Harris ZX10, Technical Manual

Page: 160 / 198

6-14 888-2595-001 12/20/11
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WARNING: Disconnect primary power prior to servicing.
Section 6 Troubleshooting
ZX Series
Table 6-6 Signal Performance
Symptom Cause and Solution
Poor FM audio
performance (FM
noise, THD, stereo
separation, etc.) Possible fault in exciter. Consult exciter manual for more information on
troubleshooting problem. Amplifier has virtually no impact on transmitted
signal metrics in an FM system.
Switch to reserve exciter (where applicable).
Poor AM noise
performance If problem is synchronous AM noise (appears only with modulation applied),
switch to reserve exciter (where applicable) to determine if problem is
internal to exciter. Consult exciter manual for more information on
troubleshooting problem. Verify original exciter drive cable supplied with
transmitter is still in place. Occasionally, exciter drive cable length has an
impact on synchronous AM noise.
If problem is asynchronous AM (noise remains after all modulation is
removed, including stereo pilot and subcarriers), problem could be in
automatic power control system (APC). Verify power control has been
aligned correctly by consulting procedures in Section 5 - Maintenance. If
problem remains, check +5V test point on controller board (reverse side of
amp front door) with oscilloscope for excessive ripple or other abnormality.
Poor mask compliance
for HD Radio signal Possible input overload of spectrum analyzer. Increase input attenuation to
analyzer to 10dB. If sideband levels drop dramatically (>10dB), problem is
distortion being generated by analyzer overload. Increase input attenuation
until optimal tradeoff between sideband level and noise floor is achieved.
Possible failure of RTAC system. Verify integrity of RF sample from
transmitter output to RTAC input via physical inspection of cables, splitter,
attenuator and via consultation of signal strength bargraph on exciter screen.
Verify XMTR input to RTAC is currently connected at exciter rear panel.
Verify RTAC status is not BYPASS.
Possible power level change since RTAC was last updated. If RTAC is being
kept in HOLD, change to ADAPT and see if compliance improves. When
finished, switch back to HOLD or leave in ADAPT, as desired.
If RTAC has an effect (i.e. is working) but is unable to reach goal, verify
transmitter output power level is correct and meter calibration is not in error.
Check PA AMPS reading (for whole transmitter and individual PA modules)
on front panel meter for excessive current, possibly indicating that
transmitter is being seriously overdriven. Consult procedures in Section 5 –
Maintenance for information checking power meter calibration.
Note: Do not take excessive sideband levels at the exciter output as a sign
that RTAC is not working. In fact, this is generally a sign that RTAC is
working, because the exciter output must be distorted (predistorted) to
compensate for output stage nonlinearities in the amplifier.