Key  to  fig.  9-1. 1. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 2. Screw Nut Screw Washer Clamp  assy Screw Screw Plate Gasket Screw Cover Gasket Screw Cover Gasket Screw 17. 18. 19. 20. 21. 22. 23. 24. 25. 26. 27. 28. 29. 30. 31. 32. Washer Screen Screw Washer Screw Washer Exciter   assy Screw Clamp Pin Stator Screw Plate Shield Screw Retainer If   any   defective   diodes   are   replaced,   repeat   step   (2) or  (3)  above  to  determine  if  the  generator  defect  has been   corrected. (6)  Tag  and  disconnect  the  two  top  leads  at  pins 15  and  16  of  TB16  (located  on  the  current  transformer mount  plate). Read   the   exciter   field   resistance   at pins  15  and  16  with  a  Wheatstone  bridge.  The  exciter field  resistance  should  be  between  2.90  and  3.55  ohms at   an   ambient   temperature   of   65°F. (7)   Check   insulation   resistance   with   megger   be- tween  pins  15  and  16  and  the  frame  (para  9-2a).  Re- connect   the   two   leads   and   remove   tags.   Before   pro- ceeding   further   with   fault   isolation,   disassemble   the endbell   from   the   generator. (8)   Disconnect   generator   rotor   leads   from   the rotating   diode   assembly   and   measure   the   field   resis- tance  with  a  Wheatstone  bridge.  The  resistance value  for  a  50/60  Hz  generator  should  be  0.38  to 0.46  ohms  and  1.17  to  1.43  ohms  for  a  400  Hz  gen- erator   at   an   ambient   temperature   of   65°F. (9)  Megger  between  field  leads  and  frame  (para 9-2a). (10)  Disconnect  diodes  and  use  a  double  Kelvin bridge  to  read  the  resistance  between  leads  on  the exciter  rotor.  On  a  400  Hz  set,  this  value  is  0.042 to  0.051  ohm  and  on  a  50/60  Hz  set,  this  value  is 0.019  to  0.023  ohm  at  a  65°F  ambient  temperature. (11)   Check   insulation   resistance   with   megger between   exciter   armature   !eads   and   frame   (para   9-2a). (12)   Check   resistance   of   surge   protector   (var- istor)  when  disconnected  from  one  side  of  generator field.  Value  should  be  1  megohm  or  more  in  each direction.   Check   to   be   sure   no   physical   damage   is evident   on   the   surge   protector. (13)   Tag   and   disconnect   the   twelve   stator   leads at  the  voltage  reconnection  panel  and  measure  each of  the  six  stator  windings  with  a  Kelvin  double  bridge. 33. 34. 35. 36. 37. 38. 39. 40. 41. 42. 43. 44. 45. 46. 47. 48. Bearing Cap Screw Washer Washer Cover Gasket Screen Screw Strip Ring Disc Disc Fan Screw Washer 49. 50. 51. 52. 53• 54. 55. 56. 57. 58. 59. 60. 61. 62. 63. 64. 65. Deflector Rotor  assy Hub Key Plate Nut Washer Rectifier    assy Washer Key Rotor Plate Rotor Screw Plate Eyebolt Frame  and stator   assy On  a  50/60  Hz  generator,  the  resistance  should  be 0.0216  to  0.0264  ohm  in  each  circuit.  On  a  400  Hz set,   the   resistance   value   should   be   0.0141   to   0.0173 ohm   in   each   circuit,   at   ambient   temperature   of 65°  F. (14)   Connect   all   stator   leads   together   and   read between  the  leads  and  the  generator  frame  with  a megger   (para   9-2a). (15)  Growler  test (a)  Perform  internal  growler  test  on  stator by  applying  110  Vac  to  the  coil  which  is  wound  on  the cross  bar  of  the  H. (b)  Place  the  growler  on  the  coil  of  the  sta- tor  so  that  it  is  in  direct  contact  with  two  adjacent slots. (c)  A  shorted  coil  produces  a  very  heavy current  which  is  indicated  by  the  rapid  vibration  of a  thin  piece  of  metal,  such  as  a  hacksaw  blade,  held over  the  other  end  of  the  coil. (d)   Perform   a   growler   test   on   the   rotor   as described  in  (a)  above. (e)  Place  the  rotor  on  the  growler  and  ener- g i z e .  (f)  Hold  a  thin  piece  of  metal,  such  as  a hacksaw  made,  directly  over  the  top  slot  of  the  rotor and  along  the  length  of  the  slot.  If  the  coil  is  shorted, the  blade  will  vibrate  rapidly  and  cause  a  growling noise. (16)  If  the  above  test  values  are  not  within  the limits   specified,   proceed   with   the   removal   and   re- pair    procedures. c.   Defective   Bearing   Replacement.   If   a   defective bearing  is  indicated  by  vibration  or  noise  at  the  bear- ing  housing  on  the  endbell,  the  bearing  can  be  re- placed  without  removal  of  the  generator  from  the  set. Change 6 9-3