TO: ALL AIRWAY FACILITIES DIVISION MANAGERS

ATTN: AIRWAY FACILITIES SECTOR MANAGERS

SUBJ: (MODE S) LOSS OF BEACON VIDEO WHEN POWER CYCLING STANDBY

INTERROGATOR FOR MODE S IN INDEPENDENT BEACON INTERROGATOR

(IBI)

TWX: TWX-MODES-4002

DATE: 8/9/94

ON THE STANDBY MODE S BEACON INTERROGATOR, WHEN THE MAIN POWER IS

CYCLED BETWEEN OFF TO ON, LOSS OF BEACON VIDEO FROM THE ONLINE

INTERROGATOR WAS REPORTED FROM SEVERAL MODE S (IBI) FACILITIES. THIS

WAS CAUSED BY FOLLOWING THE PROCEDURES IN MEASURING THE RECEIVER AND

STC SENSITIVITY ACCORDING TO PARAGRAPH 156 IN THE MODE SELECT (MODE S)

BEACON SYSTEM MAINTENANCE HANDBOOK (6360.XX). THIS PROBLEM ALSO

OCCURED WHILE PERFORMING ANY CORRECTIVE MAINTENANCE ACTION WHICH

INVOLVES CYCLING OFF/ON POWER TO THE STANDBY BEACON INTERROGATOR.

THE CAUSE IS A POWER ON GLITCH FROM CERTAIN VSWR MONITOR BOARDS (A116

IC CHIP U25) IN THE INTERROGATOR, CAUSING THE VIDEO TRIGGER DRIVER

BOARD IN THE MODE S JUNCTION BOX (MSJB) TO SELECT THE WRONG CHANNEL'S

OUTPUT VIDEO.

UNTIL FINAL RESOLUTION OF THIS PROBLEM, IT IS SUGGESTED THAT SCHEDULED

DOWN TIME BE REQUESTED FROM ALL FACILITIES TO ASCERTAIN IF THIS PROBLEM

EXISTS IN EITHER CHANNEL. THIS CAN BE ACCOMPLISHED BY FIRST REQUESTING

DOWN TIME, POWERING OFF/ON THE STANDBY INTERROGATOR, AND OBSERVING LOSS

OF BEACON TARGETS ON THE RTADS DISPLAY.

THIS PROBLEM MAY HAVE BEEN PREVIOUSLY CHECKED BY VISUAL INSPECTION OF

THE MANUFACTURER TYPE OF THE CHIP ON THE A116 BOARD AT THE U25

POSITION. HOWEVER, FURTHER INSTANCES PROVE THAT THE ABOVE TEST MUST

BE PERFORMED TO ENSURE OPERATIONAL INTEGRITY OF THE SYSTEM.

FURTHER, IF THE CONDITION DOES EXIST AT YOUR FACILITY, IT IS

RECOMMENDED THAT SCHEDULED DOWN TIME BE REQUESTED WHEN PERFORMING ANY

FUTURE MAINTENANCE WHICH REQUIRES POWER OFF/ON CYCLING OF THE STANDBY

MODE S INTERROGATOR UNTIL THE BOARD IS REPLACED, AND ANOTHER ONE

ORDERED WITH THE PROPER CHIP (TEXAS INSTRUMENTS) INSTALLED.

IF YOU HAVE ANY FURTHER QUESTIONS REGARDING THIS MESSAGE, PLEASE

CONTACT DANIEL TRONGONE, AOS-510 (609) 485-HELP.

EDWARD SCHUMAN

MANAGER, NATIONAL DATA COMMUNICATIONS

SYSTEMS ENGINEERING DIVISION, AOS-500