranty - Registration

High
Resistor 900

Resistor 495

Vinyl

wired

instruments

above

Lead

66,000

and Probe 1—Black Test

Clip

Available

Voltage Probe

V.

range)

V.

range)

Carrying

with

K.

Items

and Red

serial

Supplied

numbers

with

Clip

1—Instruction

(Batteries Not Supplied)

Accessories

Megohm

Megohm

for H.V. Probe (10 x

for

H.V.

for WV-38A

Probe (100 x

Case

above

WV38A

and

20,000,

Lead

Black

Book

multiplier

multiplier

and on

with

Boot

kits

with

Alligator

Card

for 5000

for 250

3

DC

Voltmeter

(at

full

RCA

Volt-Ohm-Milliammeter

Specifications

Electrical

scale) :

Ranges

0 to

.25,

1.0,

2.5, 10, 50, 250, 1000, 5000 volts
Input resistance 20,000 ohms-per-volt
Circuit
Accuracy

AC

Voltmeter

Ranges

loading

50

microamperes bleeder current

±3%

(at

full

scale) :

..

.."

.. .0 to

2.5,

10, 50,

250, 1000, 5000 volts
Input Resistance 5000 ohms-per-volt
Circuit

Accuracy

DC

Current

¥?o«Mo

Kanges••

Insertion

Accuracy

DC

Ohms:

R

X1 0-2000 12 ohms

R

X100 0-200,000 1200 ohms

R X 10,000 0-20,000,000 120,000 ohms
Accuracy

loading 200 microamperes bleeder current

±5%

Frequency

from

10 cps to 50 kc on the 2.5, 10, and 50

(at

1 0 to

Response (reference 1000 cps) flat

full

scale) :

' " " ^ 0 to 100

Loss

.0.25

within

volt

0

to

0

to

*4 db

ranges.

50 microamperes
1 milliampere
10 milliamperes

milliamperes

0

to

500 milliamperes

0

to

10

amperes

±3%

Ranges

Scale Ends Center Scale

120

Full

MA

Scale Currents

MA

±3° of

0.06

pointer position

MA

for

exact value

volt

Internal

AF

Output

Batteries:

RX1
R X 100

SizeD

Size D Cell,

R X 10,000

(at

Ranges

0 to

. .4

full

scale) :

Input Resistance 5000 ohms-per-volt
Circuit
Accuracy

Note

:

An

put

measurements

Loading

200

±5%

internally connected

in

4

Penlite

0.1

presence

Cells

*if DC

of DC

in

series

blocking

voltages.

Cell,

1%

volts

iy2 volts

with D cell,

7%

volts

2.5, 10, 50, 250 volts
microamperes

capacitor permits out-

RCA

Volt-Ohm-Milliammeter

Decibel

Dimensions—(less

used when measuring Ohms. The second black scale is used to read DC
voltages and currents. The two red scales are used when measuring AC
voltages, the lower one being used
scale on the meter is used for decibel measurements. A chart, located
at the lower right hand corner of the scale for convenience, is used when
making

Levels

2.5 V, range
10 V. range
50 V. range
250 V. range

(Zero

(May

DB is 1

be read on Output or AC positions)

Mechanical

handle)

Height

Width

Depth
Weight

There are

decibel measurements.

five

separate

milliwatt

in 600

ohms)

:

-20 to +10 DB

-

8to+22DB
+ 6to+36DB
+20 to +50 DB

Specifications

.

6% inches

. 5x/4

inches

:3Y$

inches

3l/2 pounds

Meter

scales on the meter. The top black scale is

Scales

only

for the 2.5 V. range. The bottom

Range

The

Range

12 positions. The Range

obtain

the function and range desired.

Switch,

located at the center of the control panel, has

Switch

Function

The

Function

has

three
switch
must be set to the "+DC" position.

9

The
"+" jacks, permitting direct measurement of negative direct current and
DC

voltage.
reversing
resistance ratio of electrolytic capacitors and many types of semiconductor
devices.

positions,

To

measure all AC Voltages and to make decibel measurements, the

must be set to the

For

positive direct current and DC voltage measurements, the switch

"—DC"

This

the polarity of the

Switch

"AC",

position reverses the polarity of the
switch position can also be used as a convenient means of

located at the upper left-hand corner of the panel

"+DC",

"AC"

position.

test

Switch

may be turned in either direction to

Switch

and

"—DC".

"—COMMON"

leads when checking the front-to-back

and

RCA

Volt-Ohm-Milliammeter

Operating

Zero

The pointer of the meter must indicate zero when the
the normal operating position. If the pointer
adjustment screw located at the lower center of the meter cover should

be readjusted.

Use of

The meter scales on the
ease

of operation and quick readability over a wide
ments. Scales have been grouped according to the type of measurement
for

which

the

WV-38A,

on

two
measurements, always use the
reading
Volts
the 50
50

Volt

obtained. This general rule applies to all AC and DC Voltage ranges.

For

resistance measurements, however, the

one

which

WV-38A

factor

plication

when

ment, the 0 to 10 scale is used, but the reading is

they are used.

Because of the wide number of measurement

it is often possible to take voltage or resistance readings

ranges

which

can be read from either the 50

Volt

range

provides the most accurate Ohms readings at mid-scale points.

For

some

with

is indicated by the setting of the

the

range

and scales. For

is

nearest

range

provides a reading

the scale to obtain the correct reading. The required

will

provide a reading

only should be used if a reading of

measurements

switch is set to the 1000 V. position for voltage measure-

Setting

Range

WV-38A

greatest

range

to the full-scale point. For example: 48 DC

nearest

it

will

Section

of

Pointer

does

and Meter

have been designed to provide

accuracy in voltage and current

which

Volt

or the 250

nearest

range

the center of the scale,

be necessary to use a

range

not indicate Zero, the

Scales

ranges

will

provide an on-scale

Volt

the full-scale point, the

best

selected should be the

switch. For example:

multiplied

WV-38A

range

of measure-

provided on

range. Because

accuracy is to be

because

multiplying

by 100 times.

is in

the

multi-

CAUTION:

When
to make a
ered necessary,
ment or impair the accuracy of indications.

It is also good practice for personal protection to turn off all power

to the circuit under

The power to the circuit under

resistance
may result.

6

making voltage or current measurements, it is good practice
trial

measurements

measurement at a higher

because

repeated overload may destroy the meter move-

test

when connecting or disconnecting the

are made, otherwise damage to the

range

test

must be turned off when

setting than is consid-

test

leads.

in-circuit

WV-38A

RCA

Volt-Ohm-Milliammeter

Figure 1. D-C Voltage Measurement

DC

Voltage

1. Set the

2.

Set the Range Switch to a position considerably higher than the

voltage to be measured.

3. Plug the black
panel.

4. Plug the red
the 2.5 V., 10 V,, 50 V., 250 V. or 1000 V.,

5. Connect the

6. Reset the Range Switch to a position w ^ gives a suitable pointer

deflection.

7. Read the DC voltage from f1 scale corresponding to the
selected.

Note:

In

be

Special

Note:

When using the .25 V and 1 V jacks, the Function Switch

8. To use the .25 volt

and plug the red

9. To use the 1 volt

and plug the red

10.

To use the 5000 volt

tion,

AC-DC

rare

applications where high energy rf is

ing

dc "keep-alive" voltage on TR

necessary

Switch to the "+DC" or

test

test

test

leads

to disconnect meter-protection diodes CR3 and CR4.

.25 Volt, 1 Volt, and

set to the "+DC" position. Meter polarity
applying
test

and plug the red

the red

lead to the negative circuit point.

Measurement

lead into the

lead into the "+" jack on the control panel when

to the voltage sourc** ^ be measured.

"— COMMON"

5000

test

lead to the positive circuit point and the black

range,

test

range,

test

set the Range Switch to the ".25" position,

lead into the "+.25

set the Range Switch to the "1.0 V" position,

lead into the "+1 V" jack.

range,

test

set the Range Switch to the 5000 V posi-

lead into the "DC 5

(See Fig* 1.)

"—DC"

tubes

Volt

V/50/*A"

in

position as required.

jack on the control

range

present,

radar

is used.

equipment, it may

Ranges

must

jack.

KV"

range

such as

be observed by

jack.

measur-

must

be

RCA

Volt-Ohm-Milliammeter

Figure 2. A-C Voltage Measurement

AC

Voltage

1. Set the

2.

Set the Range Switch to a position considerably higher than the

voltage to be measured.

3. Plug the black
panel,

4. Plug the red
the 2.5 V, 10 V, 50 V, 250 V, or 1000 V
V

range

jack.

5. Connect the

6. Reset the Range Switch to a position which gives a suitable pointer

deflection.

7. Read the AC voltage from the scale corresponding to the
selected.

AC-DC

is used, the red

Switch to the

test

test

lead into the "+" jack on the control panel when

test

leads

Measurement

"AC"

lead into the

test

to the voltage source to be measured.

"-COMMON"

lead

must

(See Fig. 2.)

position.

jack on the control

range

be plugged into the

is used. When the 5000

"AC5KV"

range

8

RCA

Volt-Ohm-Milliammeter

Figure 3. D-C Current Measurements

DC

Current

1. Set the

2.

Set the Range Switch to a position considerably higher than the cur-

rent

3. Plug the black
panel for all

4. Plug the red
ranges

5. Connect the

6. Reset the Range Switch to a position which gives a suitable pointer
deflection.

7. Read the DC current from the scale corresponding to the
selected.

8. To use the 50/iA
and the Function Switch to "+DC". Plug the red
"4-.25
red
to the negative connection.

9. To use the 10
and the red
AC-DC
set to the 10A position. Meter polarity
the red
lead to the

AC-DC

to be measured.

with the exception of the 10A and 50/iA

V/50/*A"

test

lead to the most positive current connection and the black lead

Switch

test

Switch to the "+DC" or

test

ranges

test

lead into the "+" jack on the control panel for all

test

leads

range,

jack. Meter polarity

AMP

test

lead into the "+10A" jack. On this current

must

lead to the most positive circuit connection and the black

other

circuit connection.

Measurement

lead into the
with the exception of the 10

in

series

set the Range Switch to the "50aA" position,

range

be set to the

plug the black

"—COMMON"

with the current

must

"-f

DC

(See Fig. 3.)

"—DC"

be observed by applying the

test

lead into the

position, and the Range Switch
must

be observed by applying

position as required.

jack on the control

AMPS

ranges.

flow

range.

to be measured.

range

test

lead into the

"—10A"

range

jack,

the

RCA

Volt-Ohm-Milliammeter

Ohms

1. Set the Function

2.

Set the Range

3.

Plug

the black

Switch

test

Figure

Switch

4. DC Ohms Measurement

Measurement ( See Fig. 4.)

to the "+DC" position.

to the appropriate position.

lead into the

"—COMMON"

jack on the control

panel.

4.

Plug

5. Short the

6. Connect the

7. Reset the Range

8. Read the resistance

the red

until

the pointer indicates "0"

test

lead into the " + " jack on the control panel.

test

leads together and adjust the

(full

scale

test

leads to the resistance to be measured.

Switch

if necessary to a position

clockwise).

able pointer deflection. If this is necessary,

before proceeding

with

from

step

the

8.
OHMS

scale, and

ZERO OHMS

which

repeat

multiply

gives a suit-

steps

by the range

control

5 and 6

factor.

CAUTION:

Low-current, low-resistance devices, such as thermo­couples and meter movements, may be damaged unless a range above
"R XI"

is used, because the

WV-38A

applies up to 1.5 volts across the

resistance under measurement when the range selector is set at "R X 1".

To

facilitate checking the front-to-back resistance ratio of electrolytic
capacitors and semiconductor devices, the
simply

by setting the Function

Switch

test

to the

lead polarity can be reversed
"—DC"

position.

10

RCA

Volt-Ohm-Milliammeter

Figure 5. Decibel Measurement

AF

Output

1. Set the Function Switch to the

2.

Set the Range Switch to a position considerably higher than the

decibel

3. Plug the black
panel.

4. Plug the red
panel.

5. Connect the

6. Reset the Range Switch to a position which gives a suitable pointer
deflection.

7. Read the decibel
using the 2.5 V.

refer to the
meter
indication

measurement

scale, for the decibel factor

for the proper decibel

(Decibel)

test

test

lead into the

test

leads

measurement

range.

chart

Measurement

"AC"

to be

lead into the

to the AC source to be measured.

located at the lower right hand corner of the

made.

When using the 10 V, 50 V, or 250 V

position.

"—COMMON"

"OUTPUT"

directly from the DB scale when

that

measurement.

must

(See Fig. -5.)

jack on the control

jack on the control

range

be added to the

meter

RCA

Volt-Ohm-Milliammeter

Figure

6. WG-297 High Voltage Probe

Accessory High-Voltage Probe

(Available

The

WG-297

resistor, as illustrated in Fig, 6, extends the DC rating of the
to a maximum of 50,000 volts for use in high-impedance circuits. The
WG-210

multiplies
DC.)
of

495 megohms, multiplies the 250 V. DC
times. (I.E. 25,000 V. DC.) These probes and multiplier combinations
make possible

other high-impedance circuits having inherently poor regulation.

Multiplier

the 5000 V. DC

Similarly

High-Voltage Probe, in combination

Resistor,

the

WG-211A

measurements

on

Separate

which

range

multiplier resistor,

in TV high-voltage power supplies and

has a resistance of 900 megohms,

by a factor of 10 times. (I.E. 50,000 V.

Order)

which

range

with

a multiplier

WV-38A

has a resistance

by a factor of 100

Applications

The

WV-38A

of

electrical and electronic circuits. It

current, and the resistance of all DC circuits. For AC circuits, the
measurement is indicated as

ranges
of
WV-38A.
use of the output circuit, and the DC voltage can be measured directly
through the DC voltage circuit.

are based on a zero

a mixed AC and DC voltage can be measured separately

The AC voltage can be measured

is designed to

level

measure

R.M.S.

of 1

milliwatt

the significant characteristics

will

measure

volts or decibels. The decibel

in 600 ohms. Either

individually

the voltage, the

part

with

through the

the

RCA

Volt-Ohm-Milliammeter

Checking

The

R X 10,000
capacitor leakage resistance. A good paper or
1 id

will

indicate above the 20 megohm mark
surge required to charge the capacitor is completed. If the resistance
indicated

insulation.
the capacity. The

and the longer it

is

shorted, the pointer
open,
will

indicate
Electrolytic
charging.
and voltage rating. For example, a low voltage, high capacitance unit
will

indicate more leakage (lower resistance) than a high-voltage, low
capacitance unit. When testing an electrolytic capacitor, the red lead
must be connected to the positive and the black lead to the negative

terminal

must be in the "+DC" position.

is less than 20 meg., the capacitor probably has defective

The time required to charge the capacitor

there

will

only

capacitors, however, normally indicate some leakage, after

The amount of leakage is generally related to the capacitance

of the capacitor, and the function switch on the

range

greater

will

be no

a slight deflection and a rapid return to

of the

the capacity, the more the pointer

take for it to return to

will

not return to

initial

pointer deflection.

Checking

The

resistance of copper oxide, selenium,

fiers

can

be measured in both directions. The resistance measured
should
direction.
setting the Function
polarity

be quite large in one direction and very

The front-to-back resistance ratio can be checked easily by

of the

test

Switch

leads.

from

Capacitors

WV-38A

permits some indication of

infinity.

Rectifiers

"+DC" to

mica

("2K")

infinity.

Very

silicon

small

"—DC",

capacitor under

after the

will

If the capacitor

If the capacitor is

small

and crystal recti-

in the opposite

thus

reversing the

initial

vary

will

capacitors

with

swing

infinity.

WV-38A

Use of an

In

certain sensitive circuits in radio and TV receivers and other

I.F.

or R.F. high-gain amplifiers, it is not possible to connect leads
without
voltage
with
when

stituted, if a resistor is used in series

the end of the red probe. If an exact measurement is not required, almost

any value of resistor, higher than the
instrument so it
measurement has to be made, a resistor should be used
multiplies
can

values of resistors to be used:

disturbing the normal operation of the circuits.

measurements

a resistor-isolation probe, such as an RCA

the

VoltOhmyst

will

the input resistance of the instrument so

be made on one of the higher scales. The

Range

Resistor Reading Multiplier Scale to Read

2.5 V 50 K 2 X 5 V

2.5 V 150 K 4 X 10 V
50 V 1 Meg. 2 X 100 V

250 V 5 Meg. 2 X 500 V

in such circuits requires the use of a

is not available, the

not overly disturb the

Isolation

with

circuit

Resistor

VoltOhmyst.

WV-38A

the instrument,

impedence,

circuit.

following

will

When an exact

that

Usually,

However,

can be sub-

clipped

isolate the

which

the reading

table gives

DC

VTVM

onto

exactly

RCA

Volt-Ohm-Milliammeter

WV-38A

Circuit

Description

VOM

Metering Circuit

The

WV-38A
rent functions consists of the calibrating potentiometer R22, connected in
series

R25,
CR4)

movement due to accidental overload.

cessively

divider
R3,

rectifier

tained by using a voltage-divider network. The resistors in this network are

RIO,

brating

the high AC ranges.

with

the

In

the ohms function, the calibrating potentiometer is replaced by

the front panel

Some

models of the

connected across the meter terminals to prevent damage to the meter

The

eight
higher, values of resistors in series

The

.25 V range is connected directly to the meter

network used for the remaining

R4, R5, and R29.

The

diodes CR1 and CR2, along

circuit,

The

six AC voltage ranges, as

Rll, R12, R13, R14, and R28. R24 is a 6K potentiometer for

the low AC ranges. R23, also a 6K potentiometer, is for calibrating

meter

50/xA

ranges

converting the AC signal input to pulsating DC voltage.

circuit

meter movement.

ZERO

WV-38A

of the DC volts

for the AC

OHMS

have two special

DC

AC

control.

Volts

Volts

with

Volts,

circuit

with

ranges

with

R20 and R21,

the DC voltage section, are ob-

DC

Volts,

silicon

are obtained by adding suc-

the meter

circuit.

is composed of R27, Rl, R2,

and DC cur-

diodes (CR3 and

circuit.

The voltage

form

a full-wave

cali-

DC

Current

The

DC current

values of shunt resistance across the meter

scale deflection. The

Range Series Resistors Shunting Meter

50/iA
1 ma R6, R7, R8, R9, and R26
10 ma R6, R7, R8, and R26
100 ma R7, R8, and R26

500 ma R8 and R26

10 Amp R26

ranges

ranges

No shunt used

are obtained by switching the appropriate

circuit

and shunting resistors are listed below:

to maintain 50/iA

full-

Resistance

In

resistance measurements, the ohms control, R-25, is connected in

series

with

the meter, and is used for calibrating or "zeroing" each range.

In

the R x 1 and R x 100 ranges, the 1.5V "D"

to the

used, resulting in 7.5 volts. The battery voltage is applied to the meter
circuit
are shorted,
deflection.

circuit.

and shunt resistors of the particular range so

In the R x 10,000 range, the four 1.5V penlight cells are also

50/*A

of current

pass

through the meter, causing full-scale

cell

that

battery is applied

when the

test

leads

RCA

Volt-Ohm-Milliammeter

When
the meter
causing

In

and

R19 is shunting the meter

In
cuit,

and R16 and R19, connected in series, shunt the meter

in

series

In
shunting
(7.5V).

The
serves to protect the resistors used for ohms measurement against damage
due to accidental overload.

a resistor is placed across the

will

be reduced in proportion to the value of the resistor,

the pointer to deflect down-scale to the appropriate reading.

the R x 1 range, R16 and R17 are in series

circuit.

the R x 100 range, R17 is connected in series

with

the R x 10,000 range, R16, R17, and R19, connected in series, are

the meter

1 amp fuse is connected in series

the 1.5V battery.

circuit.

R18 is connected in series

test

leads, current

with

the

flow

with

the meter

with

—COMMON

the meter
circuit.

with

the batteries

through

thus

circuit,

cir-

R15 is

jack, and

Maintenance

The

WV-38A
screws
and

from

batteries are removed as a complete unit.

the rear of the case. The meter, panel, laminated

may be removed

from

its case

simply

by removing four

circuit

board

The

need for battery replacement is indicated when the instrument
not zero properly on the Ohms ranges. If it is not possible to zero the R X 1
and

R X 100 ranges, the large "D"
possible
ment. It is generally good practice to replace all batteries when a replacement
is

needed.

above. It is important
as shown in the
with

to zero the R X 10,000 range, the four penlite

The

batteries are installed in the instrument as shown in Figure 7,

that

the batteries are installed

illustration,

the terminals.

and

cell

that

the battery

will

requires replacement. If it is not

cells

require replace-

with

the polarity exactly

clips

make proper contact

RCA

Volt-Ohm-Milliammeter

Resistor

Almost

on

the rear of the laminated
shooting
should
the laminated
the new resistor. The holes may be opened
or
to prevent any short

resistor.

be removed

appropriate probe

all of the resistors contained in the

and repair. When replacing a resistor, the defective resistor

from

circuit

the laminated

board should be opened to accept the lead

while

circuit

the solder is melted. Care should be taken

to any other

Fuse

The

fuse contained in the

Multiplier

ing

voltage to the leads when the Range

"R

X 100" positions).

lead

to the

may

be soldered onto the lead
should
of

insulating sleeving may be placed over the fuse to prevent a short

circuit.

NOTE:

dn

all functions in

resistors against burnout due to accidental misuse (apply-

This

AC-DC

be taken to prevent any short

A burned out fuse

Switch

which

fuse may be replaced by unsoldering the

and

the

Replacement

circuit

board,

circuit

with

part

Replacement

WV-38A

clipping
clipped

will

44—COMMON"

is used to protect the Ohms-

Switch

the other lead. The new fuse

from

circuit,

make the instrument inoperative

WV-38A

which

nearby when replacing the

the defective fuse. Care

and if necessary, a piece

jack is used.

simplifies

board and the holes in

the use of a toothpick

is in the "R

are mounted

trouble-

from

XI"

or

DC

Calibration

If

an accurate DC Current source is available, it is recommended
the calibration potentiometer, R-22, be set using the DC Current function
of

the

WV-38A,

1. Set the Function

2.

Connect the

current source.

3.

Adjust R-22 so

R-22

can also be adjusted using a DC voltage source, as described

below:

1. Set the Function
range.

2.

Connect the

source.

3.

Adjust R-22 so

NOTE:
range. Connect the
indicate

1.57 volts (157 on the 250 scale).

as

follows:

Switch

test

leads

that

Switch

test

leads

that

the meter indicates 2.5 V (full-scale deflection).

A fresh 1.5 V battery can be used to calibrate R-22 on the 2.5 V

test

to

"DC^

from

the meter indicates 1 MA (full-scale deflection).

from

leads to the battery terminals, and adjust R-22 to

to

the

"DC"

the

and the Range

"—COM"

and the Range

"—COM"

and jacks to a 2.5 V DC

Switch

and "+" jacks to a 1 Ma

Switch

to "1 MA."

to the "2.5 V"

that

16

RCA

Volt-Ohm-Milliammeter

Rectifier

There are two small rectifiers located at the top of the laminated

circuit

will

placing

rectifier
proper polarity, and the AC voltage

adjusting variable resistors "R23" and

ranges

board. If either, or both rectifiers become defective, the

give incorrect indications when measuring AC voltages. When re-

a rectifier, be

before removing. The new rectifier must be replaced in the

of the

WV-38A,

sure

proceed as

AC

1. Set the

2.

Set the Range Switch to the "250 V" position.

3.

Connect the

4. Adjust variable resistor "R23"

5. Remove the

6. Set the Range Switch to the "2.5 V" position.

7. Connect the

8. Adjust variable Resistor "R24"

9.

Remove the

AC-DC

test

test

test

test

Switch to the

leads to a known AC voltage source of 250 V AC.

leads from the 250 volt AC source.

leads to a known AC voltage source of 2.5 V AC.

leads from the 2.5 V AC source.

Replacement

WV-38A

to observe the polarity of the defective

ranges

"R24."

follows:

must be recalibrated by

To recalibrate the AC

Calibration

"AC"

until

until

position.

the

meter

the

meter

indicates

indicates

full

full

scale.

scale.

Removing

When
laminated circuit board or to the
front panel; the laminated circuit board must be removed. To remove
the laminated circuit board, proceed as

1. Set the Range Switch to the "2.5 V" position.

2.

Remove the knobs from the

control

3.

Remove the knob from the Range Switch by loosening the set

screw. DO NOT turn switch from its position.

4. Remove the
circuit

5. Remove the two hex

6. Remove laminated circuit board, observing copper rings placed
between the board and the

copper rings as they function as the contacts from the laminated
circuit
that

board and the
properly.
"AP5KV"

it is necessary to gain

by

pulling.

three

board onto the panel posts.

board to the

the copper rings are placed between the laminated circuit

meter,

Also

and

dress

DC5KV"

the

Laminated

access

parts

AC-DC

self-tapping screws which hold the laminated

nuts

meter.

and washers from the

meter.

When replacing the board, make certain

otherwise, the

the interconnecting leads away from the

eyelets and resistors.

Circuit Board

to the under-side of the

located between it and the

follows:

Switch and the

DO NOT lose or misplace

WV-38A will

ZERO OHMS

meter

studs.

not function

these

:RCA

Volt-Ohm-Milliammeter

When

ordering

instrument

Symbol

No.

Rl
R2
R3

R4

R5

R6

R7
R8
R9

R10
Rll
R12
R13
R14
R15
R16
R17
R18

R19
R20
R21
R22,

R23,

R24

R25

R26

R27

R28

R29

Ml

CI

Replacement

WV-38A

replacement

type.

Parts without stock numbers are standard catalog

All

parts should

Description

Resistors

45K

Ohms

1%

150K Ohms
800K Ohms
4

Megohms

15

Megohms

22.5

Ohms

2.0

Ohms

0.452

Ohms

238

Ohms

6200

Ohms
37500
200K Ohms
1

Megohms

3.75

Megohms

110

Ohms

1138

Ohms

21.85K

117.7K

11.5 Ohms.
5K

1% %W 209637

5K

1% %W 209637

Variable

Variable

Shunt Assy.
15K

Ohms

20

Megohms

80

Megohms

Meter

17c %W

1% y2W 93843

1% %W 218881

1% 1W 99317

1% 1W

1% 1W

1% 1W

1% %W 218806

1% V2W 236084

Ohms

1% V2W 218809

1% %W 56733

1% %W 208022

1% %W 237613

1% %W 218807

1% y2W 218808

1% y2W 218810

1% 1W (green) 218814

6000

10,000

10

\% %W 97761

1% 2W 218816

1% 2W

Meter

50

Microamperes

cluding plastic

scale

218818

Capacitor

Capacitor

0.1

parts,

%W

......

(blue).

(yellow).

1% 1W .... 218880

Ohms

225351

Ohms

AMP

case and

MFD 400V

Volt-Ohm

include

be

S^k

56483-A"

(red).

.... 219488

..... 219489

......

in-

the

ordered

217743,

218815
218813

218812

218817

stock

from

Symbol

CR1,
CR2
CR3,

CR4

Fl

Bl
B2

SI
S2

Parts List

Milliammeter

number

your

No.

and

description

items.

local

RCA

distributor.

Description

Crystal

Crystal

Diode Type IN87.

Diode

Fuse Pigtail

250V

212492

Batteries

Type

D 1.5V

Type

A 1.5V

Switches

Range Switch
Function

Switch

Miscellaneous

Panel—with

assembly

Case—(less

assembly)

Handle—(including clips

and

hardware)

Printed

circuit board

(less

parts)

Battery holder

for penlight
Penlight Battery
Flashlight Battery

Test Leads

Red,

with probe

Black

Meter
Knob

Knob
Knob

221712

case,

front

and
pointer 1 inch
small with mark
small

Screw—Handle

Clip—Lead

(on

handle)

Probe—Red

and

Tip 219107

of the

Rectifier

part,

the

Stock

No.

230099

230125

Fuse

3AG 1

AMP

VS-036
VS-034

218877

218876

eyelet

218994

handle

218993

219092

219091

(U

shaped

cells) 219179

Clip

Clip^.

. 219178

221711

plastic,

rear

218995

... 213831

.. 219486

no

mark

... 219487

mtg 219093

Holder

219094

Probe

Information furnished
responsibility
or

other rights

by implication

is

assumed

of

or

by

RCA

by

RCA

third parties which

otherwise

under

18

is

believed

to be

accurate

for its use; nor for any

may

result from

any

patent

or

patent

and

reliable. However,

infringements

of patents

its use. No license is

rights

of

RCA.

no

granted

he

ck

i.

99
25

92

36
34

77
76

94
93
92
91
79
78

11
L2

)5
31
86
87
93

94
07

-COMMON

Ft

1

AMP.

1

Bt

1.5V
1000VOC

250VDC

50

VDC

10V

DC

2.5V

DC

+

10A -10A

NOTES:-

1.

S1

SWITCH POSITIONS-MARKED

ON

SIA DRAWING

R27

_

15K

+iv

DCQ V\Ar

POSITION

RANGE

1

1000V/5000V

2

250

V

3

50V

(.25V,

IV,

50JJA)

4

10V

5

2.5V

6

500

MA

7

100

MA

8

10MA

(10A)

9

1

MA

10

R X 1

11

R

X100

12

R X 10000

+

.25V/50JJA

DCQ-

OUTPUT

o

AC5KV

O

DC

5KV

o

-

ct

*

.1

MFD

R28

>

20

MEG

2W

O

R29

SO

MEG

2W

tOOOVAC

CR3

+ / M1 \

50

jJA

CR4

H4-

.

R22

) 6K/

CAL

2. ALL SWITCH WAFERS SHOWN AS VIEWED

FROM

FRONT

(SHAFT

END

OF

SWITCH)

3.

S1 SHOWN IN POSITION #1

4. S2 SHOWN IN W+DCH POSITION

5. SWITCH

CONTACTS

SHORT

ARROWS INDICATE WIPER CONNECTION

LONG

ARROWS INDICATE

CENTER

RING

CONNECTION.

6. ALL RESISTORS '/2

WATT,

±1%

UNLESS OTHERWISE

NOTED.

,

R15

110

< R18

117.7

K

If)

ts

id

Schematic

WV-38A

NOTE:

In

some

instruments

RIO is

7.5

K, and R22, R23 and

R24

are 4 K.

ItC/1

Printed

in

U.S.A.