Specifications
WARNING
ENSURE THAT THE TRANSMITTER IS TURNED OFF AND ALL
PRIMARY POWER IS TURNED OFF AT THE WALL DISCONNECT
SWITCH BEFORE OPENING ANY DOOR OR PANEL. BEFORE
REMOVING PANELS OR OPENING DOORS, VERIFY THAT THE
RF AMP POWER SUPPLY IS DISCHARGED BY CHECKING
“PA+VDC” ON THE FRONT PANEL MULTIMETER. USE A VOLT-
METER TO VERIFY THE POWER SUPPLIES HAVE BEEN DIS-
CHARGED PRIOR TO TOUCHING ANY COMPONENTS.
a. Start by ensuring that the RF modules are firmly inserted
in the Combiner Motherboard.
b. If the fault remains follow the steps below.
1. Using a clip lead, jumper the cathode of CR30 to R120
(J4-19 to J4-9).
2. If DS2 goes out, refer to the Overall wiring diagram and
the Combiner Motherboard section to trace an open
cable.
3. If DS2 is still illuminated, check the voltage on U36-2
for a logic low.
4. If U36-2 is a logic low, check the voltage on TP18 and
compare this to the voltage on U36-5.
5. If TP18 is higher than U36-5, check CR35, R49, R120,
C90 and CR32.
6. If TP18 is lower than U36-5, replace U36.
7. If U36-2 is a logic high, replace U3.
8. If no indicator (DS2-DS5) is illuminated then check the
cathode of CR34 for a logic low.
9. If CR34 is a logic high refer to the Transmitter Interface
and Controller Sections to continue.
10. If CR34 is a logic low check U35-9 for a logic high.
11. If U35-9 is high replace U48.
12. If U35-9 is low, suspect U35 or CR35.
L.4.3.3 Fuse Fault
L.4.3.3.1 DS6 illuminated
a. If DS6 is illuminated and no RF AMPS indicate blown
fuses(DS1orDS2)checkTP32foralogiclow.
b. If TP32 is a logic high, suspect U48,C110, and U35.
c. If TP32 is a logic low determine which stage is producing
the fault by checking for a logic low on the cathodes of
CR24, CR26, CR28 and CR30.
NOTE
Since the circuitry is the same for all fuse faults only one (CR24
low) will be used as an example. Refer to the Mod Encoder sche-
matics to find the correct component for the actual stage produc-
ing the fault.
1. If the cathode of CR24 is low, compare the voltages on
U34 pins 10 and 11.
2. If U34-11 is lower than pin 10, suspect R53 or CR22.
3. If these components are okay it may be possible that the
modules being protected by that circuit are not being
turned on or a fuse on one of the fuse boards is blown.
4. Refer to the transmitter Troubleshooting section on
Control front panel indicators and the Overall wiring
Diagram to Continue.
5. If U34-11 is higher than pin 10 replace U34.
L.4.3.3.2 None are Illuminated
If none of the LEDs are illuminated on any of the Mod Encoders
check the cathodes of CR33 and CR34 for a logic low. The diode
with the logic low is on the board generating the fault. Check
U35, CR35 and CR34 on that Encoder board.
L.4.3.3.3 Air Flow and Temperature Sensing
There are three types of sensing circuits on this board that are
summed together to generate air flow or temperature faults.
a. The Air Flow sensor in the cabinet
b. The on Board air Flow sensing for the B+ heatsink, and
c. The temperature sensor mounted on RF1.
If the Control front panel display shows an Air Flow Reduced,
Air Flow fault, Temp and/or a Foldback fault and the Transmitter
troubleshooting section has referred to the Modulation Encoder,
begin troubleshooting by observing if DS7 is illuminated on the
Mod Encoder board.
NOTE
The Fault must be active at the time of troubleshooting. This can
be determined by the fact that Fault Reset on the Control front
panel does not clear the fault.
If DS7 is illuminated:
a. Check TP7 and TP6 for a voltage greater than 3VDC.
b. If TP7 is greater than 3V then the temperature sensing
circuit for RFA1 is faulty.
c. If TP6 is greater than 2.5VDC then an air flow sensing
circuit has failed.
L.4.3.3.4 RF1 Temperature Sensing
a. If TP6 measures greater than 3VDC, the ambient air tem-
perature is less than 50 Degrees C., and air flow to the
modules is not restricted, then:
b. Check the circuitry by removing power and carefully
bending U6-6 out of the socket.
c. Turn on the transmitter.
d. If the fault remains, replace U6.
e. If the fault clears replace the temperature sensor on the RF
Amp Module.
L.4.3.3.5 Air Flow Sensor
If TP7 is greater than 3 VDC, the ambient air temperature is less
than 50 degrees C, and air flow is not restricted to the compart-
ment or over the Modulation Encoder board heatsink,then:
a. Check U38-2 for approximately +5VDC.
b. If not present suspect an open cable from the external air
flow sensor.
c. If the voltage is present on U38-2, check U38 pins 2 and
3.
d. If pin 2 is greater than pin 3 replace U38 or U41, or check
external air flow sensor, if used.
e. If pin 2 is less than pin 3 suspect a faulty U44.
888-2339-002 L-11
WARNING: Disconnect primary power prior to servicing.