Trouble with skew control

[royrose]

I have BUD system that works perfectly except that I can't adjust the skew (except manually at the dish).

My system: 10ft fiberglass dish, Chaparral Corotor II feedhorn with C and Ku LNBs, 4DTV to move dish and adjust skew, Amiko Mini SE tuner.

I recently received a new servo motor from Titanium Satellite, wired it up and confirmed that the 4DTV can get it to turn. When I screwed the motor into place, however, It moved the skew a bit but then wouldn't move it either way. This is the same problem that I had before. When I then pulled the motor off, the slotted piece of plastic that the skew motor connects to came off with it, so that piece is obviously not connected to the metal device that determines the skew.

The dish and Corotor are about 35 years old.

Most of the time, I watch NBC on SES 3 (W1) in order to see the news or other shows early so I manually re-set set the skew at the dish for that. I would, however, like to restore my ability to tune all channels.

Here is a picture of the piece that came off.

Any suggestions?

 

[Titanium]

This is the connector shaft between the servo and the probe. It appears to have broken? There was one design that it was removable with slots to align. If it is removable, align the slots and reassemble. If a broken shaft, align and repair with epoxy.

 

[. Raine]

When you put it back together, make sure that the probe isn't frozen up or sticking. Mine froze solid before, a bit of silicone spray freed it up. It wiped out two servos before I realized it though, the small brass gear (internally) had spun off the motor shaft on both servos.

 

[Magic Static]

I had that plastic part break on a corotor too. Glued it back together. I surmised there was some ice buildup that stuck the probe and it broke, but not for sure. make sure you align the break correctly when gluing.

 

[royrose]

Thanks for all of your quick responses. I thought it could be a break but I was confused by how clean the broken end is. It looked like there are slots holding the probe in place, so I will try to get it out tomorrow.

The silicone spray sounds like a good Idea. I think it may have been hanging up which may have contributed to the break.

I'll report back on how it goes.

 

[waylew]

Did you check the feedhorn for a wasps nest? They love to build nests up inside and then the probe can't turn.

 

[Cham]

In my corotor the probe appears to be attached to the plastic bushing (pictured) and won't come out. This is a 10 yr old unit and might be different. Can you try to take a picture of the probe inside the feedhorn (especially at the back of the feed horn)? I am thinking the probe might have to be glued or epoxied to the plastic bushing which would require some care and precision so not to epoxy the bushing to the housing, or leave too little clearance between the probe and the back of the feed horn causing the assembly to bind...

Maybe the probe assembly can be removed and re-assembled (glued) and re-installed as a unit from behind or from the feed opening?

I have never taken mine apart so not completely sure on that...

 

[royrose]

In my corotor the probe appears to be attached to the plastic bushing (pictured) and won't come out. This is a 10 yr old unit and might be different. Can you try to take a picture of the probe inside the feedhorn (especially at the back of the feed horn)? I am thinking the probe might have to be glued or epoxied to the plastic bushing which would require some care and precision so not to epoxy the bushing to the housing, or leave too little clearance between the probe and the back of the feed horn causing the assembly to bind...

Maybe the probe assembly can be removed and re-assembled (glued) and re-installed as a unit from behind or from the feed opening?

Mine looks very much as you described. Here are a couple of pictures: It looks like the plastic three legged piece holding the probe in place would slide out but it feels very firmly in place.

I also found this on the Chaparral web site: "pull up gently on the amber colored drive shaft that couples to the servo motor. If the shaft pulls out, you will need to send the entire feed to Chaparral for repair." So, I will contact them but I will have to decide whether it is worth going through all of the steps to get it repaired or replaced. You would think that they would make a set of parts that could be installed by a user/installer.

 

[Cham]

Yea... like Brian says above maybe take a chance and try to epoxy it to the probe in the bottom of the hole... Maybe have an LNBF on hand first in case it doesn't work out. I suspect trying to remove the probe would end up breaking the plastic holder below the Ku section.

 

[royrose]

well, I was very positively surprised when I heard back from Pacific Tech Satellite, the distributor for Chaparral. It turn out that the units with the amber plastic piece had a defect that was corrected in later units. Chaparral is replacing my Corotor with a new one at no charge! That is after 30+ years. Now I don't have to worry about the probe binding because of wear. I am happy to pay to ship my old unit back to them. That is the best customer service I have received on any product ever.

My only question: As I explored this issue, when I examined my feedhorn, it looks like the probe cannot rotate more than 180 degrees before hitting a stop. When I install the new feedhorn and then turn on my 4DTV, Will the skew motor rotate the probe to the position set by the 4DTV and therefore be able to travel the 180 degrees without hitting the stop? Or do I have to do something to to align the skew at the dish with the setting on the 4DTV? For example, if the 4DTV skew setting is 0, will I be able to safely go 90 degrees in either direction?

I hope that question makes sense. I don't want to screw up the new Corotor.

 

[Titanium]

Incredible customer support! Great to hear!

The rotation between polarities only requires 90 degrees of rotation. The feedhorn is installed with the servo detent "resting" position with the long edge of the servo body aimed at approximately 10:30/11 o'clock position to the polar axis of the dish. This position aligns to the centered offset position for most IRDs and the ASC1. Example: the ASC1 is calibrated to place the polarity probe in the Horizontal or Vertical polarity with the default +45/-45 degree settings when the feedhorn is properly installed.

Use the Chaparral feedhorn install template on the last page of the install guide to easily set the feedhorn at the correct angle.

 

[royrose]

The feedhorn is installed with the servo detent "resting" position with the long edge of the servo body aimed at approximately 10:30/11 o'clock position to the polar axis of the dish. This position aligns to the centered offset position for most IRDs and the ASC1. Example: the ASC1 is calibrated to place the polarity probe in the Horizontal or Vertical polarity with the default +45/-45 degree settings when the feedhorn is properly installed.

Use the Chaparral feedhorn install template on the last page of the install guide to easily set the feedhorn at the correct angle.

Well I removed the old Corotor and sent it off to Chaparral. I have a couple more questions.

1) the instructions say to attach the scaler ring to the mounting bracket on the dish. My Corotor was mounted using a collar holding the body of the Corotor with the scaler ring attached to the Corotor but otherwise free floating. I was planning on mounting the new unit the same way because that would position the Corotor as it was before. Any problem with that? See picture below.

2) My Corotor appears to have been installed at 180 degrees from the way pictured in the instructions, with the C band LNB up and the Ku band LNB down. Does that matter? If so, should I do it the way it was before or with the Ku band LNB up. It does seem to have been in line with the 10:30/11:00 position.

3) Still trying to fully understand how the skew control works. What I am getting from your description is that the Corotor will arrive with the probe in the resting position (assuming the correct 10:30/11:00 position) and then will go to the last preset skew position when the IRD is wired up and turned on. When the IRD is turned off does the servo motor return to the resting position and then go back to the preset skew setting of the satellite the dish is aimed at or does the the servo motor stay at the last set position when the IRD is turned off?

Thanks again.

 

[Titanium]

1. If mounting the new feedhorn in the bracket provides the correct FD ration setting and Focal Length, yes. Use the clamp. Don't trust that the "last guy" installed the feedhorn properly. Measure teh dish diameter and depth and calculate the FD ratio and Focal Length measurement. Does it jive with the current setting?

2. No matter if the feed is rotated 180 degreesfrom the template. Vertical is still vertical and horizontal is still horizontal.

3. The servo will stay parked at the last setting. It does not rotate to a different position when power is removed. The positioning is performed via PCM calculated from a detent centered position. It does not need to return to that position to calculate offset changes. One thing to note, if the servo picks-up power from another source (example: when the actuator motor power is engaged) it may momentarily rotate out of position until the common mode power is no longer present. This is a very common problem for servo motors and robotic builders deal with this problem a lot. The cause is usually poor shielding of the servo circuit or distribution wiring. I would often run accross this problem during C-band service calls if the customer used 3 conductor non-shielded wires for the skew control or the shield's drain wire was not attached to the IRD or controller ground terminal.

 

[royrose]

Very clear explanation. I believe that I will be able to mount the new feedhorn at the exact position of the old one but will indeed check the measurements as a learning experience. I'll report back when I get the new Corotor.

 

[royrose]

O.K. I got the new Corotor and did mount it in the same spot using markings that I had made. I didn't calculate the FD ratio and focal length because I immediately got strong signals in C and Ku band, both horizontally and vertically throughout the arc. The guys that installed my dish many years ago did a good job.

The only thing that was off was the rotational position. Initially, vertical was near zero degrees and horizontal near 90. I think it was like that with the old set up as well. I was able to easily correct that by rotating the feedhorn until I got strong signals at +/- 45 degrees and then clamp the feedhorn in place.

So, now my setup works great and is a pleasure to use. Hopefully I won't have to mess with the dish for a long time. And in the process I learned a lot and will be better able to trouble shoot any problems that do come up.

Thanks again for all of the help.