TM 55-1510-222-10 should   be   manually   synchronized   before   turning   the synchrophaser on. NOTE If  the  synchrophaser  is  ON  but  does not adjust properly, the synchrophaser  has  reached  the  limits of  its  range.    Turn  the  system  OFF, manually adjust the propeller RPM into synchronization, then turn the synchrophaser ON. The   propeller   synchrophaser   may   be   used   on takeoff  at  the  pilot's  option.    If  used  for  takeoff,  the limited range of the synchrophaser will be reduced near maximum propeller RPM. b.  Control Box.  The control box, located forward of   the   pedestal,   converts   pulse   rate   differences   into correction commands.  Differences in pulse rate, and/or propeller  position,  causes  the  control  box  to  vary  the voltage   in   the   primary   governor   coil,   which   in   turn increases  propeller  speed  until  the  correct  speed  and phasing  is  obtained.    The  system  is  protected  by  a  5- ampere circuit breaker placarded PROP SYNC, located in the overhead circuit breaker panel (fig. 2-6). c.    Synchroscope.    The  propeller  synchroscope indicator,     located     in     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, 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 the propellers. 2-48.  PROPELLER LEVERS. Two  propeller  levers  on  the  control  pedestal  (fig. 2-11),  placarded  PROP,  are  used  to  regulate  propeller speeds.  Each lever controls a primary governor, which acts   to   regulate   propeller   speeds   within   the   normal operational   range.      The   full   forward   position   of   the levers is placarded TAKEOFF, LANDING AND REVERSE   HIGH   RPM.      The   full   aft   position   of   the levers is placarded FEATHER.  When a lever is placed at HIGH RPM, the propeller may attain a static RPM of 1700 depending upon power lever position.  As a lever is  moved  aft,  passing  through  the  propeller  governing range,    but    stopping    at    the    feathering    detent,    the propeller   RPM   will   correspondingly   decrease   to   the lowest   limit   (approximately   1390   RPM).      Moving   a propeller  lever  aft  past  the  detent  into  FEATHER  will feather the propeller. 2-49.  PROPELLER REVERSING. CAUTION Do  not  move  the  power  levers  below the flight idle gate unless the engine is running.  Damage to    the    reverse linkage mechanisms will occur. Propeller     reversing     on     unimproved     surfaces should  be  accomplished  carefully  to  prevent  propeller erosion from reversed airflow.  Consideration should be given to reversing propellers when operating in snow or dusty   conditions,   to   prevent   obscuring   the   operator's vision. The    engine    power    levers    actuate    an    engine mounted cambox which is connected to the engine FCU (fuel control unit) and the propeller reversing cable.  The cambox  is  arranged  so  that  the  reversing  cable  is  not affected  by  power  lever  movement  forward  of  the  idle stop.      When   the   power   levers   are   lifted   over   the reversing   detent   and   moved   rearward,   the   reversing cable  is  pulled  aft.    This  action  resets  the  Beta  valve rearward,  allowing  the  governor  to  pump  more  oil  into the    propeller,    thus    moving    the    blades    through    the ground  fine  range  towards  reverse  pitch.  As  the  blades move,    the    mechanical    feedback    collar,    is    moved forward.    This  movement  is  transmitted  by  a  carbon block   on   the   end   of   the   reversing   lever   to   the   Beta valve, causing it to move forward.  When the Beta valve reaches  its  initial  position,  oil  flow  to  the  propeller  is blocked preventing further blade angle change.  As the power   levers   are   moved   further   rearward   (into   the striped  area),  the  propeller  blades  are  moved  further toward  the  reverse  pitch  stop,  and  the  FCU  is  reset  to increase engine speed. 2-50.  PROPELLER TACHOMETERS. The   two   tachometers   on   the   instrument   panel register propeller speed in hundreds of RPM (fig. 2-14). Each indicator is slaved to a tachometer generator unit attached to the corresponding engine. Section VII.  UTILITY SYSTEMS 2-51.  DEFROSTING SYSTEM. a. Description.        The    defrosting    system    is    an integral part of the heating and ventilation system.  The system consists of two warm air outlets connected by 2-45