TM  55-1510-221-10 the  switches  reads  PROP  GOV  TEST.  Each  switch controls  test  circuits  for  the  corresponding  propeller. In  the  test  position,  the  switches  are  used  to  test  the function   of   the   corresponding   overspeed   governor. Refer  to  Chapter  8,  for  test  procedure.  Propeller  test circuits  are  protected  by  one  5-ampere  circuit breaker  placarded  PROP  GOV  located  on  the  over- head  circuit  breaker  panel  (fig.  2-26). 2-46.   PROPELLER   SYNCHROPHASER. a. Operation.  The  propeller  synchrophaser automatically  matches  the  RPM  of  the  right  propel- ler (slave propeller) to that of the left propeller (mas- ter  propeller)  and  maintains  the  blades  of  one  pro- peller  at  a  predetermined  relative  position  with  the blades  of  the  other  propeller.  To  prevent  the  right propeller  from  losing  excessive  RPM  if  the  left  pro- peller  is  feathered  while  the  synchrophaser  is  on,  the synchrophaser   has   a   limited   range   of   control   from the  manual  governor  setting.  Normal  governor  oper- ation  is  unchanged  but  the  synchrophaser  will  con- tinuously  monitor  propeller  RPM  and  reset  the  gov- ernor  as  required.  A  magnetic  pickup  mounted  in each   propeller   overspeed   governor   and   adjacent   to each   propeller   deice   brush   block   transmits   electric pulses  to  a  transistorized  control  box  installed  for- ward  of  the  pedestal.  The  right  propeller  RPM  and phase   will   automatically   be   adjusted   to   correspond to   the   left.   To   change   RPM,   adjust   both   propeller controls  at  the  same  time.  This  will  keep  the  right governor  setting  within  the  limiting  range  of  the  left propeller.  If  the  synchrophaser  is  on  but  is  unable  to adjust  to  the  right  propeller  to  match  the  left,  the actuator   has   reached   the   end   of   its   travel.   To recenter,  turn  the  switch  off,  synchronize  the  propel- lers  manually,  and  turn  the  switch  back  on. b. Control  Box.  The  control  box  converts  any pulse   rate   differences   into   correction   commands, which  are  transmitted  to  a  stepping  type  actuator motor  mounted  on  the  right  engine  cowl  forward support  ring.  The  motor  then  trims  the  right  propel- ler   governor   through   a   flexible   shaft   and   trimmer assembly  to  exactly  match  the  left  propeller.  The trimmer,  installed  between  the  governor  control  arm and  the  control  cable,  screws  in  or  out  to  adjust  the governor  while  leaving  the  control  lever  setting  cons- tant.  A  toggle  switch  installed  adjacent  to  the  syn- chrophaser  turns  the  system  on.  With  the  switch  off, the  actuator  automatically  runs  to  the  center  of  its range  of  travel  before  stopping  to  assure  normal function   when   used   again.   To   operate   the   system, synchronize  the  propeller  in  the  normal  manner  and turn  the  synchrophaser  on.  The  system  is  designed for  in-flight  operations  and  is  placarded  to  be  off  for take-off  and  landing.  Therefore,  with  the  system  on and   the   landing   gear   extended,   the   master   caution lights  will  illuminate  and  a  yellow  light  on  the  cau- tion/advisory   annunciator   panel,   PROP   SYNC   ON, will   illuminate. c.  Synchroscope.  The   propeller   synchroscope, provides   an   indication   of   synchronization   of   the propellers.   If   the   right   propeller   is   operating   at   a higher  RPM  than  the  left,  the  face  of  the  synchro- scope,  a  black  and  white  cross  pattern,  spins  in  a clockwise   rotation.   Left,   or   counterclockwise,   rota- tion   indicates   a   higher   RPM   of   the   left   propeller. This  instrument  aids  the  pilot  in  obtaining  complete synchronization  of  propellers.  The  system  is  pro- tected   by   a   5-ampere   circuit   breaker   placarded PROP  SYNC,  located  on  the  overhead  circuit breaker  panel  (fig.  2-26). 2-47.   PROPELLER   LEVERS. Two  propeller  levers  on  the  control  pedestal  (fig. 2-7),  placarded  PROP,  are  used  to  regulate  propeller speeds.   Each   lever   controls   a   primary   governor, which   acts   to   regulate   propeller   speeds   within   the normal  operation  range.  The  full  forward  position  of the  levers  is  placarded  TAKEOFF,  LANDING  AND REVERSE  -  and  also  HIGH  RPM.  The  full  aft  posi- tion  of  the  levers  is  placarded  FEATHER.  When  a lever   is   placed   at   HIGH   RPM,   the   propeller   may attain  a  static  RPM  of  2,000  depending  upon  power lever   position.   As   a   lever   is   moved   aft,   passing through  the  propeller  governing  range,  but  stopping at   the   feathering   detent,   propeller   RPM   will   corre- spondingly   decrease   to   the   lowest   limit.   Moving   a propeller   lever   aft   past   the   detent   into   FEATHER will  feather  the  propeller. 2-48.  PROPELLER  REVERSING. Do  not  move  the  power  levers  into reverse  range  without  the  engine  running. Damage   to   the   reverse   linkage   mecha- nisms  will  occur. Propeller   reversing   on   unimproved   sur- faces  should  be  accomplished  carefully  to prevent  propeller  erosion  from  reversed airflow   and,   in   dusty   conditions,   to   pre- vent  obscuring  the  operator’s  vision. 2-40