TM 1-1510-218-10 2-71 propeller  is  feathered  while  the  synchrophaser  is  on, the synchrophaser has a limited range of control from the    manual    governor    setting.         Normal    governor operation   is   unchanged   but   the   synchrophaser   will continuously   monitor   propeller   RPM   and   reset   the governor 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 forward 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   propellers   manually,   and   turn   the switch back on. (1)   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 propeller 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 constant.    A  toggle  switch  installed  adjacent  to  the synchroscope  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  caution  flashers and a yellow light on the caution/advisory annunciator panel, PROP SYNC ON, will illuminate. b.  Description   T   .         The   propeller   synchro- phaser    automatically    matches    the    RPM    of    both propellers,    and    maintains    a    preset    phase    angle relationship  between  the  left  and  right  engine.    Input signal    pulses,    occurring    once    per    revolution,    are obtained  from  magnetic  pickups  (located  on  brackets bolted   to   the   front   of   the   engine)   when   the   target (mounted   on   the   aft   side   of   the   spinner  bulkhead) passes  the  magnetic  pickup.    A  control  box  converts this     signal     pulse     rate     difference     into     correction commands,  which  are  transmitted  to  the  appropriate governor.   Speed trim is accomplished by pulse width modulation     of     an     electromagnetic     coil     in     each governor.   The electromagnetic coil can increase, but not  decrease,  the  speed  set  by  the  propeller  control level.   The RPM of one engine will follow the changes in   RPM   of   the   other   engine   over   a   predetermined range   (approximately   20-RPM).       A   toggle   switch, placarded  PROP  SYN  ON  /  OFF,  installed  near  the synchroscope,  turns  the  system  on.    To  operate  the system,    synchronize    the    propellers    in    the    normal manner  and  turn  the  synchrophaser   ON.    To change RPM,  adjust  both  propellers  at  the  same  time.    This will  keep  the  setting  within  the  limited  range  of  the system.  The propeller synchrophaser may be used on takeoff   at   the   pilot's   option.      However,  the  limited range   of   the   synchrophaser   will   be   reduced   near maximum propeller RPM. 2-55.  SYNCHROSCOPE. A  propeller  synchroscope,  located  on  the  pilot's instrument panel, 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  synchroscope,  a  black  and  white  cross  pattern, spins in a clockwise rotation. Left, or counterclockwise,  rotation  indicates  a  higher  RPM  of the  left  propeller.    This  instrument  aids  the  pilot  in obtaining complete synchronization of propellers.  The system   is   protected   by   a  5 -ampere  circuit  breaker, placarded   PROP   SYNC,   located   on   the   overhead circuit breaker panel. 2-56.  PROPELLER LEVERS. Two   propeller   levers   on   the   control   pedestal, Figures  2-7  and  2-9, 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 levers     forward     position     is     placarded     TAKEOFF, LANDING AND REVERSE and also HIGH RPM.  Full levers  aft  position  is  placarded   FEATHER.    When  a lever is placed at HIGH RPM, the propeller may attain a  static  RPM  of  2000,  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  correspondingly decrease to the lowest limit.  Movi ng a propeller lever aft   past   the   detent   into   FEATHER   will   feather   the propeller. 2-57.  PROPELLER REVERSING. CAUTION Do not move the power levers into reverse range without the engine running.  Damage to    the    reverse    linkage    mechanism    will occur.