Marantz 5220 User Manual download pdf (Page 54)

CONSTRUCTION

SAMUEL

LYLE

CURVE TRACER

Checks

Semiconductor Quality

from

Breakdown

Voltage

to Beta

ASIMPLE go /no

-go

tester

will

tell

you

a transistor will

operate, but

it will not

tell

you

the

quality of opera-

tion.

For

this,

you

need

a curve tracer,

which

usually an adapter designed

be used with an

oscilloscope.

The

Experimenter's Assistant

tracer /tester

described here

can

test virtually

any

type

of discrete semiconductor de-

vice,

classify

according

to type

(npn

pnp)

and

material

(silicon

ger-

manium),

and check

reverse

and for-

ward

breakdown

voltages

and

leak-

age.

can also

provide

a rough indica-

tion

of a

transistor's

beta.

In addition to

semiconductor de-

vices, the tester

can also check

capacitors and

inductors.

With a little

imagination,

can

also be used for

in-

circuit testing.

To make testing

conditions as safe as possible, the

maximum test

current

is limited to

slightly

less than 4 mA.

Circuit Operation. The tester pro-

vides

a simple

means

of depicting the

voltage

/current

behavior characteris-

tic

the

component under test,

graphically

displaying the characteris-

tic

oscilloscope screen.

The

basic circuit

shown

in Fig. 1

consists

transformer

Tl,

resistors

R1 and

R2,

switch

Si,

and

component attach-

ment jacks

and

J2.

Note the three

connections that must

made from

the tester to the

oscilloscope's

hori-

zontal and vertical inputs

and

ground.

The

remainder

the

circuit

used

for

actual semiconductor testing

and

connected

the basic circuit by

plugging

into

and P2 into

J2.

With Si open, the 12.6 volts rms

Tl 's secondary provides the sweep

for

the scope. Because the input impe-

dance of

the

scope

is virtually infinite,

relative to the value

of R1, the

full

transformer

swing of

±17.82 volts

peak -to

-peak

applied

to the horizon-

tal input

the

scope. Since

effec-

tive

current

flows through

R1, no sig-

nal

appears

the

scope's

vertical in-

put.

The result is

horizontal

trace on

the

CRT,

with the right

and

left

ends of

the trace representing +17.82

and

-17.82 volts, respectively.

test

leads

are connected to

J1 and

and

their test tips

are shorted to-

gether,

the full

secondary

voltage

will appear across R1, while no

voltage

applied to

the

scope's

hori-

J3 J4 J5

A typical

layout

for

the

curve tracer.

zontal input. This results in

vertical

trace

the

CRT,

with the top

of the

trace representing

a current

of 3.8

(17.82 volts

/4800

ohms = 3.8

mA).

Removing the

short between the

test leads

and depressing Si places

R1 and R2 in the

circuit.

Now, the

scope will display

45° trace,

assum-

ing

the horizontal and vertical input

channel gains

the

scope are prop-

erly set.

Resistor

R2 and switch Si are

used for balancing the

channel

gains.

Once

the

channel

gains have

been set

display a

45°

trace, any

component

whose resistance is

greater than

4700

ohms

will produce

more nearly hori-

zontal trace, while

component

resist-

ances

less than 4700

ohms will

pro-

duce a

more nearly vertical trace. The

actual

slope of

the trace is directly re-

lated

to R1!R.,F; -,,

where

R1 =

4700

ohms

and R

, EST

is the resistance

the

component

connected across the

JIIJ2

test probes.

Construction.

You can assemble

the

tester

any enclosure of

convenient

size using

a point -to

-point

wiring

technique. Use a

terminal strip to

mount the five resistors.

The

best

place to

mountSOi,

Si, S2, J1,

and

the

cover

of the enclosure.

Connect one end of a

12" (30.5

-cm)

length

of flexible test

lead

to the C

lug

on SO/, tie a

knot in it to

serve

as a

strain

relief, pass the free

end

through

rubber -grommet -lined hole in the

top of

the

case, and

terminate the

cable with a banana or tip

jack (to

mate

with

J1).

Repeat this

procedure

with

a cable connected

to the E

lug

Soi.

These two cables,

when plugged

into

and

J2,

allow transistors plug-

ged

into

SO/ to be tested.

For in-

circuit

tests of transistors and diodes

and

out

-of-

circuit

tests

transistors

that do not fit

into

SOI , separate

test

cables

must

be plugged

intoJi

andJ2.

Prepare these with

appropriate plugs

at one end and standard

test probes at

the

other end.

MountJ3,

J4,

and

J5 on

the rear wall

the case. Prepare three 36" (about

1- meter) test

cables

with plugs

(P3,

P4,

and P5) to

match

these jacks on one

end

and plugs to

match

the

input

con-

nectors

your

scope

at the

other

end.

These last

jacks and cables

are

for interconnecting the tester with a

scope.

Alternatively, you

can connect

the cables directly

to the

appropriate

points

in the tester circuit and

have

them

exit

the

case

through grommet -

lined holes and

eliminateJ3, J4, J5,

P3,

P4, and P5.

After wiring the circuit and assem-

bling the case,

label

the jacks, plugs,

switches,

and test socket.

Using the

Tester. If an "ideal"

diode is connected between

and

J2,

it will act as a short circuit

for

one -half

of the ac cycle

when forward biased.

During the other

half -cycle, it will be

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