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3-4 TM 55-4920-400-13 Section   IV. ELECTRICAL   SYSTEM 3-8.  Capacitor  Replacement.  Remove   electro- lytic filter capacitor from chassis for replacement as follows: a.  Removal. (1) Remove chassis assembly from tester case (para. 2-46). (2) Unsolder wiring harness leads from termi- nals on capacitor. (3) Remove nuts, terminal, and screws secu- ring bracket and ground leads to chassis. (4) Remove capacitor and bracket assembly. b.    Installation. (1) Place capacitor and bracket assembly in position on chassis, insert screws, install ground leads and terminal, and secure with nuts. (2) Solder leads to terminals on capacitor. (3)  Install  chassis  assembly  in  tester  case (para. 2-46). 3-9. Transformer.  The  stepdown  transformer  is inspected, replaced, and tested as follows: a.  Inspection. (1) Inspect transformer for signs of excessive heat such as melted solder or wax, burned insu- lation, and odor of burned materials. (2) Check terminal to see that connections are tight. (3) Check leads for shorted or bare wires. b.  Removal.  If  it  is  necessary  to  replace  the transformer, proceed as follows: (1) Remove chassis assembly from tester case (para. 2-46). (2) Unsolder wiring harness leads from termi- nals on transformer. (3) Remove nuts, lockwashers and screws se- curing transformer to chassis, and remove trans- former. c.  Installation. (1) Place transformer in position on chassis and secure with screws, lockwashers, and nuts, (2) Solder wiring harness leads to terminals on transformer. (3)  Install  chassis  assembly  in  tester  case (para. 2-46). d. Test. (1) Insert a variac or an equivalent variable transformer  in  the  primary  circuit  of  the  trans- former and set the input at 115 volts. (2)  Provide  a  test  setup  having  a  load  suf- ficient to cause a 2,2 ampere flow of current in the secondary circuit. (3)  Check  the  voltage  across  the  secondary output. It should be approximately 26 volts. 3-10.   Motor   and   Pump   Assembly,   Remove, clean, and inspect motor and pump assembly as di- rected in paragraph  2-54; disassemble, as required to perform the procedures which follow: a. Inspection.  At  disassembly,  inspect  motor and pump assembly as follows: (1)  Check  resistance.  between  motor  input leads and ground. Reading should be approximately 1,7 ohms. (2)   Check   field   windings   for   continuity, grounds, and shorts. {3) Examine bearings for excessive wear and other defects. (4) Inspect commutator for signs of high mica at commutator segments. b. Repair.  Replace any defective motor or pump parts, such as a grounded or shorted field winding assembly,   worn   bearings,   defective   armature or pump shaft. Repair a commutator which has high mica by undercutting as follows: (1) Using an approved method carefully un- dercut the mica between the commutator segments to a depth of 0.005 to 0.010 x 3/64 of an inch. Be sure the full width of the mica is removed and that a thin (2)  Remove  all  burrs  and  rough  edges  from slots by beveling gently to a 45° chamfer. (3) Polish with a very fine grade of sandpaper and finish with felt or canvas. c.  Lubrication.  Prior  to  reassembly  of  motor and pump, lubricate motor shaft bearings using bearing   grease,   Military   Specification   MIL-G- 23827,  as  instructed  on  the  current  lubrication order (Refer to fig. 3-2). d. Test.  Prior to installing the motor and pump assembly in the chassis, it can be tested as follows: (1) Arrange the unit in a test setup comprised of a reservoir, pressure gauge, relief valve (55 psig), vacuum tank, vacuum gauge, and necessary piping. (2) Apply 28 vdc power to the motor. In re- peated tests the pressure gauge should rise consis- tently to approximately 50 psig. Stop the motor at this  point. (3) Check the vacuum gauge; it should read approximately   -29.5   Hg.    e.  Reassembly  and  Installation.  For  reas- sembly and installation procedures, refer to para- graph 2-54.

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