Section V. VAP-AIR MODEL 26440001-05
(3) Place positive probe to the bottom side
of CR3. Meter should indicate low resistance.
regulator with the cover off. Figure 218 is the
(4) Reverse probes. Meter should indicate
end view of the regulator showing the receptacles
and the voltage adjustment point. Figure 2-19 is
(5) If other readings are obtained replace
an exploded view of the diode mounting. Figure
diode CR3 (MR1122), NSN 5961-00-103-1519
(see fig. 2-19).
is a view of the circuit board and transistor heat
sink. Figure 222 is a view of the circuit board
showing the electrical test points. There are 12
electrical test points. Figure 223 is an electrical
terminals (see fig. 220 ). Meter should read ap-
schematic diagram of the regulator. Table 28
proximately 60 ohms.
lists the resistance checks. Table 2-9 lists the
(2) Place ohmmeter probes across contactor
voltage checks. Table 2-10 is a transistor substi-
terminals (see fig. 220). Meter should read
infinity (open circuit ).
(3) If other readings are obtained, replace
2-11. Checkout and Repair.
relay, Vap-Air part number 27124377, NSN 2920-
a. Voltage Adjustment Rheostat (R2) (power
(4) Reinstall transistor and circuit board
(1) Place ohmmeter test probes to the violet
and brown wire terminals of the rheostat (see
e. Detailed Circuit Checks.
(2) Rotate rheostat fully clockwise, reading
ance checks of the circuit (see fig. 222 for test
should be approximately 250 ohms.
(3) Rotate rheostat fully counterclockwise,
(2) Table 29 contains "power on" voltage
reading should be less than 5 ohms.
checks of the circuit (see fig. 222 for test points).
(4) If other readings are obtained, replace
f. Functional Checks. Check the performance
of the regulator on the test stand and make final
voltage adjustments. Voltage output should read
(1) Remove transistors Q4 and Q5 (see fig.
28 volts. If the regulator does not function prop-
erly, perform the following:
(1) Check wires and connections.
(2) Position transistors as shown in figure
( 2 ) Replace circuit board, Vap-Air part
( 3 ) If resistance values differ from the
(3) Perform bench test procedures.
above, replace the transistors through cannibaliza-
tion or requisition transistor Q4, Vap-Air part
number 26316033-12 (2N3441), NSN 5961-00
054-4141, or transistor Q5, Vap-Air part num-
After final repair, check regulator on
ber 2631603370 (2N3773), NSN 5961-00929
the test stand.
5014 (see table 210 for substitutes).
If the regulator still does not function correctly
(4) Check the mica insulating washers be-
it will be necessary, if local skills permit, to test
tween the transistors and mounting plate. Re-
each component. All the parts should be checked
place if cracked, broken or missing. Coat washers
with an ohmmeter and the capacitors checked with
with insulation compound per MIL-S-8660, NSN
a capacitance meter. The circuit board traces
should be checked with an ohmmeter to make
sure that there are no cracked traces. Traces with
(1) Remove four screws holding transistor
hairline cracks will show good at lower tempera-
and circuit board mounting plate, and move plate
tures and will tend to show open circuit at higher
to one side.
temperatures. If the board seems good at room
temperature, but the regulator still fails, this
(2) Place negative ohmmeter probe to the
could be the cause.
top side of diode CR3 (see fig. 2-19).