Polorotor Help?

Captain Midnight

Captain Midnight

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SatelliteGuys Pro
Sep 16, 2019
543
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Greers Ferry, Arkansas
I am typically a LNBF or orthomode feed guy, but I came across a dish with a C/Ku Chap Corotor feed that I got free. I scored a Pansat 3500 for $10 on ebay for the skew control. Not many DVB-S signals left, but enough for me to try out the feedhorn. I tuned to 101w and ran a blind scan with the receiver connected to my orthomode feedhorn. The receiver found the DVB-S signal and Daystar SD actually played. Nothing else because the Pansat only decodes MPEG video. I can still see the MeTV and other FTA signals on the signal meter. I connected the C/Ku feedhorn in the house at the receiver to test the skew control...

Here's the issue:

When I am tuned on a Horizontal transponder, the servo motor jumps around 10 degrees or so rather constantly, even with the receiver in StandBy. The servo is stable and adjusts smoothly on Vertical transponders.. I'm not sure the issue.

Advice? I can video the servo probe if it will help.
 

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primestar31

primestar31

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Try connecting a 1000 µF 5 volt (minimum rated) electrolytic capacitor between the +5 V and ground wires at the servo motor. The capacitor prevents any voltage drop between the controller and the servo, eliminating the servo motor studdering after channel or polarity changes.
 
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arlo

SatelliteGuys Pro
Dec 4, 2016
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Just because, open the servo and spray the potentiometer with some good contact cleaner.
Not a lot, just enough while you run it through the rotation kinda' fast.
If you have and can use a multimeter check for a smooth resistance sweep throughout the movement.
Clean and lube the gear train it so it operates nice.
 
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Captain Midnight

Captain Midnight

Thread Starter
SatelliteGuys Pro
Sep 16, 2019
543
369
Greers Ferry, Arkansas
Try connecting a 1000 µF 5 volt (minimum rated) electrolytic capacitor between the +5 V and ground wires at the servo motor. The capacitor prevents any voltage drop between the controller and the servo, eliminating the servo motor studdering after channel or polarity changes.
Is that what these are? I always see these things at the servo motors.
 

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A

arlo

SatelliteGuys Pro
Dec 4, 2016
812
502
North Eastern
Just because, open the servo and spray the potentiometer with some good contact cleaner.
Not a lot, just enough while you run it through the rotation kinda' fast.
If you have and can use a multimeter check for a smooth resistance sweep throughout the movement.
Clean and lube the gear train it so it operates nice.
I dug this picture up from Ricks. Don't make me RE one of the servos I have.
Look in the feedhorn. See if in fact the probe snaps to the H-V positions.
A pulse from the receiver or mover tells the servo to go H or V.
The dude that tells determines probe position is the feedback potentiometer.
Think of a rotary volume control that goes scratchy or has dead spots in volume.
If the servo circuitry is looking for ~100 ohms for H and ~1250 ohms (only an ex.) for V.
As the gears spin which also rotates the feedback device (pot) and the probe is rotating in the feedhorn. And the pot has a range of 0-2500 ohms.
With the circuitry looking for a resistance match. The pot is dirty, defective......has a dead spot(s).
What happens? The servo stops or starts hunting trying to get what it takes to satisfy the circuitry.
Heaven forbid the same thing happened to an RC airplane or chopper and gave the neighbors dog a haircut!
Or kept right on going to Kansas.
Look at the notes.

1659799364306
 
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Captain Midnight

Captain Midnight

Thread Starter
SatelliteGuys Pro
Sep 16, 2019
543
369
Greers Ferry, Arkansas
I dug this picture up from Ricks. Don't make me RE one of the servos I have.
Look in the feedhorn. See if in fact the probe snaps to the H-V positions.
A pulse from the receiver or mover tells the servo to go H or V.
The dude that tells determines probe position is the feedback potentiometer.
Think of a rotary volume control that goes scratchy or has dead spots in volume.
If the servo circuitry is looking for ~100 ohms for H and ~1250 ohms (only an ex.) for V.
As the gears spin which also rotates the feedback device (pot) and the probe is rotating in the feedhorn. And the pot has a range of 0-2500 ohms.
With the circuitry looking for a resistance match. The pot is dirty, defective......has a dead spot(s).
What happens? The servo stops or starts hunting trying to get what it takes to satisfy the circuitry.
Heaven forbid the same thing happened to an RC airplane or chopper and gave the neighbors dog a haircut!
Or kept right on going to Kansas.
Look at the notes.

View attachment 157863
Do you know if the servos have limits or can they turn 360? This one will run about 90 degrees really well and then hit a "scratchy" area. Then I can drive it further a bit and it stabilizes again.
 

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pacificrim

pacificrim

SatelliteGuys Pro
Oct 5, 2008
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Make sure to use a shielded wire with a drain connected to your mover' ground. I used regular CAT 5 for bench testing but had some weird groaning coming from the servo and it wasn't accurate in switching polarities. I switched it to shielded with a drain wire and the issue went away. Even 10 feet of unshielded wire was enough to throw it off.
 
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Captain Midnight

Captain Midnight

Thread Starter
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Sep 16, 2019
543
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Greers Ferry, Arkansas
Motor on my actual c/ku horn is running much better than the first horn I tried. Only tried it because it has an extra 3ft of wire on the motor... Here is switching from H to V.
 

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Titanium

Titanium

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As Pacificrim stated, PCM servos are very suseptible to interference. In this case, i would remove the servo and observe the rotation for smooth movement and landing on position and staying in place with no stutter without the probe attached. If the servo still has same problem, attach directly to the controller (without the distribution cable) and retest. Some brands of servos have internal capacitors to help mitigate line noise. If the servo remans glitchy, servos do fail and it may be time to replace.

Check the feedhorn probe for smooth rotation. Some models freely rotate, others have stops. If the probe has rotation stops, be sure the probe is centered prior installing the servo. Carefully clean the probe mount before reassembling. The plastics brittle with age.
 
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arlo

SatelliteGuys Pro
Dec 4, 2016
812
502
North Eastern
Do you know if the servos have limits or can they turn 360? This one will run about 90 degrees really well and then hit a "scratchy" area. Then I can drive it further a bit and it stabilizes again.

I dug this picture up from Ricks. Don't make me RE one of the servos I have.
Look in the feedhorn. See if in fact the probe snaps to the H-V positions.
A pulse from the receiver or mover tells the servo to go H or V.
The dude that tells determines probe position is the feedback potentiometer.
Think of a rotary volume control that goes scratchy or has dead spots in volume.
If the servo circuitry is looking for ~100 ohms for H and ~1250 ohms (only an ex.) for V.
As the gears spin which also rotates the feedback device (pot) and the probe is rotating in the feedhorn. And the pot has a range of 0-2500 ohms.
With the circuitry looking for a resistance match. The pot is dirty, defective......has a dead spot(s).
What happens? The servo stops or starts hunting trying to get what it takes to satisfy the circuitry.
Heaven forbid the same thing happened to an RC airplane or chopper and gave the neighbors dog a haircut!
Or kept right on going to Kansas.
Look at the notes.

View attachment 157863
Okay you made me do it. Look at the pics. The positional pot is attached directly to the probe coupler.
Yes. The probe will rotate 360 degrees with the servo disconnected. The coupler is keyed to the pot.
So. No screw-up can happen there.
The 4 screws were a bear to get out. PB Blaster and a very good fitting #1 Philips screwdriver is needed.
And time.
I'm very positive that if you clean the pot that the thing will straighten up. Pull the middle gear so you can rotate its shaft. And don't lose that pin.
Is it "jittering"?
I mean after umpteen years the capacitor(s) could be borked. I dont know. Cleaning several pots in the past did straighten things up.
The gear train has pins that might fall out. So do it all on a microfiber so you don't end up cussing the carpet.
20220806 163416
20220806 163353
 
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Captain Midnight

Captain Midnight

Thread Starter
SatelliteGuys Pro
Sep 16, 2019
543
369
Greers Ferry, Arkansas
Well I appreciate the advice. I can now say I have operated a feed with a servo. The experience has been good, but I prefer having a dedicated dish for Ku band. I am not sure how good the ku LNB on my 20 year old horn is... but the C Band LNB works very well for being so old.

I also noticed my Ku signals peak about 2 counts off of my C band signals. Is this common?
 
primestar31

primestar31

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I also noticed my Ku signals peak about 2 counts off of my C band signals. Is this common?
Yes. The fix is to repeak all the dish adjustments using the KU signal (as it's a tighter beam), IF the KU feed is also centered in the feedhorn like the C-band. IF you do it that way, then the C-band which is a bit more forgiving will take care of itself.
 
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Captain Midnight

Captain Midnight

Thread Starter
SatelliteGuys Pro
Sep 16, 2019
543
369
Greers Ferry, Arkansas
Update: I have some adjusting to do if I want to receive reliable ku
Yes. The fix is to repeak all the dish adjustments using the KU signal (as it's a tighter beam), IF the KU feed is also centered in the feedhorn like the C-band. IF you do it that way, then the C-band which is a bit more forgiving will take care of itself.
Yeah, I did some adjustment today and realized my dish mount was off azimuth, not facing true south. I went through a lot of back and forth, fighting with it. I can get stronger Ku signals to lock, albeit with low signals. I am not giving up yet, just discouraged with the amount of struggle it has been. My dish has few deformities but it really is struggling. And I'm not sure about the 20 year old Ku LNB on the feedhorn. Might be holding me back to say the least. The C Band LNB is very stable for its age.


Biggest peeve is my mount is wanting to be set to 35.2 degrees for elevation but my location should use 35.9 degrees. My declination is about 5.1 degrees, as the charts recommend. I checked my feed and made sure it is at the same angle as my dish center.
Anything else I can check? Post is plumb.
 
Captain Midnight

Captain Midnight

Thread Starter
SatelliteGuys Pro
Sep 16, 2019
543
369
Greers Ferry, Arkansas
I also noticed at times, the servo motor would sometimes start turning randomly. I could only get it to stop by turning the probe by hand back to the selected polarity. Then it would suddenly relax and work fine for another hour or so. Is this just from an old motor or were these servos always kinda screwy? Or is it because the Pansat 3500 I'm using for skew control has no DVB-S signal available on some satellites?
 
Last edited:
A

arlo

SatelliteGuys Pro
Dec 4, 2016
812
502
North Eastern
I also noticed at times, the servo motor would sometimes start turning randomly. I could only get it to stop by turning the probe by hand back to the selected polarity. Then it would suddenly relax and work fine for another hour or so. Is this just from an old motor or were these servos always kinda screwy? Or is it because the Pansat 3500 I'm using for skew control has no DVB-S signal available on some satellites?
the servo motor would sometimes start turning randomly
Clue #1:
The controlling circuitry is glitching the motor into jittering. Perhaps only reaching one polarity and not the other.

could only get it to stop by turning the probe by hand back to the selected polarity
Clue #2:
You moved the potentiometer that is connected directly to the probe coupling.
Which provides positional feedback to the motor control circuitry.
When the circuitry reads a particular resistance from the potentiometer, the motor is shut off.
The receiver only knows that a given transponder is horizontal or vertical.
That's stored in the settings for satellite/transponder mapping. Satellites.xml in the E2 world.
Nothing provided in the signal would tell the receiver to switch polarities.
Please either replace the servo or do what I suggest above.
Try disconnecting the pulse wire while the servo is having seizures.
If it stops then I'm incorrect. If it continues then the problem is in the servo.
If it were me I would have put a multimeter probe on the outer 2 pot terminals looking for...
oh, that's right you made me open one up.
Outer terminals in circuit read 4.38 k. Ohms.
Center to outer terminal sweeps from 0 - 4.38 k Ohms as you rotate the pot.
Smooth increase/decrease in resistance. No spots where the meter jumps to infinite resistance.
The beauty of using an analog meter. Or digital bargraph.
I wish you luck my friend. Not enough troubleshooting going on here. And too many assumptions.
"A Parts Cannon" in the automotive world.
 
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Captain Midnight

Captain Midnight

Thread Starter
SatelliteGuys Pro
Sep 16, 2019
543
369
Greers Ferry, Arkansas
the servo motor would sometimes start turning randomly
Clue #1:
The controlling circuitry is glitching the motor into jittering. Perhaps only reaching one polarity and not the other.

could only get it to stop by turning the probe by hand back to the selected polarity
Clue #2:
You moved the potentiometer that is connected directly to the probe coupling.
Which provides positional feedback to the motor control circuitry.
When the circuitry reads a particular resistance from the potentiometer, the motor is shut off.
The receiver only knows that a given transponder is horizontal or vertical.
That's stored in the settings for satellite/transponder mapping. Satellites.xml in the E2 world.
Nothing provided in the signal would tell the receiver to switch polarities.
Please either replace the servo or do what I suggest above.
Try disconnecting the pulse wire while the servo is having seizures.
If it stops then I'm incorrect. If it continues then the problem is in the servo.
If it were me I would have put a multimeter probe on the outer 2 pot terminals looking for...
oh, that's right you made me open one up.
Outer terminals in circuit read 4.38 k. Ohms.
Center to outer terminal sweeps from 0 - 4.38 k Ohms as you rotate the pot.
Smooth increase/decrease in resistance. No spots where the meter jumps to infinite resistance.
The beauty of using an analog meter. Or digital bargraph.
I wish you luck my friend. Not enough troubleshooting going on here. And too many assumptions.
"A Parts Cannon" in the automotive world.
That's why I come here. So I can ask the people smarter than me how to troubleshoot the problem. Thanks for the information.
 

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