Section 5: Troubleshooting; Problems And Potential Solutions - Orban OPTIMOD 5750 Operating Manual

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Orban 5750 Technical Manual Troubleshooting

Section 5: Troubleshooting

Problems and Potential Solutions

Always verify that the problem is not the source material being fed to the 5750, or in other parts of the system.
RFI, Hum, Clicks, or Buzzes
A grounding problem is likely. Review the information on grounding on page 2-1. The 5750 has been designed with
very substantial RFI suppression on its analog and digital input and output ports, and on the AC line input. It will
usually operate adjacent to high-powered transmitters without difficulty. In the most unusual circumstances, it may
be necessary to reposition the unit to reduce RF interference, and/or to reposition its input and output cables to
reduce RF pickup on their shields.
It is not recommended to use a long run of coaxial cable between the 5750 and the exciter as a ground loop may
inject noise into the exciter's composite input—especially if the exciter's input is unbalanced.
The AES3 inputs and output are transformer-coupled and have very good resistance to RFI. If you have RFI problems
and are using analog connections on either the input or output, using digital connections will almost certainly
eliminate the RFI.
Unexpectedly Quiet On-Air Levels
The ITU412 multiplex power controller may have been turned on accidentally.
The 5750 may be in stand-alone stereo encoder mode. The active on-air preset determines this.
The 5750 may not be controlling peak modulation as desired. See the next topic below.
Poor Peak Modulation Control
First, if you are using the analog or digital output to drive the transmitter, make sure that this output is not receiving
the MONITOR.
The 5750 normally controls peak modulation to an accuracy of ±2%. This accuracy will be destroyed if the signal path
following the 5750 has poor transient response. Almost any link can cause problems. Even the FM exciter can have
insufficient flatness of response and phase-linearity (particularly at low frequencies) to disturb peak levels.
Digital STLs using lossy compression algorithms (including MPEG1 Layer 2, MPEG1 Layer 3, Dolby AC2, and APT-X)
will overshoot severely (up to 3 dB) on some program material. The amount of overshoot will depend on data rate
— the higher the rate, the lower the overshoot.