Out-of-Circuit Testing of Field Effect Transistors (FET's)

TM 11-6625-539-14-4

necessary, using the METER ZERO control. Re-

(6) Operate the POLARITY switch to EB

lease the toggle switch so that it returns to the

position.

ZERO position and zero the meter using the ICES

(7) Adjust ICES ZERO/OHMS ADJ COARSE

ZERO/OHMS ADJ FINE control.

and FINE controls to indicate infinite reading on

(7) Connect the test leads to the color-matched

OHMS scale of meter. Short together the E-B

remote test jacks. Connect the red lead to the

jacks. Zero the meter using the METER ZERO

collector, the black lead to the base, and the

control. Remove the short and readjust as neces-

yellow lead to the emitter of the device under test.

sary for an infinite reading. Repeat the procedure

as required until zero and infinity are properly

(8) Use the ICES ZERO/OHMS ADJ COARSE

set.

and FINE controls to zero the meter. This will

null the effects of the circuit loading.

(8) Insert the test leads into the panel test

jacks, being sure to match lead and jack color.

(9) Press and hold the ICES toggle switch to

Connect the red lead to the collector, the black

READ and check the indication on the meter. Mul-

lead to the base, and the yellow lead to the

tiply the reading by the setting of the RANGE

emitter of the device under test.

switch. This is the ICES value. Compare this value

(9) Sequentially operate the POLARITY

with that in section II of appendix D. Reject the

transistor if leakage is greater than that listed.

switch from EB to CB to E-C, checking the

(10) Disconnect the test leads from the device

meter deflection at each position on the OHMS

under test. Turn the POLARITY SWTICH TO

scale. These positions indicate resistive load

OFF.

across each portion of the transistor circuit. Re-

sistance across any portion of the circuit shall not

2-11. Out-of-Circuit Testing of Field Effect

be less than 500 ohms. If resistance is less, a

Transistors (FET's)

significant beta reading cannot be made in circuit.

(10) If resistance is greater than 500 ohms at

FET devices are tested for transconductance and

all positions, restore the FUNCTION switch to

the values are given in micromhos (microsiemens)

BETA. Read the value on the BETA scale of the

on the GM scale. Test out of circuit as follows:

meter. If necessary, adjust the RANGE switch to

a. Operate the POLARITY switch to PNP for P-

X 10 and multiply the BETA scale reading by 10.

channel devices or to NPN for N-channel devices.

(11) Check the beta value listed in section II,

CAUTION

appendix D for the device under test. Reject the

transistor if the beta value is less than the value

Insulated gate FET's, denoted by the

given.

letter "I" in the listings is section 111 of

appendix D are prone to destruction by

(12) Disconnect the test leads from the tran-

accumulations of static charge on the

sistor.

gate. Permanent damage will occur if

b. Leakage Test. Make an in-circuit leakage test

gate voltage rating is exceeded even for

as follows:

a short time. When working on these

(1) Operate the POLARITY switch to PNP or

devices, make sure you and all other

NPN, whichever is applicable.

personnel, and all equipment, including

(2) Operate the FUNCTION switch to ICO, IR.

soldering irons, are grounded. When

(3) Adjust the RANGE switch to X 0.1. Check

testing insulated gate FET's, you must

set the POLARITY switch to a setting

for meter zero. If necessary, zero the meter using

r e v e r s e from that used for normal

the METER ZERO control.

FET's.

(4) Adjust the RANGE switch as required by

the value of the device under test as indicated in

b. Operate the FUNCTION switch to FET.

section II of appendix D. Set to:

c. Set the RANGE switch to X 0.1. Check for

X 0.1 for 0 to 10 µA

meter zero. If necessary, zero the meter using the

X 1.0 for 0 to 100 µA

METER ZERO control.

X 10 for 0 to 1.0 mA

d. Set the RANGE switch to X 10.

(5) Operate the FUNCTION switch to ICES and

use the ICES ZERO/OHMS ADJ COARSE and

e. Install the transistor into the transistor

FINE controls to zero the meter in this setting.

socket on the front panel. Be sure that gate,

(6) Press and hold the ICES toggle switch to the

drain, and source leads are respectively inserted

READ position and adjust the meter to zero, if

into G, D, and S sockets. If necessary for lead

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