Specifications

Modulated B- Drive from the Analog Input board feeds a Bal-
anced To Unbalanced Amplifier that drives the B- Regulator and
the B- Fault Tracking circuit.
The output B- voltage from the B- Regulator varies with modu-
lation and passes through Output Protection and is applied to the
Normal Mode jumper.
Since the B- signal is constantly changing, the B- Fault Tracking
circuit provides a reference for the Output Fault Sense.
L.4.1.3 Normal And Bypass Mode
When the Modulation Encoder is operated in the Normal mode,
B+ and B- is distributed to all Encoder Output Drivers. If the
jumper is moved to the Bypass mode, B+ is supplied to all
Encoder Output Drivers and all RF Amplifiers are turned OFF.
L.4.1.4 Module/Cable Interlock And Fuse Fault Detectors
L.4.1.4.1 Module/Cable Interlock Detector
The Module/Cable Interlock Detector circuits on each Modula-
tion Encoder board will generate a Module/Cable Interlock fault
that will turn the transmitter OFF whenever an RF Amplifier is
not inserted or an Encoder Output cable is disconnected. The
Module/Cable interlock line from all 5 Mod Encoders, as well
as from the Driver Encoder, are combined in a six input AND
gate on the Transmitter Interface, and a single fault line is then
sent to the Controller.
L.4.1.4.2 Fuse Fault Detector
The Fuse Fault Detector circuits on each Modulation Encoder
board will indicate an RF or +230VDC fuse(s) has opened on an
RF Amplifier. This will illuminate the RF AMP FUSE indicator
RED on the Control front panel.
L.4.1.5 Air Flow/Temperature Sensing
The Function Selector on the A25, A26, and A28 Modulation
Encoders is jumpered for Air Flow monitoring. An onboard Air
Flow Sensor and up to 2 additional Air Flow Sensor Inputs are
combined and sent to the Air Flow Detector.
If air flow is reduced up to a certain level, the Air Flow Detector
will generate an Air Flow Fault-TX Foldback that will cause the
Controller to foldback power output until a safe operating level
is reached.
If a further reduction in air flow occurs, the Air Flow Detector
will generate an Air Flow Fault-TX OFF, which will turn OFF
the transmitter.
The Function Selector on the A29 Modulation Encoder is jum-
pered for temperature sensing. An external thermal monitor U1
Figure L-2. Simplified Encoder Output Drivers
888-2339-002 L-3
WARNING: Disconnect primary power prior to servicing.