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.