Figure 3-4. Figure 3-5. TM 55-4920-402-13&P (2) (3) (4) (5) (6) (7) (8) (9) (10) (11) Set  up  Tester  rotor  for  double  interrupter (all  six  interrupter  screws  installed). Set Strobex MODE switch to A. Illuminate  Tester  rotor  with  Strobex.  Verify that  the  stem  of  the  h  in  the  logo  appears stopped  at  12:00,  3:00,  6:00,  and  9:00 o’clock (fig. 3-5). Set   Tester   CAM   RATE   (RPM)   and Balancer  RPM  TUNE  to  1800.  RPM RANGE  to  X10.  Observe  the  same results. Set  INTERRUPTER  LOGIC  switch  to SINGLE. Shut  off  Tester. Remove  the  two  opposite  pairs  of  interrupter screws  on  the  Tester  (four  total)  leaving  only the two opposite single screws (fig. 3-3). Run  the  Tester  at  1800  RPM  and  illuminate the  rotor  with  the  Strobex.  Verify  that  the stem  of  the  h  appears  stopped  at  12:00 and  6:00  o’clock. Set  Tester  CAM  RATE  (RPM)  and Balancer  RPM  TUNE  to  900.  RPM RANGE  to  Xl.  Observe  the  same results. Shut  off  Tester. c. Performance Check of the Strobex Locking Oscillator  Mode. (1)   Remove   interrupter   screws   from   the   Tester disc  leaving  only  the  one  to  which  the  stem of  the  h  points  (fig.  3-6). 3-6 Change  4 (2) (3) (4) (5) (6) (7) (8) (9) (10) (11) Set Strobex MODE switch[  to position E and RPM dial to 090. Run Tester at 1800 RPM and illuminate Tester rotor with the Strobex. Adjust Strobex RPM dial until the stem of the  h  appears  stopped  at  6:00  o’clock. Set Strobex RPM dial to 180 ( actual rotor  rate)  and  adjust  Strobex  RPM  dial  until the  stem  of  the  h  appears  stopped  at  12:00 and  6:00  o’clock. Reduce the Strobex, RPM dial setting while observing the h image. Verify that the stem of  the  h  remains  at  6:00  o’clock  but  the 12:00 o’clock stem moves clockwise until about 2:00 or 2:30 o’clock. Further deduc- tion of the Strobex RPM dial setting causes, the image to become very erratic. Set Strobex MODE switch to B and RPM dial to 180 (450 rotor RPM times one blade times 0.4, as stated on Strobex rear panel). Operate Tester at 900 RPM and illuminate Tester disc with the Strobex. Adjust Strobex RPM  dial  until  sterr  of  h  appears  stopped at 6:00 o’clock. Increase the Strobex RPM dial setting to slight- ly above 180 and verify that the image starts revolving  counterclockwise. Set Strobex RPM dial to 360 and adjust until the  stem  of  the  h  appears  stopped  at  12:00 and 6:00 o’clock. Reduce the Strobex RPM dial setting while observing  the  h  image.  Verify  that  the  stem of  the  h  remains  at  6:00  o’clock  and  the 12:00  o’clock  stem  moves  clockwise.