Specifications

Start troubleshooting by checking to see which Power Supply
Indicator DS5 or DS6 is illuminated.
E.7.2.4 Power Supply A Overtemp
If Power Supply Overtemp A indicator is illuminated, proceed
as follows,
a. Measure the voltage on TP11. Multiply this reading by 10
to obtain a temperature reading in degrees Centigrade.
b. If this appears high or abnormal compared to the suspected
actual temperature of the rectifier heatsinks, the sensor or
U3 may be faulty.
1. The voltage on TP11 should be 10 times greater than
the voltage on the input amplifier.
2. If the voltage is at the proper level, replace the sensor.
3. If not, replace the amplifier and or associated circuitry.
If the reading for TP11 seems normal, repeat the above
procedure at TP12.
c. If TP11 and TP12 appear normal, compared to the sus-
pected rectifier heatsinks, troubleshoot the fault compara-
tors. The outputs should be a logic low during a fault
condition.
1. Check to see if the voltage at the (+) input is more
positive than the (-) input.
2. If it is, replace the comparator.
E.7.2.5 No Indicator Illuminated
a. If no indicator is lit and the transmitter is on with foldback
active,check U2 and the transistor Q7 for properoperation.
E.7.2.6 Power Supply B Overtemp
If Power Supply Overtemp B indicator is illuminated, use the
same procedure as above using the corresponding test points.
E.7.2.7 Buffer Fault Sensing
If a Buffer Fault indicator is illuminated on the Control front
panel and the transmitter may be turned on with an RF MUTE
applied, start troubleshooting as follows.
a. If the Buffer Fault output is logic low at J3, measure the
reference voltages when Predriver A is selected.
1. U15-4 should be +2.5VDC and TP1 should be
+4.3VDC.
2. If not present, check for a defective CR1 or CR2.
b. Check for the Buffer sample.
1. Measure TP1 and TP2 for a voltage greater than the
previously measured reference voltage.
2. If the sample is not greater than the reference, check for
a failed U1, an open cable, or a fault on the Driver
Combiner Motherboard. Refer to the overall wiring
diagram and the Driver Combiner Section as needed.
3. If the sample is greater than the reference, replace the
comparator.
c. If the Buffer Fault output at J3 is a logic high, refer to the
overall wiring diagram, Transmitter Interface, and the
Controller schematics to determine the cause of the logic
low.
E.7.2.8 Predriver Fault Sensing
If a Predriver Fault indicator is illuminated on the Control front
panel and the transmitter may be turned on with an RF MUTE
applied, start troubleshooting as follows:
a. Check the Predriver Fault output at J3 for a logic low.
b. If low, check the reference voltage on the (-) input of the
comparator, should be 2VDC.
1. If the voltage is less than 2VDC, remove the comparator
and re-check.
c. Check the Predriver sample.
1. If the voltage on TP3 is less than the reference, check
for a failed U1, an open cable, or a fault on the Driver
Combiner Motherboard. Refer to the overall wiring
diagram and the Driver Combiner Section as needed.
2. If the sample is greater than the reference, replace the
comparator.
d. If the Predriver Fault output at J3 is logic high, refer to the
overall wiring diagram, Transmitter Interface, and the
Controller schematics to determine the cause of the logic
low.
E.7.3
Driver Control
There are two types of driver control present on the Driver
Encoder Board:
a. Predriver Select
b. Driver Turn On
Refer to the corresponding section below for problem being
addressed.
E.7.3.1 Predriver Select
If the Predriver cannot be switched on when S1 is toggled, begin
troubleshooting as follows:
a. Check for +15VDC on the collector of Q3 when S1 is in
the Predriver A position.
1. If missing, check J8-9 on this board for +15VDC.
2. If J8-9 has +15VDC refer to the overall wiring diagram
and Driver Combiner Motherboard schematic to trace
where the +15VDC is being lost. J8-9 supplies
+15VDC to the Predriver Select relays on the Driver
Combiner Motherboard, while J8-7 is the return line
back to the Driver Encoder.
b. If Q3 has +15VDC present, then switch to the Predriver B
position and check to see that the collector has gone logic
low.
1. If not, the switch could be defective or R51 could be
open.
c. If the above circuits and components check good, the
Predriver Select relay on the Driver Combiner may have
failed. Refer to the Driver Combiner Troubleshooting Sec-
tion to continue.
E.7.3.2 Predriver and Drivers D1 - D6 Will Not Turn On
a. If the Predriver is not being turned on, check the D0 output
of the PAL for a logic high, when JP9 is in the TEST
position.
E-8 888-2339-002
WARNING: Disconnect primary power prior to servicing.