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Author Topic: MFJ ROLLER INDUCTORS ! ! FIX  (Read 15887 times)

Posts: 19

« on: January 02, 2007, 12:50:55 PM »

After reading all the depressing experiences with MFJ Junk, I just have to shine some light on this topic to bring everyone back-up out of the bottom of the hole.

I bought a MFJ-986 Roller inductor tuner that's always been trouble for me too. After a half dozen EMAILS to MFJ, and some idiot named Roger Stoob in technical service giving me garbage for answers I knew what I had to do.

I researched out buying a new roller inductor, that's B.S. - You're just gonna have (2) pieces of Junk. I thought about replaceing the Roller inductor with something off Ebay, those things were all the wrong size, or corroded so bad they were ready for the Junk Pile. I concluded- Fix what you got.

The main problem for poor contact on the little wheel and the inside of the coil is Angle of attack and Oxidation. here's the Fix I did I on my MIGHTY FINE JUNK Roller Tuner.

(First off)- I removed the Complete inductor set it on the Desk and Studied it. I seen the poor engineering and design on it. The Wire on the Coil Moved as the roller went round and round inside. That's no good. Pulled out the 5 Minute Epoxy and carefully (Using a Flat-Toothpick) mixed up some and applied Epoxy to all 4 sides of the coil
windings where the cheap Fiber supports the wire.

(Second)- Tighten up the loose screws they forgot to tighten at the factory. Inspect any Loose things with a super visual. Satisfied, the inductor now Felt SOLID, Nothing moved when you spun the coil. Re-Installed it.

Stuying it again- The Rod the moves the little pulley left and right was Straight on mine, With
the Roller Inductor facing you broadside, snap either end of the Brass support loose with an allen wrench.
Doesn't hafta to be loosened up entirely, just break it. Move that rod up on the right side
or down on the left side, whichever support end you loosened. Doesn't make any difference, that rod has to be tipped about 1/16" so the Angle-of-attack of the pulley isn't compromised. My Pulley kept Jumping off the track, and going in between the windings!

Lift the lever off that piece of Junk, "Harmonic Antenuator-Actuator assembly," unless you
really don't know what you are doing with antennas and really need this thing, disable it, all it will do is knock the pulley of the track again. It's crapola, el junko..

Now for those that are having arcing, contact problems. Metal-to-Metal Brass roller to Aluminum. Whatever, Even Silver, the best Roller Inductors it doesn't make a Hill-Of-Beans, they all oxidize. What I did was get a can of CAIG DEOXIT D5 Spray, Haven't found anything like it on the market, Radio Shack carrys it, its called POWER-BOOSTER. It comes in 2 little spray cans.

It has a chemical base to it that cleans the Inductor beautifully, Stuff a little Bounty paper towel (INSIDE) the roller with the end cranked all the way down. Spray a little of this on the paper-towel piece, Crank it up and down a few times, it'll turn BLACK as coal. Excellent!

Then with a needle-nose or tweezers etc,pull it out do it again. Twice should do it, 3 times for good luck! The BLACK with cease, and all you see is clear DEOXIT cleaner. You're done. After the cleaner de-oxidizes the Coil it also coats it with a electrical high conductivity coating to prefent further oxidation. You should be in good shape for about a year!

I been using mine now, and pumping 500 Watts thru it and it hasn't missed a beat. No intermittents, no problems, no MFJ.

We made a better product. Some prevent maintenance depending on usage, should go a long ways. I did service work in electronics for 35 years, now retired. 73 guys..

Posts: 1855

« Reply #1 on: January 03, 2007, 01:18:04 PM »

Good job.  Not many hams today can fix ANYTHING!  When I needed a couple of roller inductors for a tuner project a couple of years ago, I couldn't find anything second-hand in good condition and didn't like the looks of the MFJs.  While looking for variable capacitors, I learned that Cardwell, an old American name in variable caps, not only was still making capacitors, but also make roller inductors.  They're top quality just as the ones that were made decades ago.  There were two sizes available, depending upon the power rating you need.  I found the smaller inductors suitable for 1500 watts with no problems.

Posts: 8915


« Reply #2 on: January 04, 2007, 11:34:17 PM »

I used to drool over roller inductor tuners and think disparaging thoughts about my inductor switch until I motorized my MFJ switched-inductor tuner and thought about how long it would take to run a roller through the whole travel range.  These days, if I had a roller tuner that went south, I'd probably replace the inductor with a hand wound switched one, but good job on rehabbing yours!!

I gotta say I do still drool a little over YOUR roller tuner, K8AC ;-)



Monkey/silicon cyborg, beeping at rocks since 1995.

Posts: 121

« Reply #3 on: March 08, 2009, 06:31:37 AM »

Anyone have a line on a drive belt for the counter?  Mine came without one and I would like to replace it, so the counter will work.  Since it was not there I'm not sure what it looked like, maybe a rubber band type of belt?  Any info is appreciated, source of a replacement or otherwise. If you can help,please post here or e-mail. thanks. scott.

Posts: 1

« Reply #4 on: November 24, 2012, 06:16:00 AM »

I have two (2) MFJ roller inductor based tuners and cleaned both rollers and roller shafts with both rubbing alcohol and spray contact clearner with paper towels sitting under the roller inductor assembly.  This totally solved the "scratchy" rx and intermittent high SWR issues.  If I were to use any type of lubricant on the roller-to-shaft it would be the high priced stuff which contains lithium grease infused with silver (~60%) which has an extremely low electrical resistance even at RF.  IT IS EXPENSIVE so won't be getting any unless I need to revisit the issue soon.

Posts: 272

« Reply #5 on: December 07, 2012, 01:49:19 PM »

swduncan57 look for a place that repairs (if they are still around) tape decks and record player.  You will need to either take the tuner with you or make some measurements to determine the length.  Some years back and may still have it, I had a catalog for drive belts to record palyers and tape desks.

David S

Posts: 5688

« Reply #6 on: December 07, 2012, 03:31:53 PM »

A drive belt can be found at MCM electronics and they do have an online catalog. 

BUT - don't expect them to list it as being for the exact MFJ product. 

They instruct as to how to measure for the correct diameter and circumference, and you must know whether or not you need a round, square or flat belt. 

The counter inside MFJ tuners likely would work very well with a round or square belt. 

As for the posted, "FIX" -- others have noted that simply cleaning the roller inductor periodically is the correct REPAIR for the things.  Assumptions about bad designs and knocking the company or the designers and builders of products should be minimized, but it is what it is. 

My first wife had the cat FIXED. 

And he was always real different after that...

I left because I think she was thinkin' bout gettin' me fixed next. 


Posts: 6994

« Reply #7 on: December 07, 2012, 09:00:04 PM »

Have you tried to find an "O" Ring at your local hardware store and try it as a drive belt?  I've done this several times and they work great..... if you can find one of the correct length and thickness.  Just a FYI.

A Pessimist is Never Disappointed!

Posts: 2280

« Reply #8 on: December 14, 2012, 06:50:29 AM »

Yeah I have a 989c and have needed to service and clean the roller inductor twice in 6 years.

I wonder if anyone has ever adjusted the inboard power meter for accuracy?

Switch to dummy load then adjust the pot?

I am too lazy to take the cover off lately been busy.

Posts: 666

« Reply #9 on: December 16, 2012, 04:23:55 AM »

Hi everybody

I have bad experiences with the MFJ tuners in the past.
The worst experiences however popped-up when someone tries to tune antennas with a tuner when they do not know exactly how to tune a antenna.

These tuners are not that bad at all when they are used by hams that know how to use a antenna tuner and whom tune with care.
It also helps if you know what these tuners can tune and can not tune and why.

I have seen all kinds of blown MFJ tuner parts the past 10 yrs and more then 75% of those damages wouldn't be happening when hams knew a bit better what they were doing at that moment.

For myself I made the choice of collecting the best parts for a tuner that I could find and afford, and build my own tuner.
It is even based on a schedule from MFJ (the MFJ 9982), but just left out all parts that were not absolutely needed for tuning my antennas.
I left out all switches in the tuner for switching antennas etc.
Bought a very good and bulky and well build and designed Russian surplus variable inductor, and build 2 big strong high voltage and high current plate capacitors.
To be sure that these caps were as good as possible I welded the rotor plates and stator plates to have minimum losses.
I designed the inductor counter myself and it uses rather large gears , but it gives me very exact where my inductor is set.

It took me about 6 month to complete the tuner
This tuner is now finished, and i m very pleased with it.
The most beautiful part is of course that I van now say.
I build my tuner , that is much more satisfying then saying I bought my tuner.

So for those whom are considering to build their own tuner, try to find as much knowledge about tuners and the differences between different tuner designs, collect the parts you need and build your own tuner.

If you are not that handy still try to find as much knowledge as you can about antenna tuners and how they work and what the differences are between tuner designs, and what these differences mean for your situation and antennas.
Then buy the tuner that will satisfy your needs as best as possible.
It even might turn out that a MFJ tuner will be the right product for your needs, but at least now you know how to use it and what to do and what not to do with it.

good luck  Jos

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