5-2
TROUBLESHOOTING Orban Model 8400
Problems and Potential Solutions
Always verify that the problem is not the source material being fed to the 8400, or in
other parts of the system.
Headphones Don’t Work
The headphone jack is connected to chassis ground, and won’t work if the 8400’s chassis
ground is not connected to its circuit ground. If the headphones don’t work, switch the
rear-panel
Ground Lift switch to Ground.
RFI, Hum, Clicks, or Buzzes
A grounding problem is likely. Review the information on grounding on page 2-11. The
8400 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.
Particularly if you are using a long run of coaxial cable between the 8400 and the exciter,
a ground loop may inject noise into the exciter’s composite input—especially if the ex-
citer’s input is unbalanced. The Orban CIT25 Composite Isolation Transformer can al-
most always cure this problem.
The AES/EBU 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. See step
13 on page 2-29.
Poor Peak Modulation Control
The 8400 ordinarily controls peak modulation to an accuracy of ±2%. This accuracy will
be destroyed if the signal path following the 8400 has poor transient response. Almost
any link can cause problems. Even the FM exciter can have insufficient flatness of re-
sponse and phase linearity (particularly at low frequencies) to disturb peak levels. Section
1 of this manual contains a complete discussion of the various things that can go wrong.
Digital STLs using lossy compression algorithms (including MPEG1 Layer 2, MPEG1
Layer 3, and Dolby AC2, and APT-X) will overshoot severely (up to 3 dB) on some pro-
To Next Page
Loading...
