Diodes

Figure 4-2. Fuel Transfer Pump Relay K20, Test Setup

TM-5-6115-593-34 Generator Set Diesel Engine Driven Tactical Skid Mtd. 600 Kw 3 Phase 4 Wire 120/208 and 240/416 Volts Manual
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TM5-6115-593-34 NAVFAC P-8-631-34 TO-35C2-3-463-2 possible AC-DC short. (4) Carefully inspect the wiring to make certain the AC wires are not touching the DC wires. If no wires are touching, the primary and secondary of transformer T1 or reactor T2 may be shorted. Disconnect the secondary of transformer T1 from the diodes CR1 and CR2. Measure with ohmmeter from INPUT terminal to one of the transformer T1 secondary leads. If there is an ohm-meter indication, there is an insulation breakdown between primary and secondary windings. The transformer should be replaced. (5) Check both INPUT terminals to ground (chassis), and check both OUTPUT terminals to ground. If the meter indicates full-scale deflection, a wire is touching ground. b. Diodes. (1) Test silicon diodes (CR1 and CR2) as follows: (a) Disconnect one end of the diode. (b) Connect an ohmmeter (scale set Rx100) across the diode, note the reading. Now reverse ohmmeter leads to the diode, and again note reading. A good diode will read high resistance one way and low resistance the other way. A shorted diode will read full scale both ways. An open diode will read infinity (no reading) in either direction. Check all diodes and replace disconnected leads. (2) Test zener diode (CR4) as follows (see figure 4-3): (a) Connect a 20-40V DC variable power source to the battery charger. (b) Connect a voltmeter across the zener diode (CR4) and resistor R1. (c) Voltmeter must read only 22 volts while input voltage is varied from 20 to 30 volts DC. c. Cutout Relay. Test the cutout relay (54, figure 4-4) as follows. See detail in figure 4-3. (1) Connect a 120V AC source with a SPST switch (S1) as shown. (2) With S1 closed, using an ohmmeter, check for continuity between contacts 3 and 6. (3) Open switch and disconnect 120V AC. d. Transistor Control Circuit. (See figures 4-3 and 4-4.) (1) With power disconnect from battery charger, remove fuse F3. Connect a DC ammeter (0 to 50 amps) across fuse holder. (2) Connect 120V AC input power to battery charger and record ammeter reading. Remove input power. (3) Remove two wires from T2 (46, figure 4-4) and Q1 (68) connected to terminal 1 of TB1 (65). (4) Temporarily connect these two wires together using a jumper. (5) Connect 120V AC input power to battery charger. (6) Record ammeter reading. If the reading is higher than reading recorded in step (2), the transistor control circuit may be defective. Check CR4 (69), (paragraph b(2), above) and check for open resistor R1 (74). If CR4 and R1 are not defective, replace transistor Q1 (68). (7) Remove ammeter from fuse 4-5

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