TM 5-6115-590-12 (c) Adjust   potentiometer   until   voltage begins  to  increase  on  panel  400  Hz  AC  voltmeter,  and increase voltage to 120V AC line-to-neutral. NOTE If load contactor trip Indicator Illuminates due to under-voltage, reset load contactor switch and increase voltage to 120V AC (d) If  120  volts  are  obtainable  and  the load contactor does not trip, the 400 Hz generator output is  correct  and  the  voltage  regulator  has  failed.    If  120 volts  are  not  obtainable,  the  generator  or  other  400  Hz components are defective.  Refer to paragraph 4-62 for 400 Hz generator maintenance instructions. (4) Installation.      Install   voltage   regulator   in reverse order of removal. f. Relay assemblies K2,K3,K4 and K5 through K9 (fig.  4-37). (1) Removal. (a) Tag  and  disconnect  wiring  harness connector plug on relay assembly. (b) Remove   six   (6)   attaching   screws and  washer  and  remove  relay  assemblies  from  upper electrical power chassis. (2) Cleaning and Inspection. (a) Clean   relay   assembly   with   filtered compressed air or wipe with a clean rag moistened with an  approved  cleaning  solvent.    Clean  receptacle  with filtered compressed air or an electrician's brush. (b) Visually  inspect  relay  assembly  for corrosion, cracks, damaged threads or other evidence of damage. (3) Test. (a) Remove   connector   P3   from   relay assembly  (K2,K3,K4)  and  connect  a  source  of  24V  DC across pins S and H on relay assembly connector J3. (b) Check for continuity between pin M and N, pin A and L, and pin P and R. (c) Move the 24V DC source connection  at  pin  S  to  pin  G  so  that  the  24V  DC  is connected across pins G and H of connector J3. (d) Check that there is continuity between   the   four   pins   A,   B,   C   and   D.      Check   for continuity    between    pins    P,    K    and    R.        Check    for continuity between pin E and pin F, pin S and pin J, and pin V and pin W. (e) Disconnect the 24V DC source from connector  J3.    If  continuity  is  not  present  between  the pins specified in steps (b) and (d), the relay assembly is defective. (f) Remove   connector   P4   from   relay assembly  K5  through  K9  and  connect  the  positive  side of a source of 24V DC to pin E and the negative side to pin  F  on  the  relay  assembly  connector  J4.  Check  that there is continuity across the following pins on connector J4: K and L, H and J, M and Q, G and D. (g) Without     removing     the     24V     DC connections from pins E and F, jumper the positive side of  the  source  so  that  it  is  connected  to  both  pin  E  and pin W (pin F is a common negative for both relay coils). The  circuit  between  pins  M  and  Q  should  now  check open. (h) Remove   the   positive   jumper   from pin  W  and  connect  it  to  pin  e  so  that  the  positive  24V DC   is   not   connected   to   pins   E   and   e.      Jumper   the negative side of the voltage source to pin f, so that the negative  24V  DC  is  connected  to  both  pin  F  and  pin  f. The circuit between pin G and pin d and between pin Y and pin Z should check open.  The circuit between pins b and c should show continuity. (i) Remove     the     jumpers     from     the connector and connect the 24V DC source across pins t and F.  Check for continuity between pins a and s, and between pins n and p.  There should be continuity. (j) Move the 24V DC source connections to place the 24V DC across pins W and X. Check   for   continuity   between   pins   R   and   S,   and   for continuity between three (3) pins T, U and V. (k) Remove the 24V DC source. Check for continuity between pins Y and Z, C and B, g and  h,  and  between  the  three  pins  A,  0  and  N.    If  the circuit between pins does not check as outlined in steps (f) through (k), the relay assembly is defective. (4) Installation.        Install    replacement    relay assembly in reverse order of removal. g. Protective Panel (two used, 60 Hz and 400 Hz). (1) Removal.        Tag    and    disconnect    wiring harness connector plug from protective panel figure4-37.        Remove    six    (6)    attaching    screws    and washers and remove protective panel. (2) Cleaning and Inspection. (a) Clean    protective    panel    assembly with  filtered  compressed  air  or  wipe  with  a  clean  rag moistened  with  an  approved  cleaning  solvent.    Clean receptacle with filtered compressed air or an electrician's brush. (b) Visually inspect panel for corrosion, cracks, damaged threads or other evidence of damage. (3) Test.  If either the 400 Hz main contactor trip   indicator   lamp   or   the   60   Hz   load   contactor   trip indicator lamp illuminates and 60 Hz or 400 Hz power is lost, reset the 400 Hz main contactor switch or the 60 Hz load  contactor  switch,  as  applicable.    If  the  system  trip indicator  lamp  again  illuminates  and  power  is  lost,  the protective panel for the applicable system has failed. NOTE If  upon  resetting  either  the  60  Hz  load contactor   or   the   400   Hz   main   contact switch,   the   system   ammeter   pegs   full scale, check for a short circuit or overload condition in the system. 4-88