Out-of-Circuit Transistor Tests

TM 11-6625-667-45/NAVSHIPS 0969-249-8010/NAVAIR 16-30APM123-2/TO 33A1-3-367-22

(11) In-circuit resistance measurements of module A16. Unless specified otherwise, all transistors are

type 2N706. All measurements should be within 50 percent of values shown. Transistor Q3 is not

listed because it is not accessible.

10K

R X 10K

10K

780K

10K

Q1 (2N2222) ---

10K

750K

10K

R X 10K

11K

Q2 (2N2222) ---

700K

10K

680K

10K

R X 10K

10K

RX100

58K

740

A2Q1---------

10K

58K

22K

10K

R X 10K

RX100

10K

720

22K

A2Q2----------

10K

11K

10K

620

RX100

620

10K

11K

A2Q3 (2N1485)-

b. Leakage Test. Connect the transistor and the

3-9. Out-of-Circuit Transistor Tests

TS-352B/U as shown in figure 3-20. The resultant

Perform as many in-circuit tests (para 3-8) as

value should be equal to, or less than, the maxi-

practical before removing wired-in transistors

mum allowable leakage current (I.c o) for that

When a transistor tester is not available an

particular transistor as shown in the Maximum

ohmmeter may be used to test the emitter and col-

leakage

column (d below).

lector diode condition (a below), maximum leak-

Note. Although Multimeter TS-352B/U cannot be

age

(b below), and grounded emitter and

utilized for measuring current as low as 1 microampere

current gain (dc beta) (c below).

any readable deflection in this range can be assumed

Caution: Use only the ohmmeter range speci-

to be in excess of the permissible maximum leakage cur-

fied to avoid transistor damage. Set ohmeter

rent. Since the

reading is also on the low end of the

range before making any connections.

meter scale and similarly difficult to read, any indication

significantly higher (above 20 a) can be assumed to be

a. Emitter and Collector Diode Test. Use the

too great.

chart (d below) in conjunction with figure 3-19,

c. Gain Test. Connect the transistor and ohmme-

to determine the condition of the emitter and col-

ter as shown in figure 3-21. Note the ohmmeter

lector diodes of the transistor under test. Ohmme-

indication. The grounded emitter current gain (dc

ter connections, to measure forward and reverse

beta) can then be computed from the appropriate

resistance of either emitter or collector diodes of

formula below and compared with the values

NPN transistors, are shown in the illustration.

listed in the Minimum gain dc beta column (d

Only NPN-type transistors are used in this equip-

below).

ment. If the needle of the ohmmeter creeps slowly

12,000

Low-power transitions: Dc beta=

toward a lower value while forward or reverse

Ohmmeter reading

High-power transistors: DC beta= 1,200

resistance measurements are being performed, the

Ohmmeter reading

transistor is defective.

Note. A transistor that indicates normal during gain

Caution: If either of the transistor junc-

tests may still have excessive leakage.

tions (diodes) is shorted, as indicated by low

d. Readings. The following chart lists readings

dc resistance of both directions do not perform

taken with the TS-352B/U connected as shown in

the leakage test (b below) as the ohmmeter may

figure 3-19 (resistance), figure 3-20 (leakage, Ico),

be damaged.

and figure 3-21 (gain, dc beta).

3-39