3
6
2
3.3
TROUBLESHOOTING:
If the visual and/or aural output signals from the transmitter appear distorted, noisy or nonexistent,
consider the following procedure as a troubleshooting aid. This procedure assumes the transmitter
wiring as well as the cabling and connectors are trouble free. It also assumes the modulator is
receiving baseband video and audio signals while providing the required visual and aural IF
carriers at appropriate levels of
8dBm peak and
21dBm average, respectively. The general
problem area will be indicated by simply checking the front panel diagnostic lights as well as the
transmitter and Exciter RF POWER meters. The diagnostic indicators are located on the front
panel of the EMEX1 Exciter and on the Control/Metering panel at the top front of the transmitter
cabinet.
3.3a
Control/Metering Panel Indicators:
1.
Under normal operation the following indicators will be lit green:
AMPLIFIER
POWER SUPPLY
RF POWER meter = 100% with FWD green/<10% with REFL green
2.
In standby operation the AMPLIFIER indicator will be lit green.
3.
If the POWER SUPPLY indicator fails to illuminate with the transmitter in OPERATE, it is
signaling that one of the 32V power supplies in the 500W Power Amplifier drawer indicated
(A3PS1 or PS2 / see Figure 3
6
1) has failed and needs to be replaced. Until that time, the
IF/Converter’s output AGC circuit is deactivated allowing the transmitter to operate at
reduced power.
4.
If the AMPLIFIER light goes out with the transmitter providing power, it indicates that one
of the output transistors in the 500W Power Amplifier drawer has failed. If a qualified
technician is available, the defective transistor can be replaced; otherwise, replace the
affected 300W Power Amplifier assembly (A3A1, A3A2) or 500W Power Amplifier drawer
(A3). In the interim, the fault indication has deactivated the IF/Converter’s output AGC
control so that the transmitter can operate at lower power.
5.
If the AMPLIFIER TEMP indicator lights yellow, this is a sign that one of the 300W Amplifier
Assemblies in the 500W Amplifier drawer is operating at a temperature high enough to
cause transistor damage. This fault usually occurs due to high ambient temperature at the
transmission site, amplifier drawer cooling fan failure or lack of maintenance allowing for
fouled fans and blocked front panel air vents.
6.
Assuming that the transmitter had previously been operating at its appropriate power and
none of the indicators discussed above are showing a fault, if the FWD RF POWER meter
is now reading less than 100% with the Exciter RF POWER meter indicating 100% (AGC
off) or more (AGC on), a loss of gain has occurred somewhere in the system after the
Exciter’s output. Check first for faulty cables or a detuned/defective output UHF Bandpass
Filter (A7FL1). Next, check the gain of the 500W Power Amplifier drawer. Neither the
Splitter (A3CP1), Combiner (A3CP2) nor driver amplifier transistors contained in the 500W
Power Amplifier are monitored and, if faulty, will cause loss of gain. Identify the problem
component and replace the affected drawer, amplifier assembly, module or component as
soon as possible. If it is necessary to operate the transmitter before repairs are effected,
be sure to defeat the output AGC by releasing (out) the Exciter’s AGC/MANUAL button.