Broadcast Electronics FM-5T, User Manual, Page: 152 / 191

1-5
1-21.
INTERLOCKS.
1-22. The internal interlock circuitry consists of a series string of normally closed switches
mounted in areas which contain electrical or mechanical hazards. Each switch is mechani
cally activated by a door or panel to deenergize the entire transmitter when opened. If an
internal interlock opens, the transmitter will deenergize immediately. The transmitter
must be manually restored to operation after the open interlock is closed. The controller
front-panel INTERLOCK indicator will extinguish to indicate an open interlock. If the
opened internal interlock is closed before the filament cool-down timer interval expires,
the blower will re-energize for the remaining duration of the cool-down cycle and then de-
energize. If the air pressure interlock opens, the power supplies will de-energize immedi
ately. When the interlock closes, the transmitter will return to operation automatically.
1-23. The failsafe interlock circuitry consists of an external switch such as from a test load or
remote control failsafe circuit connected to the failsafe interlock terminals on the remote
interface circuit board. If the failsafe interlock is opened, only the high voltage plate sup
ply will be deenergized. The controller FAILSAFE and HIGH VOLTAGE indicators will
extinguish to indicate an open interlock. When the failsafe interlock is closed, the trans
mitter will return to operation automatically.
1-24.
OVERLOAD OPERATION.
1-25. Plate current, screen current, control grid bias supply current, and PA reflected power are
monitored for overload conditions. If an overload occurs, the overload initiate an overload
control sequence.
1-26. Any overload will illuminate the OVERLOAD indicator and initiate two timed intervals.
A timer and counter monitors the number of times an overload occurs during a 60 second
interval. A second overload recycle timer delays restoration of the transmitter to operation
to allow the condition that prompted the overload to dissipate.
1-27. When the timed interval delaying restoration of the transmitter to operation has expired,
the transmitter will recycle back into operation. If no further overloads occur during the
60 second interval following the first overload, the 60 second timer will clear the overload
counter. If four overload recycles occur during the 60 second counter/timer interval, the
transmitter will deenergize and must be manually reset. This can be done by depressing
the OVERLOAD switch/indicator, the FILAMENT ON switch/indicator, and the HIGH
VOLTAGE ON switch/indicator. The overload can also be cleared by remote control if re
mote control is enabled.
1-28. If an overload persists in duration for longer than 0.22 seconds, the controller will consider
the overload a short circuit and immediately deenergize the transmitter. The transmitter
must then be manually restored to operation after the fault is repaired.
1-29. The overload reset sequence is initiated when the OVERLOAD RESET switch/indicator
is depressed. When the switch/indicator is depressed, the following actions will occur.
1. The OVERLOAD RESET switch/indicator and the overload diagnostic indicator
( PLATE, SCREEN, GRID, or VSWR ) indicator will extinguish.
2. The overload timer/counter will be reset.
3. The overload recycle timer will be reset.
1-30.
EMI I/O CIRCUIT BOARD.
1-31. All controller inputs and outputs are routed through connectors J1, J2, and J3 mounted to
the EMI I/O circuit board. The circuitry consists of PI-section low-pass LC filters effective
to 108 MHz and connected in series with each input and output to prevent RF leakage into
the controller. Each input/output also contains a transzorb. The transzorb limits the in
put/output signal to
±
15 volts.