TM  5-6115-323-14 Section X. MAINTENANCE OF THE CONTROL BOX ASSEMBLY 4-24. General The generator sets, both the AC and DC units, are  each  equipped  with  a  control  box  mounted over  the  generator.  They  provide  a  housing  for the components required to control the electrical functions  of  the  generator  and  they  provide  a mounting  point  for  the  operator’s  controls  and instruments and the power output terminals. The control  boxes  are  similar  in  general  appearance and  function.  However,  several  of  the  components, within, differ between the two units. Also, the AC unit  control  box  contains  several  more  compo- nents  than  is  contained  in  the  DC  units.  The components within the two control boxes that are the responsibility of organizational maintenance are covered separately, for the AC and DC units, by  paragraphs  in  this  section. 4-25. Control Box Components (AC Unit) a. Test. Test the AC control box components as follows: (1) Voltmeter. (a) Remove  load  cables  from  load  terminals. (b) Start the generator set. (c) Position  load  switch  to  ON  position. (d) With a multimeter, measure the output voltage across the load terminals to verify voltage on  the  set  voltmeter.  Voltage  should  not  vary more than 5%. (e) If voltage variation exceeds 5%, replace the voltmeter. (2)  Voltage  Changeover  Switch. (a) With the power off, disconnect the volt- age changeover switch. (b)  Position  switch  on  120  V  setting  and check continuity between the center terminal and the 120 V terminal. (c)  Position  switch  on  240  V  setting  and check continuity between the center terminal and the 240 V terminal. (d) If  a  malfunctioning  open  circuit  is  indi- cated  on  either  position,  replace  the  switch. (3) Load  Switch. (a) Stop  generator  set  and  disconnect  termi- nals  to  load  switch. (b) With a multimeter, check the continuity of the load switch. OFF position will indicate an open  circuit;  ON  position  will  indicate  a  short circuit. (c) If the above readings are not obtained, replace  the  load  switch. b. Removal. Refer to figure 4-17 and remove the control  box  components. c. Cleaning  and  Inspection. (1) Clean all parts thoroughly. (2)  Inspect   the   variable   resistor   knob   for cracks  and  stripped  thread. (3) Inspect the voltmeter and frequency me- ter for signs of burning, broken or cracked glass, water  damage,  and  other  damage. (4) Inspect the terminal boards for cracks and burned  areas. (5)  Inspect  the  load  and  voltage  changeover toggle   switches   for   proper   operation,   signs   of burning,  loose  wire  contacts,  stripped  threads,  and other  damage. (6) Inspect the receptacle connector for loose connections,  signs  of  burning  and  other  damage. (7) Replace all defective parts. d. Installation.  Refer to figure 4-17 and install the control box components. 4-26. Control Box Components (DC Unit) a. Test. Test the DC control box components as follows: (1) Voltmeter. (a) Remove  load  cables  from  load  terminals. (b) Start  the  generator  set. (c) Position  the  circuit  breaker  to  the  ON position. (d) With a multimeter, measure the output voltage across load terminals to verify the voltage on  the  set  voltmeter.  Voltage  should  not  vary more than 4 volts. (e) If voltage variation exceeds 4 volts, then replace  the  voltmeter. (2) Load Meter., (a) Connect  a  load  of  known  wattage  and proper voltage output terminals of the generator set. Maximum load is 1500 watts. (b)  Start  the  generator  and  place  circuit breaker  in  ON  position.  Observe  the  reading  on the set load meter. Meter should indicate accord- ing to the load attached, i.e., 375 watts-25%; 750 watts-50%,   etc. (c)  If  the  load  meter  does  not  read  within specifications,  replace  it. 4-22 Change  1