TTB-9-2920-225-34-1 Regulator Check Out and Repair 100 Amp 2920-00-900-7993 Download
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TB 9-2920-225-34-1 Table 2-4. Substitutes for D1-Model 03 If the regulator still does not function correctly it will be necessary, if local skills permit, to test each component. All the parts should be checked with an ohmmeter and the capacitors checked with a capacitance meter. The circuit board traces should be checked with an ohmmeter to make sure that there are no cracked traces. Traces with hair- line cracks will show good at lower temperatures and will tend to show open circuit at higher tem- peratures. If the board seems good at room tem- perature, but the regulator still fails, this could be the cause. Section IV. VAP-AIR MODEL 26440001-04 2-8. General. Figure 2-10 is a plan view of the regulator with the cover off. Figure 2-11 is an end view of the regulator showing the receptacles and the voltage adjustment points. Figure 2–12 is an exploded view of the diode mounting. Figure 2–13 is a relay location. Figure 2–14 is a view of the circuit board and transistor heat sink. Figure 2–15 is a view of the circuit board showing the electrical test points. There are 12 electrical test points. Figure 2–16 is an electrical schematic dia- gram of the regulator. Table 2–5 lists the resist- ance checks, and table 2-6 1ists the voltage checks. Table 2–7 is a transistor substitution list. 2-9. Checkout and Repair. a. Voltage Adjustment Rheostat (Rz) (Power Disconnected). (1) Place ohmmeter test probes to terminals of the rheostat (see fig. 2-10). (2) Rotate rheostat fully clockwise, reading should be approximately 250 ohms. (3) Rotate rheostat fully counterclockwise, reading should be less than 5 ohms. (4) If other readings are obtained, replace rheostat. b. Transistors. (1) Remove transistors Q4 and Q5 (see fig. 2–l0). (2) Position transistors as shown in figure 2-1, and check them separately (see fig. 2–2). (3) If resistance values cliffer from the values shown in figure 2–2, replace the transistors through cannibalization or requisition transistor Q4, Vap-Air part number 26316033-12 (2N3441), NSN 5961–00–054–4141, or transistor Q5, Vap- Air P N 26316033–70 (2N3773), NSN 5961–00– 929–5014 (see table 2–7 for substitutes). (4) Check the mica insulating washers be- tween the transistors and mounting plate. Replace if cracked, broken or missing. Coat washers with insulation compound per MIL–S–8660, NSN 6850– 00-880-7616. c. Diode. (1) Remove four screws holding transistor and circiut board mounting plate, and move plate to one side. (2) Place negative ohmmeter probe to the topside of diode D4 (see fig. 2-12). (3) Place positive probe to the bottom of D4. Meter should indicate low resistance. (4) Reverse probes. Meter should indicate high resistance. (5) If other readings are obtained replace diode D4 (MR1122), NSN 5961–00–103–1519 (see fig. 2-12) . d. Relay. (1) Place ohmmeter probes across relay coil terminals (see fig. 2-13). (2) Place ohmmeter probes across terminals (see fig. 2-13). Meter should read infinity (open circuit). (3) If other readings are obtained, replace relay, NSN2920–00–735–9542. (4) Reinstall transistor and circuit board mounting plate. e. Detailed Circuit Checks. (1) Table 2–5 contains “power off’’ resistance checks of the circuit (see fig. 2–15 for test points). (2) Table 2-6 contains “power on” voltage checks of the circuit (see fig. 2–15 for test points). f. Functional Check. Check the performance of the regulator on the test stand and make final volt- age adjustments. Voltage output should read 28 volts. If the regulator does not function properly, perform the following: ( 1 ) Check wires and connections. 2-13