Yaesu / Kenpro rotor repair
Yaesu / Kenpro Rotor repair tips received

Here's a collection of tips received regarding repairing the Yaesu / Kenpro rotors:
(No particular order, except links first)


Rotor repair reprint compiled by Bill, VE3NXK (Forwarded by WB6RWU):

Clive's, G3CMV, web page - go to the general satellite page.


The part numbers from my (W7KKE) invoice are:

S8000208 Bearing Ring(x2) price 3.40 ea 6.80 total
S8000209 Ball Bearing price 5.10 (package contains 40 bearings - all you need)

I didn't order it, but there is probably a gasket of some sort. I found remnants of one when I pried the housing halves apart. Ued some RTV gasket goop when putting the housing together.

Vertex Standard phone number: 714-827-7600 (ask for parts) When I mentioned bearings and retainer for a G-5500 the guy knew immediately what I wanted. Guess they get a frequent calls for these things.

The "Bearing Ring (x2)" are the retainers. They form a seal (sort of) as they press fit into the shaft hole.


Excerpts from emails:

From Don, KD4APP:

A couple of possibilities right off the top of my head from experience with my azimuth rotator:

1) Swap the cables at the rotators if you can - see if this helps - this verifies your cables and connectors. If you can't swap at the rotator end - swap at the control box.

2) Possibly the black wire going to the middle wiper of the feedback pot is loose - the first problem I had.

3) Possibly grease on the wiper of the feedback pot - on the AZ rotator it is an open unit - seems like a poor design to me.

From Allen, WB6RWU:

I spent time on the web searching for replacement screws and ball bearings. finally bought replacements from Yaesu, because I thought the stainless ones were too pricey for me. I went to Radio Shack and looked for some water proof gel, which had a moderately low viscosity. I didn't trust the product I found in R/S, but I did go to the manufacturer and find some. I called the company and spoke with them about my need and desire. They came up with a product and I bought some. I filled the pot with it.

I did coat some of the inner surfaces of the rotor, like gears and ball bearings, with a waterproof marine grease.

From Don, KD4APP (Forwarded by WB6RWU):

Have you tried swapping the cables (AZ<->EL) at the rotators to verify wiring?

It could also be a motor start Capacitor which I'm told is in the control box on the G5400 (in rotator on G5500 units) - swapping cables will verify the wiring and isolate where the problem is.

From Gerry, VE4QTB (Forwarded by WB6RWU):

Upon dismantling the rotor, we found that the set screw in the plastic gear was loose. Thus allowing the shaft to turn freely without turning the gear Consequently I had no elevation control of my antennas.

From Rick, W2JAZ (Forwarded by WB6RWU):

1) If the EL meter in the control box is still working move it to 90 deg.

2) You will probably need to buy an impact driver at an auto part store as I did. Mine cost $20. This is almost required to get the philips screws out and separate the shell

3) Put match marks on the two clam shell halfs before removing

4) also migh want to take not, or mark, the orientation of the boom tube before taking it all apart.

Mine is still apart since my problem was that the EL rotor was not reporting back through the parallel interface to the control software. I'm in the process of replacing and end stop switch (which I broke) and the internal rotor pot which seemed to be the source of the problem. I will of course clean and regrease everything before reassembling. You'll also need to buy some liquid gasket type material when you put the clam shell case back together.

From F.Costa, CT1EAT (Forwarded by WB6RWU):

I hope I'm not late to gave you a tip. It's a real pain to remove the 8 screws of the box. But I've found the worst part is to remember how to put everything back inside, in the right position. I guessed, and as soon as I turn it on, it went on the wrong direction and broke one of the micro switch. I had to open it again, replace the damaged part, and assamble it, again. This time I look first to the photos I shoot while I opened it. So, if don't trust your memory, shoot every detail while you open it. It while be precious later.

From Dave Smith, W6TE (Forwarded by Kevin Smith, N3HKQ):

I have found someone that will service the Yaesu Az/El rotors at a fair price. He completely disassembled my G-5400B Az/El, cleaned and re-lubricated all the gears and re-assembled both rotors. He also cleaned the 500 ohm pots that were intermittent. He did a great job and I can highly recommend him. His name is Larry Kramer, K6VLF, and his phone number is 559 264-0772 (Fresno, CA). He is available for servicing Yaesu rotors at $50 each plus parts and shipping.

I have no connection with Mr. Kramer other than a very satisfied customer. If you have a rotor in need of servicing, you might give him a try.

From Jim, wb4gcs@amsat.org (via AMSAT-BB)

I've had a full- blown, full auto az-el setup, in VA -- which is milder than where I am now (PA), but still, saw ice and snow.
I never had weather issues.

I did have design issues: The Yaesu G5400 is GROSSLY underdesigned. My first indication of this was when the elevation motor seized, taking out the power transformer, FOLLOWED by the fuse. Later, I had ANOTHER elevation motor failure, despite ENSURING that there was no unbalanced torque. This time damage was limited to the motor.


1. Make SURE that your entire array is balanced such that the elevation rotor is not trying to lift a bunch of weight, merely overcoming inertia (which is plenty if you have a 2m cross yagi).

2. Replace the fuse that comes with your rotor with the lowest value slow-blow which will not fail under starting load. This is how I prevented further cascading failures.

3. If you run any kind of automatic control (recommended) make SURE that it has decent stall detection/protection. If it issues a move command and doesn't see motion in some number of seconds, it should turn off all motors, inform you, and do nothing else until manually reset. Not all products meet this test, I'm told. Full disclosure: My software was homebrew, and I'd implemented what I thought was rigorous stall detection, but obviously not. Turns out that there were some subtlties with using multiple interrupts in DOS that I didn't initially understand, so insufficient testing did not disclose that my software was not doing all that I wanted. After the first failure, I did some more rigorous testing and sorted it all out.

4. If you run automatic control under MS Windows, be careful. I'm told that if Windows has an error (Critical stop??) which presents you a message you need to respond to (like an attempt to write to an empty floppy drive) EVERYTHING, including background tasks stops until you hit "OK". (I've NOT tested this, and behavior may be improved with newer, more preemptive versions of the OS, but I'd verify before trusting.) External devices, like Steve Bible's Easy Track may get commands from Windows tracking S/W, but do not care what windows does if they detect a stall -- they respond appropriately. For this reason, I now prefer Easy Track to my homebrew hardware/software, except under DOS (which works just fine to track and work 9K6 baud birds.)

Design notes: The G5400 has no thermal protection for the elevation rotor, only limit switches at the extremes of elevation -- which are absolutely useless if a tree grows into the arc of your 2m longboom antenna.. The Azimuth motor DOES have a thermal trip inside it, tho it's held to the motor windings with a cheap piece of tape, which dries out and separates, leaving the sensor hanging in the air -- which I discovered when I had to repair the position sensor pot because the cheap tape failed, allowing the fine wire to the slider to break due to fatigue failure. I repaired with good tape backed up by a UV ty-wrap. This is why, despite trees, I never had to replace the Az motor.

I'm TOLD (no first-hand experience) that the G5500 has no thermal overloads, only limit switches. It appears to be a bit more rugged mechanically, so there's hope if you implement the recommendations above regarding stall protection and fusing.

Again, I had NO problems, despite Ice storms and snow. The above passed on for lessons learned/knowledge sharing.


From Stan, WA1ECF (via AMSAT-BB)

For the Yaesu model G-5400B az/el rotator system.

For the elevation head potentiometer: between terminal 1 and 3 is the complete winding of the pot, 500 ohms, fixed.

The wiper is at terminal #2.

What ever the elevation position is, the sum of the resistance between terminals 1 and 2 added to 2 and 3 is 500 ohms on or about.

If measuring at the control box, the wire resistance is only a few ohms, so we are still talking about 500 ohms.

The motor windings are terminal 4-5 is both windings in series, about 7 ohms as measured at the control box. Terminal 4 to 6 and 5 to 6 are the same, about 3.5 ohms as measured at the control box. These readings includes the cable resistance.

Keep in mind there is a motor winding thermostat that will trip out when the winding heats up due to being locked up. It will reclose automatically after cooling down.

From Fred, ZL1BYP:

(Second email)

The grease I used was a silicone lubricant called Molykote 111 from Dow Corning. I picked it up - a 100gm tube - at a local engineering outlet. It's designed as a fluid valve and O Ring lubricant and it's appeal to me was that it was resistant to 'washout'. That was the important thing in my book as the bearings themselves are - to say the least - pretty crude as ball races go. There is no specialised bearing grease - to my knowledge - designed for the bearing surfaces involved in these units. Molykote 111 was reasonably slippery - and it would stay there - what more does one need in that situation?!

I can't comment in detail on how well it's done as I haven't had cause to take either of the two rotor sets down for examination or repair. They just run on. Perhaps that says it all.............!!!

First email from Fred:

For what it's worth. I stripped my Kempro rotor sets about 6 years ago and found that the balls had corroded leaving a large ridge on one particular ball. This had 'picked up' a spider finger and it was in the process of using the spider unit as a scraper which was scraping away the groove in the aluminium casing. It was the grunching of this that alerted me to the trouble. With the rotor above the shack window I heard the change in noise immediately and stopped it straight away! ( As a marine engineer of some 40 years standing any slight change of sound 'in the ship' is noticed immediately and looked into.................!!!!)

I ditched both of the (very crude) spiders in the rotor and made up the difference in (stainless) steel balls leaving about a "one ball" (5/16") gap so they could roll easily in the track. It's been running very nicely ever since.

I picked up a retirement job at a local university at about the same time and it involved some experimental work using PoSAT on its commercial frequency bands. I did the same thing to the rotor set there before I put it up and that set tracked every pass (using KCTetc.) 24/365 for 4 years (!!) - less a 48hr shutdown when a disc drive failed in the PC - and that's still running beautifully now locked - for the hell of it - on AO-51. (Keep 'em active is the way to keep 'em servicable in my book).

Stainless socket head cap screws is also 'spot on' as replacements for the (dreadful) cross slot case securing screws.

Use plenty of antiseize compound on the threads and - yes - keep the drain hole clear in the bottom of the casing; most important.

From Domenico, I8CVS:

The eight head screws are originally lodged by the nanufacturer using loctite.

An impact driver can damage the threads and the screw can break inside.

To remove the screw with easy is enough to heat the head using the flame of a general purpose gas torch while gently unscrewing.

From John, KC8ZFN (including exchange with Stan, WA1ECF) :

Thanks for the tips. From Ken's pictures it does appear that moisture is getting in form the top of the el rotor where the two casing halves meet. I like your lapping for better fit idea.

I think Permatex "form-a-gasket" would not introduce much spread between the halves, but I'm glad you made that point.

I like the idea of tapping grease nipples at the bearings. Anti seize is in order too as you say.

I've yet to get my hands on the G5500 bought in unused condition from a list member, but before it goes up it will be disassembled and treated to some Boeshield T-9 on the inside of the casing and perhaps an enlarged drain hole with a screen cover to keep critters out. I'll follow your suggestions too. That pic of Kens is scary!!

(Stan's email which prompted above reply regarding John's comment "...separate the housings and apply some Permatex gasket sealant."

UGH.... Wrong direction to take

The case halves are precision machined to allow a proper mating of the ball bearing surfaces. adding a gasket will open up the bearings to allow a sloppier fit and greater opportunity to leak inside.

Adding gasket cement to the case halves would make it very difficult to open up later for service.

If anything, I would inspect and if needed, lightly lap the case half mating surfaces to allow a better (tighter) fit around the circumference and grease the case halve mating surfaces with a tenacious grease.

Keep in mind that the drain hole in the bottom of the case is there for a purpose, and may need to be periodically cleared of insects.

Fabricating a cover over the el rotator would do more to keep the rain and dust out of the bearings.

In time, the steel ball bearings and race rust away. The bearings become elongated and do not roll. As the bearings become loose, the gear train unmeshes so the pot is not connected for a el indication or is intermittent. The corroded, rusty, gritty abrasive, bearings start chewing up the softer alloy case halves at the bearing.

An interim solution would be to replace the steel bearings with stainless steel ones and eliminate the bent sheet metal race (bearing separator), adding more bearings to compensate, as needed.

The long term solution is a seal on each bearing surface to keep the acid rain out and to add a grease nipple at each bearing to allow periodic maintenance.

On a new unit, all hardware should be removed, one at a time and a antiseize compound used on the threads to allow maintenance later. Avoid excessive compound in blind holes that may hydrostatically lock the screw. See the folks at the auto parts store.

If you use the separation kit, treat those threads also. The separation kit rusts up in a hurry so use a tenacious lubricating grease on the threads "that will be used". You will see the advantage 5 years from now. I use a 1 lb tub of boat trailer bearing grease from Wal-Mart, will last 5+ years. Use an acid brush to apply.

Use a dielectric silicone grease on the connector pins and backshell before you seal it up with coax seal and tape. This grease is available from auto part stores.

From Nicolaus Sallay, PP8DA

I strongly recomend not to use lithium grease, because this mixes with water and looses its greasing ablity. I recomend a grease with molibdenium dissulfite, comecialy known as Molicote or similar brand name. It has excelent lubricating quality's and is long lasting and even in lot temperature conditions it still works. It seems to me that the dark, black colored grease originally used in the rotors are of the above tipe.

Beware of clogging the botom drain hole of the rotor.

From Larry, KE4PM

It wouldn't hurt to use stainless allen head cap screws. Much easier to open with a allen wrench. Honda used to use phillips head screws on their bikes. They switched to allen head screws and it made it much easier to dissassemble.

From Gopal, VU2GMN

I have had to open up my rotor a couple of times and the first thing I did was to replace all the screws with Allen Head screws. Yaesu use those INSIDE but not on the OUTSIDE where they should have. That way the next time you will have no problem.

It is also a painful exercise to align the cross boom tube so that it matches with the pot reading. After several efforts, what I did was to run the motor with the tube out and get the reading on the dial to the halfway mark. Then drop in the tube so that the mechanical stop is opposite the motor. One has to make sure that the very thin beryllium copper or similar plate used to activate the end stop micro switches don't get bent as then the motor will drive past the stop and chew up the mount. This has happened to me once, with the micro switches also being broken by the mechanical stop. It has been suggested to me that next time I mount a couple of micro switches external to the rotor on the boom with a actuator so that one can adjust them accurately. I will do that the next time I have to open the rotor.

I also suggest that the whole operation is done inside a plastic basin to catch the eventual dropping of ball bearings etc.

From Bill, W5PGZ

While you are in those drives, it would be worth your time to weather proof those az-el pots. Here is how I did it. Get some prescription bottle caps that will fit over the back of the pots. Now, with clear nail polish, carefully look for any seam or joint line on the body of the pot and seal it. Litely sand the back of the pots and then wash them with alcohol. Wash the inside of the bottle cap with alcohol. Apply a coat of a good adhesive to the back of the pot and snap on the cap. I snapped the cap on over the wire from the pot center, making sure there was sufficient turning play wire inside the cap. Seal the cap/pot surface with wx sealant.

I live in southeast TX where the humidity is very high along with high salt content in the air. My G5500 was up < 1 year when BOTH pots went south. They are expensive to replace($30.00 each) and are quite fragile.
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