Heathkit IT -3120 - In Case of Difficulty; General Troubleshooting Information

Heathkit IT -3120

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Page

21

2.

Press

the

BAT

TEST

switch.

3.

Press

the

ON-OFF

to

the

ON

(in)

position.

The

meter

pointer

should

fall

within

the

BAT OK mark.

4.

Press

the

NPN-PNP switch

to

the

PNP (in)

position

to

check

the

other

battery.

The

meter

pointer

should

fall

within

the

BAT OK

mark.

5. Release

the

ON-OFF

switch

to

the

OFF

(out)

position.

NOTE: Do

not

leave

the

Tester

in

the

battery

test

position

any

longer

than

necessary

or

the

battery

life will

be

shortened.

TRANSISTOR

TESTING

General

Out-of

-

circuit

beta

(gain)

tests

are

always

quite

accurate,

but

the

accuracy

of

an in-circuit

test

depends

on

the

shunting

resistances

of

the

circuit

in

which

the

transistor

is

being

used.

If

the

transistor

indicates gain

when

tested

in-circuit,

you may

consider

the

transistor

to

be

good.

Leakage

tests

must

always be

made

with

the

transistor

out

of

the

circuit,

since

the

resistance

in

the

circuit

could

cause

an

erroneous

reading.

To

make

a

quick

good

or

bad test,

perform

only

the

beta

test.

TRANSISTORS

Before

you

test

a

transistor,

it

is

helpful,

but

not

necessary,

to

determine

its class (signal,

intermediate

power,

or

power),

and

its

type

(NPN

or

PNP).

The

current

capability

of

a

transistor

is

what

determines

its

class. Both

the

specific

application

and

the

physical size can

be used

to

estimate

the

amount

of

current

that

passes

through

a

transistor.

A

schematic

diagram

is

helpful

in

identifying

the

particular

application.

Transistors

with

small

metal cases

or

plastic cases will usually be classed as signal

devices. Medium size metal cases

and

transistors

with

small

heat

sinks fall

in

the

intermediate

power

class. Power

transistors

are

usually large

and

most

generally used

with

large

heat

sinks. Figure 2

shows

examples

of

each class.

Figure 2

shows

several lead

configurations

for

transistors.

However, since

there

are

other

configurations,

be sure you

know

the

lead

configuration

of

your

transistor

before

you

test

it.

The

schematic

diagram can also

be

used

to

identify

the

transistor

type

(NPN

or

PNP). Drawings A

and

B

of

Figure 3

show

the

symbols

for

both

an

NPN

and

PNP transistor.

Notice

that

the

arrow

on

the

emitter

lead

points

away

from

the

base

in

the

NPN

transistor

and

points

toward

the

base

in

a PNP

transistor.

Also,

an

NPN

transistor

will have a positive

collector-to-emitter

voltage

while

the

PNP

transistor

has a

negative

collector·to-emitter

voltage.

If

you

are

unable

to

determine

the

transistor

type,

proceed

with

the

test.

Special

steps

are

provided

to

identify

the

type.

FET

NPN

COLLECTOR

BAS

eE

(2

E -

['.

II

HER

0

PNP

COLL

ECT

OR

BAS

BE

(2

E +

E, l

lfER

0

N

CHANNEL

P

CHANNEL

D RA IN

D

RA

I N

D

RA

I N

DRAI

N

~;

GA

l~

~;

GAT

GE

~-

GA

IGE

~-

G A IcE

S -

S -

S

+

S +

SO

U

CE

SOU

RCE

SOU

R

CE

SOURC E

G 0

0 0

DIODES

UJT

SlliCON

/

ZENER

N

CHANNEL

P

CHANNEL

GERMANIUM

(uncommon)

BA

5 l 2

BASE

d +

A'! O

OE

CA

1H

OO

[

A

i

~DE

~C

~

HO

DE

E,,\I

TlEE

R

E

~

\I

iT

~_

~~

~

B +

BASE

BA

S E I

o

o

o

Figure 3

SCR

TRIAC

HOI

ANODE

IA

..

OD

EI

GA

TE

ITR

IG-

T

~

G E

RI

G

i$

GA

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CATHODE

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El

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