"Sticky Tuning Knob" - Overhaul of Ten Tec Omni VI Plus Tuning Knob

From the Ten-Tec Reflector May 7, 2006

My Omni VI Plus main tuning knob had binding over a 90-degree section of rotation, from 9 o'clock to 12 and it took all the fun out of tuning the bands.

Posters in the Archives have discussed repair of a sticky Omni VI tuning knob, but this post goes into step-by-step detail and addresses an unexpected cause of knob binding.

This post is probably useful to earlier Omni owners (and possibly Orion and other Ten Tec owners as well).

  1. I disassembled my main tuning knob by first gently pulling forward the roughened "grip" rubber strip. Once off, remove a 1/8 inch "rubber band". (Put all parts in zip lock bags as you disassemble.) Now, you can use a 1/16 English Allen wrench to loosen the set-screw, and the knob comes off by pulling gently forward. Once off, you can turn the knob inside the silver skirt, and you will see two copper tabs that are spring loaded into a detent.
  2. As you turn the knob within the skirt, the tabs move forward from the edge of the skirt; at each detent, the tabs are set further forward. You can quickly visualize how knob drag is introduced: When the tabs are further forward, they press harder against the cellophane disk on the panel (which serves to provide a friction "bearing" for the felt tabs). They introduce more or less drag, depending on the number of detents you use.
  3. There are supposed to be felt pieces mounted on each of the two copper tabs. In my case, the felt was missing, and there was no sign they were ever present. They may have been removed by a previous owner or they may have been left off from the start. Had I attempted to introduce drag to my turning knob (p. 2-3 of Omni VI Plus instruction manual, section 2-5), the copper tabs would have scratched and damaged the cellophane disk and the plastic panel.
  4. To replace worn felt, or place felt on the copper tabs if they are absent, buy a 46 felt piece sheet. The item is entitled "Surface Guard" - 46 pieces, light duty felt blanket. Or find felt strips with self-adhesive. Pick two smallest pieces, and cut them into a square approximating the square copper tabs. Remove the backing, and allow the self-adhesive to hold each piece onto each copper tab. Or find some thin felt and try Duco cement (Ace hardware).
  5. In my case, when I turned the tuning shaft by hand, I noticed binding was still present over 90 degrees of rotation, even though the knob was removed. If so, you have some work ahead of you. You must remove the encoder, but first remove the thin cellophane circular disk from the panel, by gently using a small, thin screwdriver to get hold of one edge. Working slowly and carefully, pull the cellophane forward until you can grasp a section with thumb and forefinger. Now, very slowly, pull the entire cellophane disk off and put it into a zip lock bag with a label. You want to avoid tearing the cellophane disk. There is plenty of adhesive left on the panel for reapplication later.
  6. You're going to have to remove the encoder now. Work on a blanket placed on your workbench. To do so, remove the bottom and top rig panels by using a Phillips screwdriver on four black screws on each side. Once the panels are off, on each side near the front of the rig, there are two machine screws with washers that must be removed. Now, you can gently slide the front panel of the rig forward a little bit, allowing you to remove the tuning knob encoder. You have to remove a four prong wiring harness from the encoder first; it is easy to slide it backward. Locate a ½ inch Sears, Ace or SK Hex driver piece with a square or round hole in the center. Wrap several layers of electrical tape around the body of the hex driver. Tape a cloth over the front panel, use a pair of slender pliers to grip the hex piece from the side and loosen the nut that holds the encoder to the front panel. Take care to avoid scratching the front panel. The encoder can now be worked free through the bottom of the rig. My encoder in the Omni VI Plus was an Oak Grigsby 90Q125-02-00245.
  7. Hold the encoder in your hand and turn the shaft. Do you still feel slight binding during some of the rotation? In my case, the binding was still present, even after applying a little Deoxit D5 with a paper clip (part number D5S-6, Caig Laboratories, Poway CA 92064, www.caig.com). I use a thick paper clip, dip 1/2 inch into Deoxit sprayed in a small plastic cup, and apply. This prevents over application. This is a risk free lubricant for electronics and it has thin viscosity. My diagnosis, which turned out to be correct, was that the C clip plus the thin washer were too wide in the grove of the shaft, causing the encoder shaft to bind. This was an issue that came with the rig from the manufacturer. You could replace the encoder, but they are $45, and you might get another one with the same problem.
  8. Use two small, thin screwdrivers, on each end of the C clip, while pressing the encoder against a blanket on your work-bench, and push down on the C clip toward the blanket from both sides. Remove a very tiny washer and the C clip. Test the shaft rotation; in my case, there was now no binding.
  9. Get a piece of 400 sandpaper or emery paper, and using your forefinger, on a flat surface, thin down the C clip during two minutes of rigorous, circular rubbing. I worked on both sides, one of which is slightly rounded. Clean the C clip of any debris.
  10. Replace the thin washer first, and then the C clip on to the encoder shaft. If there is still binding, you will have to thin a little more, but be careful not to thin too much. Otherwise, you will introduce too much knob play.
  11. Test the encoder shaft. It should now rotate smoothly without binding at any point in the rotation. If it seems OK, add a bit of Deoxit lubricant/cleaner to the shaft as described above.
  12. Reverse the disassembly process of the encoder, front panel, top and bottom panels.
  13. Carefully, replace the cellophane disk on the front panel, taking care to center it.
  14. Now, make sure the copper tabs are at their furthest detent position inside the skirt. The idea here is to set the knob at the position that will have the least drag.
  15. Slide the knob onto the shaft as far in as possible, but do not force. Now, pull the knob back out about 1/16 of an inch, and trial-tighten the Allen set screw. You should have a free spinning knob.
  16. Adjusting the drag is not easy. Try using a pair of rubber gloves on one hand (my left) pressing the silver skirt against the front panel with thumb and forefinger while clicking the knob through a couple of detents. Clockwise tightens drag; counter-clockwise decreases drag. Finally, tighten the Allen set screw some more once you are satisfied that you have no drag, or some drag, depending on your preference. You may have to experiment a bit with knob placement on the shaft. You will notice a dramatic improvement in the smooth, silky feel of the tuning knob, especially for those who want a free spinning knob with no drag (I'm one of them). There will be some play when you grip the knob and move it side to side; this is normal. You can center the silver skirt if it is a bit off center; it is spring-loaded into position.
  17. Slide the rubber band and the exterior rubber "grip" strip back on to the tuning knob.
  18. In electronic restoration work, I've found Black Magic Pro Shine Protectant (available at Auto stores) an excellent product for cleaning and UV protection of rubber, plastic radio panels, knobs, and painted radio panels. It doesn't damage paint. My rig is in a brightly sun-lit room at 9,000 feet above sea level. Use a fine brush to apply a thin coat, let dry, and polish with a second fine brush or cotton cloth.

Peter Hoon VE1CHS

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