TM  1-1520-240-10            4-1-5 4-1-3). Check OFP and EID numbers are correct for the- ater or mission. Performs  the  Receiver  and  AN/AVR-2  status  display. See figure 4-1-4 for normal indicator displays, and faulty indicator displays. Performs a test on the synthetic voice status messages. A no fault detected during test will end with message APR-39 OPERATIONAL” any fault detected will end with message “APR-39 FAILURE”, which will be heard over the ICS. Performs the plus (+) symbol display status. The plus (+) symbol will be displayed, centered within the small circle on the indicator, anytime the symbol is operational. Figure  4-1-3.  Radar Signal Detecting Set (OFP and EID VERSION DISPLAY) (c) MODE switch — MODE 2 (down), (d) TEST switch — Press. Performs the synthetic voice short count. Listen to syn- thetic voice message and adjust volume. Mode 2 short count is: “SELF-TEST SET VOLUME 5, 4, 3, 2, 1”. (2) The following fault display conditions are on the result of a bad self test and will result in an audio message “APR-39 FAILURE” over the ICS. (a) If a receiver fault is noted, faulty receiver is shown as two triangles, (fig. 4-1-4) representing right and left video channel (s) will be flashing. (b) A faulty C/D band amplifier in a proces- sor is shown as a flashing square centered on indicator display ( fig. 4-1-4). (c) The   Laser   Detecting   Set   (LDS)(AN/ AVR-2) status is displayed along with the receiver status. A faulty LDS quadrant is shown as a flashing asterisk. LDS  faults  do  not  cause  an  audio  message  “APR-39 FAILURE”, heard over the ICS. (d) If LDS is not installed, all four quadrants (asterisks) will flash. (3) Operating In A Dense Signal Environment. (a) When a dense signal environment is de- tected, the plus (+) symbol on the Radar Signal Detecting Set (RSDS) indicator will flash, and the voice message “THREAT DETECTION DEGRADED” will be announced over the ICS. (b) Position mode switch to mode 2 (terse mode).  When  the  plus(+)  symbol  stops  flashing,  the voice  message  “THREAT  DETECTION  RESTORED” will be announced over the ICS. 4-1-5.  Countermeasure Set (AN/ALQ-156). The  Countermeasures  Set  (AN/ALQ-156)  detects  the approach of anti-aircraft missiles, and signals the M-130 Flare Dispenser to launch flares to decoy the missiles from the helicopter. The set consists of a control unit on the  console,  a  receiver-transmitter  in  the  electronics compartment, two antennas on the bottom of the fuse- lage, and two caution light capsules on the master cau- tion panel. The set alternately applies pulsed signals to the  two  antennas  which  radiate  the  signals  about  the helicopter.  A  missile  approach  is  detected  by  the  fre- quency  shift  of  the  transmitted  signals  echo  returned from the missile. Any echo is received during the interval following each pulsed transmission. Built-in-test-equip- ment monitors system operation. If a malfunction is de- tected, the system is disabled and the CM INOP caution capsule on the master caution panel will come on. Also, if  enemy  jamming  or  interference  from  other  counter- measures sets is detected, the set will automatically shift to a clear channel. The set receives AC electrical power from the No. 2 AC bus through the MSL DET SYS circuit breaker on the No. 2 PDP. The set receives DC power from the No. 2 DC bus through the MSL DET SYS circuit breaker also on the No. 2 PDP.