Yaesu G-5500 Elevation Rotator Repair

In a previous post I described how my G-5500 rotator had failed and would no longer elevate my antennas. Based on what I was seeing at the time and a quick check with a DVM I believed that one of the motor windings had failed and had gone open-circuit. The failed rotator unit sat in the garage until recently when a friend mentioned that his G-5500 had the shown same fault and he “fixed” it (albeit temporarily) by giving it a sharp tap with a rubber mallet! Evidently the limit switches can stick “open” and this would give the same indications that I had seen.

Having read several online posts describing the repair of various rotator units I decided that I would have a go at repairing my unit. Based on what I’d read it would seem that I was quite fortunate as the eight M6 fasteners used to hold the two halves of the rotator housing together unscrewed fairly easily. What I found when the housing was split open was also pretty consistent with what others had posted.

 

You can can see from the photos above that there was a lot of solidified grease, rust and other debris in the bottom of the housing. The balls were badly corroded and the ball retaining rings had both broken up. The missing “fingers” making up some of the horrible debris.

Having got this far I decided to recheck the motor windings and was surprised, and very pleased to find them now both okay (measured 3.7 ohms per winding). I checked both limit switches, pressing them many times and could not get either of them to “stick-open”! As the motor was okay I decided to investigate sourcing the two ball retaining clips and a set of 40 balls.

An online search resulted in only one source that listed the ball retaining rings and they were based in Holland. An email inquiry to Yaesu UK resulted in a quote for all the parts that I needed. Fortunately everything was in stock and a few days later I had some new shiny parts.

The housing cleaned up fairly easily and fortunately the four bearing surfaces were not damaged. I feared that the pieces that had broken off the ball retaining rings may have got trapped between the balls and gouged the surfaces.

The motor was removed and the gearbox taken apart. I took a number of photos to ensure that I would put things back together correctly. In addition to the photos I carefully marked the position of the various rotating parts. All the various cogs in the gearbox were undamaged and simply needed a good clean.

Once all the parts were cleaned I checked all the cogs were in good condition and gave them a thin coating of the long life grease. The 20 balls and new retaining ring were fitted to each half of the housing. I used a thick, dark, Moly type grease to to lubricate all the metal on metal moving parts. Things went back together without any major issues, the photos taken before were certainly useful when it came to reassembling the gearbox.

 

I decided not use any liquid gasket when I fitted the two halves of the housing together as I wanted to test the rotator first to ensure that everything worked.

As things turned out that was a good decision as I found that after moving up and down a few degrees the rotator seized when trying to rotate upwards a second time. This had me scratching my head as I was certain that I had reassembled everything correctly and I knew the gearbox rotated freely. I could hear that the motor was trying to spin but it couldn’t. I removed the motor to test if that would spin freely on its own and discovered that it was the motor assembly that was at fault.

The motor has a white plastic assembly which houses a circular spring and bow tie shaped fitting that’s attached to the motor shaft. This forms a braking system to stop the motor continuing to spin when power is removed and thereby minimising any overrun. On close inspection I discovered that the grub-screw that secured the bow tie fitting to the shaft was loose allowing it to move along the shaft and catch on the wrong side of the spring. This then stopped the motor from spinning in one direction!

Needless to say this was the only part of the rotator that I did not check as part of the rebuild. Once the bow tie fitting was set in the correct position on the shaft and the grub-screw tightened the motor ran perfectly in both directions.

 

Once everything was reassembled the rotator was retested and worked as expected.

 

Lessons Learnt

  • Taking time to photograph each stage of the teardown can prove invaluable when it comes to reassembly.
  • IMHO the rotator housing needs either an additional drainage hole or the existing one enlarging to help drainage.
  • The positioning of the bow tie fitting is critical and should it slip and cause the motor to jam there is the risk of damaging the motor winding.
  • I’m still unclear what caused the rotator to stop and not elevate. Initial investigation with a DVM suggested one half of the motor winding was open circuit. However this could also have been due to the limit switch being stuck “open”. After taking everything apart I found that both limit switches operated correctly and the motor windings were fine. I did find pieces of the ball retaining clips stuck between the balls and housing. The fault occurred when the rotator reached zero degrees and I went to elevate up. I suspect now that the limit switch did “open” and the finger debris caused the lock-up. Maybe in hindsight I should have replaced the limit switches. I guess time will tell.
  • As I only need a maximum elevation of 90 degrees (not the full 180 degrees that the rotator can do) I plan to mount the antennas so they are horizontal when the rotator is mechanically at 10 degrees. My tracking controller can manage this 10 degree offset easily. By doing this the safety limit switches should never operate unless something goes wrong.
  • Some form of plastic hood over the rotator housing and boom clamps should help reduce water ingress and extend the operational life of the unit.

 

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