Wobbly Heath SB-series LMO repair --------------------------------- >From: "Gary H. Harmon, Jr." Nick, I just went through the same problem with a SB-100. My "wobble" was solved by spraying some cleaner on the tuning gears inside the LMO. I had to remove the LMO to get to the screws on one side. I guess the gear meshing mechanism gets dirty and introduces the wobble. Anyway, it fixed my problem. Good luck. GARY ======================================================================== >From: Chuck Penson My 102 exhibits the same wobble, but only until it warms up (20 mins or so). It is not a big problem--yet, anyway. I have always assumed the problem was that the grease on the bearings is getting thin and/or stiff. I have heard some people complain about some kind of "slip ring" contact inside the LMO, and that it can get dirty and result in that kind of symptom. Maybe some others in the group can shed some light on that. ===================================================================== >From: MIKE SANDERS > Nick, I had 2 SB110s that had the vfo wobbles. They were exactly the same. I had talked to a couple other fellas who had same situation with other LMOs in the Heath stuff. Never heard of a cure but a fix is to run the tuning end to end many times until wobble disappeared. Yeah, I know its not what most are looking for but it works. The unit will function fine until it is left to set again for a time. My 110s worked great all summer during the Eskip season on 6 but each year I have to rerun the LMOs to get them stabilized at the beginning of the season since they had sat for months with very little attention. The SB104 spinner knobs sure help to "crank" em. Bottom to top maybe as many as a dozen times. I assume an oxidation barrier is being broken but never could prove it with mechanical attempts at repair or cleaning. Good Luck 73 de KS0F ============================================================================ >From: "Greg Anders" My SB401 and 301 have experienced the same symptoms and I`ve received the following tips for troubleshooting. 1. The rotor ground clip can be intermittent and should be cleaned to insure a constant ground. 2. The reduction drive and/or capacitor bearing may be stiff and need cleaning and relubrication. 3. The drive gear may be worn (good luck finding a replacement). In addition, on my SB301 I found that the drive pulley which rides on the steel track on the dial was bent slightly making the pulley gap inconsistent on one side. I removed the pulley, disassembled it and carefully attempted to "re-bend" the pulley with needle nosed pliars to make the gap more consistent throughout its circumference.... I`m sure there are others on the list who have experienced this problem with Heath LMOs so you will probably get a lot of help. ============================================================================ >From: sick@admin.swcc.cc.ia.us (Wade Sick) I once owned a Heath SB-100. It had the problem in the LMO that you described. The reason for the problem, which was explained to me by another, more experienced SB-100 user, was that the tiny bearing in the drive of the planetary-type tuner mechanism get dry and move in a jumpy (quantum leap) fashion, rather than in a nice, smooth fashion as the more expensive rigs would. Even my later model SB-104 has a mechanical problem similar to that in the VFO. I never got ambitious enough to tear out the LMO. I tried different times with the SB-100 to squirt WD-40 in the general direction of the gears, but I don't think it ever did any good. There is an LMO in the SB-110 that I own too, but for now it seems to behave okay. That problem was very frustrating back then, especially for finding CW stations. Even though I do miss it, selling it to trade up to a Kenwood TS-520 was the easiest solution to the problem. ================================================================= >From: "James C. Owen, III" Since there seems to be a large? number who have the wobble problems with the Heath SB series rigs and since I sucessfully fixed mine a number of years ago I will edit and post the suggestions I gave in private E-mail to Dave KK5HA. I owned as SB-100 for better than 15 years and it was my main rig most of that time and I also had the wobble problem. I think that the only difference in the SB-102 LMO is that it was made solid state. The problem with mine was that the end bearings in the LMO capacitor got worn. When torque was applied to the shaft the shaft first moved sideways before it started turning. The fix was very easy but took some time. The LMO has to be removed from the rig and the case taken apart, not hard but again it takes some time. I took the tuning capacitor completely out but that may not be required. BTW this did not effect the tuning of the LMO very much. If you look at the back end of the capacitor you will see that there is an adjustment for endplay. Just back off the locknut and turn the adjustment slightly to put a little more force on the rotor shaft and then reset the locknut. This may be all that is required. If you like check the slip-ring type of connection that grounds the rotor to be sure its making good contact. Of course check the pinch drive on the dial to be sure its not slipping but I never had any trouble with this. I must say that from what I'm told the LMO from the SB-100 and early SB-101's was better than the LMO that was used in the SB-102. If you find that you can't fix yours than maybe you could find a junk SB100/101 and use the tube type LMO. This wouldn't be hard to do but you would need an SB100/101 schematic to see where the B+ was picked up. This was a great rig and just kept on working. Hope you get it fixed and if I can answer any other questions just ask. =================================================================== >From: Kim Herron What your friend is experiencing is the typical wobble or variation in capacitance that is experienced when a tuning cap is turned and the ground strap on the rotor is dirty or corroded. I have fixed several of those and they are not hard to do, just time consuming and a bunch of screws to take out. If he removes the LMO from the receiver [transceiver] and then removes the front cover [thats the one with all the red painted screws that no-one is supposed to fool with], then he can get in there and clean the contact portion of tthe rotor strap. Put a very light coat of lubriplate on it and put back together. He will probably have to reset the linearity adjustments, but it will cure the warble. Linearity can be adjhusted through the front access holes that are silver taped shut. I do it with a freq counter. ================================================================ >From: wlfuqu00@service1.uky.edu (Bill Fuqua) I have had the same problem and got a second SB-301 (cheap) that was to be used for parts. However both had backlash in their LMO's. The problem is that the anti-backlash gear has one brass part and one phenolic part. The phenolic wears out. Most other Heathkit products had all brass gears. The solution is not easy. I have done this twice and will never do it again. You must remove the LMO and carefully remove the Capacitor and gear. This required that you remove the printed circuit board. Be very careful. One problem is that the dial shaft goes thru a hole and you must either disassemble the box, which is very difficult or do as I did and use some metal shears and cut between the edge of the box and the hole so that you can bend the small bit out and away so the shaft will clear the box. Fully close the cap and mark the shaft and gear. Loosen the grear and rotate it 180 degrees. so that you will be using the unused part of the gear. Tighten the screws and reinstall it into the box. Now for the hard part. You thought you were done, right! These are not precision gears. You will find that the dial will be off by a few KHz now may be up to 5 KHz. You can either live with it or correct it. I did this with the LMO out of the receiver so that I could get to all the adjustment holes. Now remove the foil tape over the adjustment holes. and attach to a screw a piece of stiff wire on top to bend over the dial to make a pointer. Use the adjustable capacitor and the coil to set the end points of the LMO range on the dial. A frequency counter is very usefull here. Remember the lmo frequency goes down as you tune higher in frequency. Start at the higest frequency on the counter or Zero on the dial and tune up 10 or 15 KHz on the dial. Use a small plastic tool to carefully bend the segmented capacitor plate over that is over lapping the stator. As you tune up on the dial is best to allow each new segment to overlap the stator and compare the frequency with the counter ( some calculation required) and then make your adjustment. The next thing to do is to cover the adjustment holes. I used foil covered duct tape from a hardware store. This is very thin material with a paper backing that you pull off to expose the adhesive. This will take many hours and you may have to make a second pass. I managed to get both LMO's within about 250 Hz across the band. This is not a project for an in experienced operator. ==================================================================== >From: "James C. Owen, III" >From experience with a SB-100 with the same problem. It's wear in the bearings of the VFO capacitor, at least it was in mine. Remove the cover of the VFO release the locknut on the adjustable bearing turn the adjustment a quarter of turn or so, check for play and tighten the locknut and try it. If you have severe problems you may have to completely disassemble the VFO capacitor and worm drive and clean and lub it good. Don't worry it's not as hard as it sounds and calibration will not suffer. =====================================================================