How to Solve Dish Moving Issues in Actuators and Dish Movers

Most c band dish antennas are moved by using an actuator to do the physical moving, and a dish mover to supply power to the actuator. Dish movers are sold under many names with the most common being sold under the names Vbox or Gbox. The actuator is nothing more than a glorified screw that is attached to a motor. The motor is connected to a set of gears which could be referred to as a transmission.

There is also a reed switch in most actuators that tell the dish mover the exact position of the screw which is located inside the actuator housing or actuator tube. Many different positions may be stored in the dish mover which allows us to move the dish antenna to different satellites or orbit locations. Problems are common in this setup for many different reasons. The actuators and dish movers that most of use are made from the cheapest materials available.

The average dish mover is rated at around 80 watts of output power. This equals to roughly 2 amps at 36 volts. Most of our dish movers are rated at 36 volts dc, which is True, but this voltage will collapse or fall a great deal once a load is introduced. In most instances, the voltage will decrease, and the amperage will increase once the dish starts moving. This is why you see dish movers rated at 3-5 amps. This amperage amount is only seen under a load, and the total amount of power in watts will rarely go over 80 watts in most fta dish movers.

Most fta actuators have a screw inside the actuator shaft. These screws are not coated and are known to rust. A rusty screw is hard to turn. The fta actuator will have a set of gears located between the motor and the screw. These gears may reduce motor speed, and allow more energy to be availabe to turn or move the dish. These gears are usually made from composites or materials that closely resemble plastic. These gears will run a long time, but will become stressed when the actuator screw binds.

It is probably safe to say that the majority of dish moving issues in a fta system are a combination of things.
A dish that will not stop at the same spot every time could have a faulty reed switch, a faulty brake system, or a dirty power supply in the dish mover.The wiring that goes from the dish mover to the reed switch could also be the problem.
A dish mover that throws errors and does not complete the desired or called move may have an actuator binding or a bad power supply inside the dish mover.
Dish moving issues will usually start slowly or not be real noticeable. For example, it may take longer for the dish to move a great distance, but everything else is ok, or we may notice a weak signal on a certain satellite and change the dish position to fix it. If these issue are not corrected when they first appear, then it is highly likely other additional problem will exist before anything is fixed.

I will attach some pictures and explain how to fix some common issues in the following posts of this thread.

Here is a picture of an actuator with parts removed.
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The screw on this actuator is rusted, which will cause binding.
A dish mover has to work extra hard to turn something like this.
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Most fta actuators can easily be checked for binding or rough spots in the screw. The easiest way to check is by attaching a volt and amp meter to the dish mover, then move the dish from one end of the arc to the other while watching the volts and amps. The voltage should stay about the same at all times, or at least within a few volts. The amps should steadily increase or decrease as the dish is moved from one end of the arc to the opposite end. Always start this test at one end of the arc, with the dish at the lowest point possible.Binding will show up in the volts or amps as spikes.

The motor itself should be tested in actuators that bind or in actuators that have rough spots. The motor is attached to the transmission and may easily be removed from the actuator. Repeat the volts and amp test on the detached motor. The amps should be steady at start-up and should not changed when the motor is moved from one end f its travel to the opposite end of travel.

If a volts and amp test is not available, then the dish may be observed while moving from the opposite ends of the satellite arc. The dish should not jerk or jump. The amount of force that is needed to move the dish may be found by removing the motor and manually turning the screw by hand. Watch the dish move from the opposite ends of the arc more than once!

A dish that jerks or jumps while moving may have bad polar mount bushings.

A cure for a binding actuator may be simple. Some actuators will have a drip or weep hole close to the motor. This hole should be facing or pointed down, and it allows for moisture removal. Actuators that are binding or ones that have rough spots may be fixed by purchasing a spray can of WD40 and a spray can of white lithium grease. Remove the actuator, turn it upside down and spray WD40 into the actuator tube and directly on the actuator screw. The screw is located in the center of the tube, and the spray can be directed through the weep or moisture hole. If no hole exists, then drill a small hole, being certain that the hole will face down when the actuator is installed.. Follow the WD40 bath with the lithium grease. I prefer to use liberal or large amounts of both WD40 and lithium grease. This is a sealed unit, and attracting dust or dirt to the screw inside the housing should not be an issue. White lithium grease generally will not cause binding issues in cold weather or cold climates. The only alternative to cleaning and greasing is to replace the actuator.

An actuator that does not stop at the same location every time may need the reed switch replaced. It is also possible that the transmission could be damaged (common in binding actuators), or the motor brake system may be faulty.

Both the Vbox and Gbox dish movers are made from the cheapest parts available, but they will usually work for a long time if the actuator does not have any issues. These dish movers may also be referred to or called positioners. Heat was never really thought about in the design of these two dish movers. Using an external power supply will be a good idea for some dish systems.

Most fta actuators are designed to operate between 24 and 36 volts using dc current. Power supplies are sold on Ebay and at other locations that will produce 24-36 volts all day, and at current ratings of up to 10 amps. These power supplies will normally cost under 50 dollars. I purchased a pair of 24 volt supplies on Ebay for under 50 dollars shipped. The 24 volt supply I chose can produce around 8 amps at 27 volts dc.

The basic procedure for installing a power supply into an existing Gbox or Vbox is simple. What is described here assumes that you know the basics of electricity to keep from being shocked or electrocuted.

Remove the pc board from the case, and reconnect ac power. Probe the outputs of the transformer with an ac volt meter. There should be four wires on the transformer output. The low side drives the dish mover controls and chips, while the high side provides the power to the actuator. Both sides of the transformer outputs are ran through circuits to change the power from ac to dc. One way to install an external power supply in the dish mover is to cut the high voltage outputs of the transformer, then solder the wires for the external power supply directly to the relays on the dish mover pc board. There are two relays, one for each direction of travel. The actuator motor is a dc motor. The motor has two leads and will move in one direction when dc voltage is applied to the two leads. It will move in the opposite direction when the two leads are reversed, This explains the need for two relays.The relays are usually rated for 10 amps which is more than most of us need. (We will continue in the next post with pictures)

Here is a picture showing the output wires of a transformer.
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Locate the two 5 pin relays
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The two pin side of these relays should have around 36 volts dc or more with the dish mover plugged in and running, but not trying to move anything. In other words, these two relay pins should have 36 volts dc or better at idle.

Here is the back side of the pc board
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I flipped the pc board and probed it for voltage while it was plugged in. Be very careful if you do it this way. and you may damage the dish mover if you short something out while probing!
Remove AC Power. Solder four wires, two for each relay.
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These pictures were taken during tests. Use care and caution, plus good installation techniques if you solder to the back of the pc board like this. There are other ways to do this, but it will work fine as shown.


Make sure the soldered wires are not shorted. Apply AC power. Measure for dc voltage on the newly soldered wires. Note and mark the correct polarity for each wire(+-). Remove AC power. Cut one wire on the transformer high side output. Apply ac power. Verify that no dc voltage exists on the soldered relay wires. Remove ac power. Cut the other high side output on the transformer, then remove the fuse on the pc board if it has one.

Reassemble the dish mover, and make provisions to run the new wires outside to the external dc power supply.

Here are some pictures of my external power supply.
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Here are some pictures of my actuator motor with transmission.
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The work described in this thread was done on or for a 3.6 meter commercial dish. The actuator on this dish is good quality, but it had sat for a number of years, which caused rough spots in the actuator screw. The actuator motor was pulling 5 or more amps at the extreme ends of the arc. The actuator was removed from the dish and cleaned as describe in this thread. There was also a problem in the transmission or the gear set that is located between the motor and actuator. The transmission was replaced. Amperage draw at the extreme ends of the arc on startup now are between 2 and 3 amps. So the cleaning and replacing the gear set cut the amperage draw about in half.

We do not see much snow and ice here. I would expect to see current draws of around 5 amps at startup If the dish was loaded wit snow and ice, and if the dish was near one end of the arc. Current draws of around 1-2 amps or less are common when moving 20 degrees or less on either side of center or due south.

I also purchased and installed a digital hall effect amp meter, and two digital dc voltage meters (one for each direction). It would be nice to mount all of this stuff in one neat box someday. I would be nicer if someone actually sold a dish mover that had these features. I am convinced that watching the voltage and the current draw in amps while the dish moves is the best way to see problems in the system. I will know when it is time to grease the actuator screw because the amps will climb above what they are now while the dish is moving. My Gbox dish mover stays cool at all times, and has no issues since I installed the external power supply for the actuator. Questions or comments about this subject are welcomed.EB

Very informative EB thanks. There is another situation happening up here on occasion is that the DC motor magnets brake away from the housing, therefor must be epoxied back on. Done a few in the past.

You also need to take into consideration the size of the wire gauge going out to the motor from the positioner, if the wire gauge is too small the DC voltage at the motor will drop.

AWG* for most installations should be a #12 gauge, a smaller gauge can be used for short runs of up to 25 feet, but the bigger the power wires the less DC voltage drop there will be, you must remember that the DC current will always be the same (lets say 4 amps) but the DC voltage can vary, if the power wires are too small and too long the DC voltage can drop too much and your motor will slow down.

At 50 feet a #12 gauge wire will loose .64 volts at 4 amps draw, a #16 gauge wire at 50 feet will drop 1.6 volts, a #20 at 50 feet will drop 4 volts, so you can see that the larger wire will drop less.

Here is a calculator to help with how big a wire would be needed for the less voltage loss on your system.

Code:

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http://www.calculator.net/voltage-drop-calculator.html?material=copper&wiresize=33.31&voltage=36&phase=dc&noofconductor=1&distance=50&distanceunit=feet&amperes=4&x=45&y=13

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Most "C" band siamese ribbon cable has a #16 conductor for the motor, this would work out OK for runs under 50 feet or so, anything longer and I would recommend a separate set of larger conductors for the motor.

*AWG = American Wire Gauge, the smaller the number the larger the diameter of the conductor, so a #16 is smaller then a #12, the larger diameter conductor will have less DC voltage loss on a longer run.

I've been having some fun working with old antenna positioners from the 80's, These units were built strong and built to last. They have everything a VBox doesn't and a VBox has what these old movers didn't have, a brain. I picked up a DX Antenna Co. DSB-300 power supply, a "side car dish mover" that needs the matching analog receiver to run it. This unit has a beautiful steel case and a 180 watt toroidal transformer to power it. A VBox 7 has a 2A fast blow fuse protecting the motor power circuit. The old DSB-300 uses a 6.25A Slow blow fuse to protect the same circuit. The DSB transformer definitely has more power than a VBox. So I decided what I need to do is combine the DSB-300 with a VBox and have the best of both worlds. :) Ends up looking like this:

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There are several ideas on antenna positioners out there. One interesting plan is to use your cellphone to control the unit.
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But this is just the control circuit and requires you to build the power circuit. It designed to run off a 24V transformer so there are some old antenna positioners that really would work well for this project.
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Even the board I took from the DSB-300 has some possibilities here.

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