(b)
Pull the three generator control circuit breakers C4, C5 and C6 on the load control center right (P6-4). See wiring diagram manual 24-21-11, -21 or -31 depending on generator number.
(c)
Measure generator exciter field resistance. The field resistance measured from F to A terminals should be at least 8 ohms.
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(3)
Rotating rectifier has failed.
(a)
Determine if generator rotates [Ref 4.C.(1)(a)].
(b)
Determine that exciter field is not open or shorted [Ref step 4.C.(2)].
(c)
Check voltage regulator by exchanging the generator control unit (GCU) for one that is known to function properly. Also check connections at voltage regulator terminals on the GCU for continuity and short circuits.
(d)
If test equipment is available, check generator rotating rectifier (Ref 24-21-61).
(4)
Shorted feeder lines.
(a)
Remove generator feeder lines from generator terminals T1, T2 and T3.
(b)
Check for open, or infinity on ohmmeter, between feeder lines, phase to phase, and phase to neutral. If continuity exists, the feeder lines are shorted.
D. Constant Speed Drive
(1) Input shaft has failed, generator shaft has sheared, disconnect has failed.
(a)
With engine running, check residual voltage at generator terminals, and check that constant speed drive is not disconnected [Ref 4.C.(1)].
(b)
If drive is connected and the residual voltage is zero, the input shaft or the disconnect unit has failed. If the low pressure light on the overhead panel is off and still no residual voltage, the generator shaft is sheared.
(c)
If disconnect does not actuate properly, check circuit; if circuit checks, replace transmission. 1) Disconnect connector D6 from CSD wiring harness. 2) Measure resistance of CSD disconnect solenoid coil between pins 3 and 4 of
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wiring harness. Check that resistance is less than 100 ohms. 3) Check continuity to ground of pins 3 and 4 of connector D6. 4) Set meter to measure dc voltage and monitor voltage of pin 6 on D6. 5) Place BAT switch on P5 panel to ON. Set CSD DISCONNECT switch to ON. 6) Verify voltage on meter is approximately 28 volts while switch is held to ON and
zero when switch is released. 7) Remove meter, restore airplane to normal, and lockwire switch.
(d) If disconnect does not reset properly, replace transmission.
(2)
Disconnect unit has failed.
(a) Ref 4.D.(1)(c) and (d).
(3)
Drive has failed internally.
(a) Remove and inspect magnetic drain plug. The presence of reasonably large pieces of bright metal on the magnetic plug indicates a drive failure.
NOTE: A small amount of fine or fuzzy granular material is normal.
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BTB GCB GCR VOLT-METER FREQ METER ANNUNCI -ATOR SIGNAL AC AM-METER READING CIRCUITS* LOCKED OUT CSD LOW PRESSURE LIGHT CSD TEMP
Closed Open Open Zero Zero FF Zero Off Safe
Closed Trip Trip Zero Zero FF_LV* Zero Off Safe
Trip Trip Closed Zero Zero LV Zero LV Off Safe
Closed Trip Trip Above 129 400 HV -- Off Safe
Closed Trip Trip 115 400 FF -- Off Safe
Open One Trip Trip Zero LV Zero Off Safe
Closed Open Closed Zero Zero No Signal Zero On Safe
Closed Open Closed 115 400 No Signal Zero Off Safe
Closed Trip Trip -- -- LV Zero LV Off Safe
Closed Trip Trip Below 97 -- LV -- LV Off Safe
Closed Open Closed 115 400 No Signal Zero Off Safe
Open Trip Closed 115 400 LV Zero UF Off Safe
Open Closed Trip Zero Zero LV Zero LV Off Safe
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