Receiver Won't Hold Position Counts

[milano maroon]

I am using a DSR-920 and a Thomson Saginaw linear actuator with what I think is a reed switch. It has a disc with 4 magnets and a barrel type sensor with two wires out. My problem is it doesn't return back to the correct satellite position even though the counter is correct. Seems like it travels farther than it should which leads me to believe it is missing counts?

Actuator ground (drain wire is good). Also have tried moving the sensor closer to the magnet wheel.

When these sensors fail do they fail completely? Or can they still output counts sporadically?

Anyone know where I can find a replacement sensor? Skyvision has them but they are $30 to $40 plus shipping. Digikey has some barrel sensors for $4 but they are too small to thread into the bracket.

Should I look for one Normally Open or Closed?

Thanks for any help you can give me,

Jeff

 

[Mr Tony]

moved thread to 4DTV area where more folks can see it and help out

 

[Inno]

Normally open I would think although it shouldn't really matter. I would guess that it is missing counts too. It could be that the magnet wheel is too far away from the reed switch, I have had that happen..........by the same token if it is too close to the reed switch it may be missing counts as well and staying closed between two of the magnets if they are maybe a little stronger than the others.

In a situation like this I will take my multimeter to the dish and connect it to the reed switch contacts with a set of alligator clips. Set it for the lowest resistance or continuity setting if it has one. Then I will rotate the magnet wheel by hand (it will slip on the shaft) and see what is happening. Often times a small adjustment in or out with the magnet wheel on the shaft is all it takes to bring the magnets to the proper location in relation to the reed switch.

If all that fails, or if you can get some improvement, order a new switch anyway. As a mechanical device it is eventually going to wear out .

Oh and to Satellite Guys!! Great to have you here.


As to whether they fail completely, I have had them get a little flaky in that the contacts stay together. In these cases though the dish moves a little but the receiver is not seeing any pulses so it will give you an error. A sharp tap with the handle of a screwdriver will usually get it working temporarily.

 

[milano maroon]

Thank you for the reply. And thanks for the welcome to the forum.

Do you think we can at least rule out a problem with the receiver missing the counts?

One thing that I haven't figured out - what generates the pulses? I don't have the 5v output on the back of the receiver hooked up to anything. I understood that this was to provide power to an optical sensor. My sensor has two wires, one goes to Pulse and the other to Grd. So where does the pulse come from?

I will try moving the sensor closer/farther and see what happens.

 

[Inno]

In a system like that all it is really doing is making and breaking a contact between the pulse and ground..........when you ground the pulse line, it's circuitry counts a pulse. You are probably bringing a logic circuit from high to low when the switch is closed thus counting one pulse.
Yes, the 5V was for the old optical sensor type units which were more prone to problems from static or lightning.

I would not suspect the receiver as a problem at this point. If you wanted to confirm this you could hook a momentary push switch between GND and Pulse on the receiver then open and close the switch quickly as you tell the receiver to move the dish............unhook the motor wires first so you are not throwing your alignment out of whack.
Then tell the receiver to move the dish in the opposite direction and pulse the switch again until the count goes back to where you started..........you should see the number increase by one with every button push. I don't think I have ever seen a receiver problem that causes lost counts, it has always been with either the switch, magnet wheel or wiring.

 

[milano maroon]

Thank you for the replies so far. Still haven't got it figured out yet. Here's what I have tried.

I removed the actuator today, took the reed switch out, and checked each of the 4 magnets with another magnet. One seemed to be a little different (N/S poles were on opposite edges instead of opposite faces like the other 3. So I replaced all of them with new magnets, turned my continuity test on tone and ran the actuator with a car battery charger. It seemed like I got even pulses every time a magnet passed under the switch.

So I put everything back together, re-installed the actuator and remapped some satellites. Going from G4 to G1or G1 to G4 I go beyond the satellite. Turns out I go beyond by 25%. So I guess out of 4 magnets if I had one weak one that would account for the problem. Yet when I checked it on the bench they all sent a pulse. I thought perhaps the wheel might be slipping on the shaft so I put a dab of silicone on before I pushed it into the shaft. Perhaps the slower speed on the bench (12v vs more from the 4DTV) allows better switch performance.

Dish is tight, cable is dry (except for 10 feet outside at the dish, and drain wire is grounded. The fact that it is repeatably off 25% seems to rule out an intermittent issue like a cable or slippage.

Any ideas? I could try moving the sensor distance to/from the magnet wheel but the minimum distance is fixed. I can't get it any closer because it rides on the edge of a plastic disc that sits on top of the magnets. Try increasing the distance?

I am totally baffled. Any more help would be appreciated.
Thanks,

Jeff

 

[Inno]

Increasing the distance would be my next move. Just how much I really can't say.
When you say you replaced the magnets, where did the new ones come from?
I would say that being as how the magnets that were in there worked at one point that they should be fine. Magnets don't just change in strength.
If the magnets were too close to the switch it may be that the switch is being held closed and not opening between two of the magnets..........yes, the speed change brought on by a higher voltage from the 922 may make a difference.

So with your 25% figure, if you ran the dish back and forth again a second time does that increase your figure another 25% or does it go to the same position every time only it is the wrong position? And lets say you go from G4 to G1, where does the dish end up? Is that the same every time or does it increase?

The other thing could be a worn out switch, it may be at higher speeds it is simply not opening between magnets. I have seen them become sticky before. I would probably be changing the switch at this point just so you don't drive yourself crazy.

 

[Radioguy41]

Here is a copy of some info I got off the web several years ago, I don't remember where. The actuator that seemed to be the most troublesome was the Von Weise. There is some more info in this archive:

http://anubis.macross.com/~drlev/6511.1.htm

ACTUATOR LOSES SATELLITE POSITIONS

If you notice you continually have to adjust the satellite position you may have an actuator grounding issue. This problem has been noticed on some of the “faster counting” actuators. It does not indicate the actuator is bad however. As the actuator turns the sensor sends a count of the rotation back to the receiver. The problem is the sensor moves faster than the receiver can pickup.

Here are three fixes for this situation, the first is the easiest, the second and third is a little harder.

1. Use one of the unused wires in the actuator bundle of wires coming from the dish and secure it to the threaded post on the back of the receiver. Secure the other end to a mounting screw in the actuator motor case. Do not secure it to the terminal strip that has the motor and sensor wires attached to it.

2. Shim the sensor out from the Magnets if it is that type of actuator.

3. Remove one of the magnets.

 

[tvropro]

I have a Saginaw if it's like mine (see picture) it's not a high count unit. Connecting the drain wire on my Saginaw makes it miscount. If you have it connected you may want to disconnect it.

I have a very small gap between the magnets and switch.

Mine hits dead nuts on every time hooked up as it is.