Section II. VAP-AIR MODEL 26440001-01

TB 9-2920-225-34-1

Section II. VAP-AIR MODEL 26440001-01

2-4. General. Figures 23 and 24 show two views

(5) If other readings are obtained, replace

diode CR6 (MR1122), NSN 596100-1031519

of the regulator and its parts. Diode and transistor

(see fig. 2-4).

NSNS and parts numbers with substitute NSNS

and part numbers are listed in table 21.

(6) Reinstall transistor mounting plate.

d. Circuit Board. If no faulty components were

2-5. Checkout and Repair.

detected after performance tests a, b, and c above,

a. Voltage Adjustment Rheostat (R6) (power

replace the circuit board.

disconnected).

(1) Remove voltage adjustment access plug

e. Functional Check. Check the performance of

(see fig. 2-3).

the regulator on the test stand and make final

(2) Place ohmmeter test probes to terminals

voltage adjustments. Voltage output should read

of the rheostat (see fig. 2-3).

28 volts. If the regulator does not function prop-

(3) Rotate rheostat fully clockwise; reading

erly, perform the following:

should be less than 5 ohms.

(1) Check wires and connections.

(4) Rotate rheostat fully counterclockwise;

(2) Replace circuit board.

reading should be approximately 2500 ohms.

(3) Perform bench test procedures.

(5) If other readings are obtained, replace

rheostat.

NOTE

b. Transistors.

(1) Carefully remove transistors Q7, Q8, and

After final repair, check regulator on

Q9 (see fig. 2-3).

the test stand.

(2) Position transistor as shown in figure

2-1, and check each separately (see fig. 2-2).

If the regulator still does not function correctly

(3) If resistance values differ from the values

it will be necessary, if local skills permit, to test

shown in figure 22, replace the transistor ac-

each component. All the parts should be checked

cording to table 21.

with an ohmmeter and the capacitors checked

with a capacitance meter. The circuit board traces

NOTE

should be checked with an ohmmeter to make

sure that there are no cracked traces. Traces with

Transistors Q8 and Q9 are identical and

hairline cracks will show good at lower tempera-

c a n be interchanged. Transistors Q7

tures and will tend to show open circuit at higher

must be replaced by a like item in the

temperatures. If the board seems good at room

same socket (see fig. 2-3 ).

temperature, but the regulator still fails, this

(4) Check the mica insulating washer be-

could be the cause.

tween the transistor and mounting plate. Replace

if cracked, broken, or missing. Coat washers with

Table 21. Replacement Parts List--Model 01

insulation compound per MIL-S-8660, NSN 6850

00880-7616.

c. Diode.

(1) Remove four screws holding transistor

mounting plate and move plate to one side.

(2) Place negative ohmmeter probe to the

connector side of diode CR6 (see fig. 23).

(3) Place positive probe to the circiut board

side of CR6. Meter should indicate low resistance.

(4) Reverse probes. Meter should indicate

high resistance.

2-3