Specifications

When the incoming eight bit digital word from U16 matches the
programmed eight bit digital word, U4-19 goes low.
The anode of CR2 is grounded and a voltage divider applies
+3VDCtothebaseofQ1.
This saturates the transistor and the collector is pulled high. This
high signal is applied to Encoder Positioning Jumpers P5 and P6,
and will turn ON the Programmable RF Amp.
When the incoming eight bit digital word from U16 is greater
than the programmed eight bit digital word, U4-19 goes high and
U4-1 goes low. The Programmable RF Amp is still turned ON.
For more information on setting the Programmable RF Amp see
the Emergency Bypass procedures in Section 6A.
L.4.2.7 Data Strobe
A Data Strobe signal from the A/D Board enters at J8-25 and
drives the Clock inputs of the Latches.
Each Latch is clocked by a low-to-high transition, so the Data
Strobe-L pulse must be inverted.
Inverter U15-2 provides the low-to-high transition at the begin-
ning of the Data Strobe-L pulse. This results in the eight bit
digital word present at the inputs of the Latches being transferred
to the outputs at the same constant level until the next DataStrobe
signal occurs.
L.4.2.8 RF Mute
The RF Mute line is tied to the Clear input on all Latches.
When the RF mute line is low all latch outputs go low, turning
OFF all Big Step RF Amplifiers. Inverter U15-6 goes high and
DS1 RF Mute is illuminated YELLOW.
An RF Mute signal is generated when any of the following occur:
a. The transmitter is turned off and in the Test Mode.
b. A Manual RF Mute is activated on the Controller board.
c. A Remote Control RF Mute is activated via the External
Interface board.
d. A Cable Interlock-L fault exists on any of the 5 Mod
Encoder Boards.
e. The Output Monitor board detects excessive VSWR.
f. The A/D Converter detects a conversion error.
L.4.2.9 RF Amplifier Test
The RF Amp Test allows testing of the Encoder Output Drivers,
connecting cables, and the RF Amp turn-on/turn-off control
circuits by presenting a high on the input to the Encoder Output
Drivers.
The circuit consists of a P10 1-4 which is connected to +5VA
through limiting resistor R85.
L.4.2.10 Module/Cable Interlock
Refer to Figure L-3 Cable Interlock and Fuse Fault Detection
Circuits for the following discussion.
The Cable Interlock circuit will turn the transmitter OFF if any
of the interconnecting cables between the Modulation Encoder
Boards and Combiner Motherboards are disconnected, or any RF
Amplifiers are not installed. If any circuit generates a fault, the
Encoder Cable Interlock LED will illuminate RED in addition
to any on board indicator. A Cable Interlock Fault will not allow
the transmitter to be turned ON until the fault is cleared.
There are 4 interlock circuits on each Mod Encoder, each inter-
lock circuit monitors 8 RF Amplifier modules.
Since all interlock and associated control circuits are the same,
only one interlock will be discussed.
The cable interlock function is provided by two series connec-
tions. When all the RF Amps and Mod Encoder cables are
properly connected, a closed circuit is established from J1-9 to
J1-10 (by four RF Amps and one cable) and from J1-20 to J1-19
(by four RF Amps and one cable).
Due to the voltage divider action of R89, R91, R53(7,8),
R52(6,1), and R53(5,6) and R52(4,1), the voltage at the + input
of comparator U34-9 will be greater than the voltageat the - input
U34-8.
When the interlock connection between J2-20 and J2-9 is opened
by removing the encoder cable or unplugging an RF Amplifier,
the voltage at the + input will be lower than the voltage at the -
input due to the additional voltage drop provided by CR22.
The output of U34-14 would go low and diode CR25 will
conduct and establish approximately 0.6VDC at the input of
U48-1.
Inverter U3-2 will go high and the Interlock 1 indicator DS5 will
be illuminated RED.
Whenever U48-1 is pulled low by CR25, CR27, CR29, CR31,
or CR4, Inverter U48-12 goes high and saturates transistor Q2.
An RF MUTE-L is applied to turn ALL Big Step and Binary RF
Amplifiers OFF.
Inverter U48-10 goes high and saturates the transistor inside
U35- 8. J7-7 goes low and the Controller will shut the transmitter
OFF.
L.4.2.10.1 Interconnection Cable Interlock
When J8 is connected, J8-31 receives +5VDC from the Trans-
mitter Interface. If this cable is disconnected, inverters U48-
2/U48-4 and diode CR4 will pull U48-1 Cable Interlock low.
Due to the diode gating, none of the Interlock indicators will be
illuminated RED.
L.4.2.11 Fuse Fault Detectors
Refer to Figure L-3 Cable Interlock and Fuse Fault Detection
Circuits for the following discussion.
The open fuse detector circuits will cause the RF Amp Fuse LED
to illuminate RED when one or more of the 160 Big Step or
Binary RF Amplifiers has an open Supply Voltage or RF Drive
fuse.
Other than the visual indication, no other action is taken by the
transmitter.
L.4.2.11.1 Supply Voltage Open Fuse Detection
There are 4 detector circuits on each Mod Encoder, each detector
monitors 8 RF Amplifier modules. Since all detector and associ-
ated control circuits are the same, only one detector will be
discussed.
L-6 888-2339-002
WARNING: Disconnect primary power prior to servicing.