In the United States, Canada and other parts of the world, satellite-based transmissions are sent in two kinds of polarities: horizontal and vertical. These two kinds of polarities keep adjacent channels from interfering with one another. On a receiving satellite system there must either be a mechanical antenna that is positioned to receive the desired polarity (channel) or there are two fixed antenna "probes" in each polarity plane and one of them is electronically selected by changing the voltage going to the LNBF.
On most C-Band satellite systems, the polarity is selected mechanically. The part that physically moves the receiving antenna is a small servo motor that is mounted to the feedhorn (the part that points at the face of the dish) and changes the polarity every time that you change channels. This servo motor also has an integrated circuit in it and many other static electricity sensitive components, which make it prone to being damaged by lightning. There are several different versions of servo motors on the market and most have a poor failure rate. This is why we only sell the Astrotel model SM-7 which is fully tested before shipping and has a 1-year warranty.
Changing The Servo Motor
On most satellite systems, this servo motor can be changed in less than 15 minutes. To change this part you will need:
- A small phillips screwdriver that has a shaft length of about 3" or more.
- A flat screwdriver or knife
- Wire cutters
Using the wire cutters, individually cut the three wires connecting the servo motor to the satellite cable near the servo motor.
Remove the four philips machine screws holding the servo motor to the feedhorn.
Using the flat screwdriver or knife, scrape any rubber or silicone that may be on the surface of the feedhorn where the old servo motor was mounted.
Mount the new servo motor to the feedhorn with the original four machine screws that the old servo motor was mounted with.
Connect the three individual wires coming out of the new servo motor to the satellite cable using the Insulation Displacement Connectors that are provided. These unique 3M connectors don't require stripping the insulation off of any of the wires. All you do is insert the two wires (one from the servo motor and one from the satellite cable) into the Insulation Displacement Connector and then take the pliers and squeeze the connector. When you do this, silicone grease will seal the connection helping to reduce corrosion. Continue this procedure with the remaining pairs of wires.
If using a Chaparral (or other brand servo motor that does not have a built-in capacitor), be sure to also connect a 1000 µF (micro-Farad), 5 volt (or greater) capacitor between the +5 V and ground wires at the servo motor as shown in this picture. According to sales manager, Philip Hawkins at R.L. Drake, this capacitor prevents the voltage drop between the receiver and the servo motor. This helps to eliminate the servo motor from "fluttering" after the channel up or down button has been pressed and the servo is supposed to stop moving.
If a picture comes in really quick and then gets snowy again when changing channels on the satellite receiver after the installation of the servo motor, there is a good chance that you will need to manually rotate the black plastic insert in between the actual servo motor and the round plastic piece holding the feedhorn antenna.
To do this, go back out to the dish and remove the four philips screws holding the servo motor to the feedhorn and simply pull off this round plastic piece and rotate it 90°. This piece will be 3/4" wide and have a raised "slot" going diagonally through it. Then reinstall the servo motor. The channels should then come in as they normally did before the old servo motor went out.
If some or all of the channels still don't come in very clear, then you may need to fine tune the "skew" or polarity with your satellite receiver.
If you have additional questions related to servo motors or need to purchase one, please contact us and we will be happy to assist you.