TM 55-4920-402-13&P or the Strobex clock angle image. When properly tuned, no phase shift will be seen; i.e. no clock angle change will be seen when the VERIFY TUNE button is pushed or released. Typical phase relationships for improperly and properly tuned filters are shown in figure 2-5. c. Further, there should be little or no change in IPS whether the VERIFY TUNE button is pushed or released. This should always be checked, but the actual tuning should be accomplished by adjusting for no change in clock angle. d. Because of the lower circuit time constants, the VERIFY TUNE button must be pressed and released for longer intervals when working at-low rotor RPM (4 or 5 seconds) for main rotors. Conversely, it may be worked more rapidly when doing tail rotors. NOTE Adjust  RPM  TUNE  only  while  VERIFY TUNE button is pushed. The brief tun- ing instructions on the Balance Charts are carefully worded. Follow them exactly and you will find it an easy and effec- tive  process. 2-5. Use of the Balancer. The Phazor section of the Bal- ancer is a phase meter with a display in the form of a ring of 24 lights. It is used with the Balancer to read the loca- tion of imbalance of main rotors. The ringof-lights indi- cate clock angle which, along with the IPS meter reading, determines the point to be plotted on the chart. a. The Phazor section derives its inputs (Magnetic Pickup pulse, and filtered Accelerometer signal), from the Balancer. The user observes which of the 24 lamps is lit and reads the hour or half-hour as from a clock face. This indication is used when working main rotors, for estab- lishing a clock angle on the Balance Chart. The IPS is read from the Balancer meter. b. The Strobex is used as the phase meter when mea- suring clock angle of tail rotors. NOTE When using the Strobex to determine the clock angle of the tail rotor, the Phazor lights are not used. c. The only Phazor controls is a TEST pushbutton to verify that it is receiving the correct Magnetic Pickup pul- scs for phase reference, and a DOUBLE/SINGLE INTER- RUPTER LOGIC switch to set the correct interrupter logic. d. The Phazor requires a one-per-revolution pulse from the Magnetic Pickup on the fixed swashplate as a phase reference to measure the clock angle of the Accelerometer signal. However, most helicopters are fitted with one Interrupter per blade so as to trigger the Strobex for track- ing. This causes the Magnetic Pickup to deliver two pulses per revolution which is not suitable for the Phazor. Since there is only one Magnetic Pickup on the fixed swashplate, both the tracking and balancing requirements must be met by arranging the logic of the pulses. This is the reason for fitting the rotating swashplate with one double and one single interrupter. e. Once-per-revolution, the Strobex sees triggering pul- ses, one of which is double. Time constants in the Strobex are such that it cannot see the difference between the double and single pulses, so it flashes once per blade, and the two Tip Targets are displayed at each of the two posi- tions in azimuth around the rotor disc. f. The Phazor, however, has logic that looks only at the double pulse and ignores the single pulse. Thus, it thinks it  is  receiving  only  the  one-per-revolution  reference  signal it requires. When the TEST button on the Phazor is pushed, the Accelerometer input is disconnected and only the Magnetic Pickup pulse train is admitted. The double pulse causes the 12:00 o’clock lamp to light, and the single pulse will light the 6:00 o’clock lamp. In summary, with the TEST button pushed, the 12:00 o’clock and 6:00 o’clock lights will be seen. g. The display described in paragraph f must appear in the Phazor with the TEST button pushed, or the VIBREX is not ready for use. h. To realize the above logic, the INTERRUPTER LOGIC  switch  must  be  in  the  DOUBLE  position. i. After application of the Magnetic Pickup pulses to the Phazor, several seconds are required for the circuit to stabilize. Failure to stabilize after 10 to 20 seconds could be caused by improper gap between the Magnetic Pickup and Interrupters. j. When the TEST button is released, only one lamp will be lit, and that one is in response to the Accelerometer signal, so it may be anywhere on the clock. 2-6. Use of the Strobex.  The Strobex has a trigger in the pistol-grip handle for dc power switching, a five-position function switch, and a ten-turn RPM dial to adjust the flash rate. Figure 2-4 illustrates the relationship of the Strobex to airframe mounted components. Observe steps a through c when using the Strobex. NOTE Focus   on   the   flash   focue   tube   in   its parabolic     reflector   is   essential. Therefore,  periodically  shine  the  light on   a   wall   10   to   20   feet   distant   and check  for  a  bright  spot  1  to  2  feet  in diameter.  Refer  to  paragraph  3)10C  for focus    adjustment. a. Be sure the lamp is correctly focused. b. Be sure to use clean reflective targets. c. Be sure to look directly over top of lamp (the reflec- ted light comes back to the light source). 2 - 6 Change  3