Section IV. GENERAL SUPPORT MAINTENANCE OF TEST SET

TM 11-6625-539-14-4

circuit function

Figure No.

functions fail to operate, check for defective power

Regulated power supply

5-2

supply circuits or a defective meter circuit, because

Beta function circuit

5-3

all functions require the operation of these

Ohms function circuit

5-4

circuits.

FET test circuit

5-5

b. If partial operation of the unit is possible, run

ICES function test circuit

5-6

through a complete checkout of all functions to

ICO IR function test circuit

5-7

determine which are faulty. When faulty functions

have been isolated, a check of simplified schematic

d. If the square-wave output is questionable, use

diagrams will indicate common components that

an oscilloscope to check the waveform at the base

are used in the defective circuits, thereby helping

of transistor Q1 or Q2. The square wave must have

to isolate the fault.

approximately 2.5-volt amplitude peak to peak in

c. Following is a list of circuit diagrams related to

the beta function.

the various functions of the test set. Relate these

e. Faulty operation of the test set may be caused

circuits to the major schematic diagram given in

by improper calibration. If the unit gives consis-

figure F0-2 to determine their interoperation in

tently incorrect readings in one or more functions,

the test set.

calibrate the test set as directed in paragraph 7-8.

Section IV. GENERAL SUPPORT MAINTENANCE OF TEST SET

7-8. Adjustustments

a. General. Adjustment of the test set requires

R6 (8, fig. 7-1) to provide a multimeter indication

of 1 mA. Remove the NPN transistor.

that you adjust five variable resistors mounted

(3) Set POLARITY switch to PNP. Connect a

on the back of the test set printed circuit board.

multimeter adjusted to read milliamperes and a

Remove the front panel from the case (para 7-9 to

good PNP transistor to the transistor test set as

provide access to the variable resistors. Main-

shown in figure 7-2. Adjust variable resistor R3

tain the connection between the battery power

(7, fig. 7-2) to provide a multimeter reading of 1

supply and the connector pins on the printed

mA.

circuit board, because the test set must be

(4) This completes beta adjustment. Remove

energized during the adjustment procedure.

the transistor and the multimeter from the test

Refer to table 7-1 for the required tools and

set.

equipment.

d. Offset Adjustment.

b. Battery Check. With the POLARITY switch

(1) Set FUNCTION switch to BETA position,

in the OFF position, operate and hold BAT CHK

the POLARITY switch to PNP, and the RANGE

switch in the direction of the arrow. Check to see

switch to X 0.1.

that the meter pointer deflects into the BAT

(2) Connect a good PNP transistor directly

CHK range on the scale (red).

into the transistor socket on the panel of the test

c. Beta Adjustments.

set. Connect a multimeter adjusted to read

(1) Set the FUNCTION SWITCH to BETA.

millivolts into the remote test jacks C, D and E, S.

Set the POLARITY switch to NPN. Set the

(3) Adjust variable resistor R8 (9, fig. 7-1) to

RANGE switch to X 0.1.

obtain a zero voltage indication on the multime-

(2) Connect a multimeter adjusted to read

ter (if analog) or 0.0 (if digital).

milliamperes and a good NPN transistor test set

as shown in figure 7-2. Adjust variable resistor

7-2

Change 1