Specifications

Linear Audio / Video / Data Solutions
Reference Section 73
No Picture
Verify that the video source is on and is producing a video signal.
Check that the TV and the modulator are tuned to the same
channel. For example, if the modulator is broadcasting on UHF
channel 16, make sure the TV is on UHF 16 rather than CATV 16.
UHF 16 and CATV 16 are at different frequencies.
Weak Modulated UHF Channel
If the TV has a separate UHF input, be sure that it is connected.
LEDs on the Modulator Blink
The display will blink if you have assigned the same channel to
multiple inputs. You need to have one unused channel space
between channels.
Diagonal Lines, Known as Herringbone Interference,
on Modulated Channels
You may have chosen a channel number that is not completely
vacant. Distant UHF stations may be unviewable, but will cause
interference if you try to create a new channel at the same
frequency. Also, cable companies often have extra signals where
there should be none. Move the modulated channel to another
number. You may have to add a low-pass filter to remove cable
company noise. If a filter does not work, try adding a DC-block to
remove common mode interference.
Herringbone Interference on Multiple Channels,
Including Modulated Channels
If the problem disappears when you remove the CATV/Ant feed
then the RF amplifier is overloaded by abnormally strong signals.
Often, you can cure the problem with a simple attenuator. Use
a variable attenuator and try to find a signal level where the
interference just disappears. Sometimes, the problem is one
station that is far stronger than the rest. Attenuating all of the
signals with a simple attenuator will cause the desired stations to
be weak (snowy). In this case you must reduce the strength of only
the offending station. A common FM trap will help if the problem is
a nearby FM tower. If the problem is a nearby TV station, often the
station management can provide suitable filters.
Audio Volume is Low
The left and right audio inputs are combined for monaural. For
proper audio level, both right and left inputs must be used. If you
have a mono source, connect it to both right and left inputs using
an RCA ‘‘Y’’ connector.
No Color on Modulated Channels
You may have chosen the incorrect cable standard. Not all
televisions can accommodate the 1.25 MHz frequency difference
between the H and I cable standards.
Trouble with the Infrared Remote Control
Use the red IR DATA light on the modulator as a troubleshooting
aid. This light will blink as remote control signals are relayed. If the
light is constantly on, one or more of the IR targets is receiving
electrical or optical noise. At the distribution unit, begin to
disconnect the outputs to the TVs until the IR DATA light goes off.
This will tell you which IR target is the source of the noise. Next,
cover the front of the offending IR target. If the IR DATA light turns
off, the IR target is “seeing” a source of IR noise, such as a solid-
state fluorescent lamp. If the light does not go out, the problem
may be radiated electrical noise from the plasma or direct-view TV.
Reposition this IR target. On 5-volt systems, if repositioning the IR
target does not help, the TV may be conducting noise from its
input. Place a DC block between the IR target and the TV. If
the IR DATA light seems to indicate a proper operation, but
the component is not being controlled, the IR emitter may be
mislocated. Be sure the emitters are in front of the IR sensor on
the video source.
Troubleshooting with
Channel Plus
linearcorp.com / 1 800 421 1587